75 Replies Latest reply on Jun 14, 2021 8:38 AM by jw0752

    Dimmer repair

    wal_e

      Hello everyone,

      First of all I would like to apologize, I might certainly be in the wrong section, but I have been sent here by the Farnell technical assistance and to be honnest this place is a real maze for me

      So, I have been trying to fix a dimmer that went working only as a simple switch : OFF to ON max light directly. Following my researches it seems that the origin of my problem is a faulty triac and also - maybe - a capacitor ; I have tested both of the 2 fuses and they are ok.

      The two original component are labeled:

      - BTB04-600A

      - CBB62B X2 0.033µF (250-280VAC) dimensions 40/110/56/C

      My problem is that I can't find any of the exact two components and I have no idea what I can use to replace them as equivalent.

      Any help is really appreciated

      Thank you - very much - in advance.

       

      W

        • Re: Dimmer repair
          shabaz

          Hi,

           

          If rotating the dimmer makes it turn the light on and off, then why do you think the triac is faulty? Couldn't it be the rotary potentiometer? (I don't know - I'm speculating).

          I'm not sure it is good to replace with alternatives if the original parts are unavailable in your region, and there's assembly risks too (e.g. replacing it may require replacing insulating washers).

          Anyway, I think you need to consider that it could be something else faulty. By the time you replace the triac and/or capacitor, and then discover you now need to order something else, all that plus your time will cost >> than a new dimmer, and may be >> unsafe.

            • Re: Dimmer repair
              wal_e

              Hello Shabaz,

              Thank you for taking the time to answer. I found this diagnostic on the internet, it says that if the dimmer only works from OFF to ON max power it's a triac issue.

              As you can imagine this is not a vital issue but I like fixing things instead of just replacing them I can't help it .

            • Re: Dimmer repair
              jw0752

              Hi Walid,

               

              If you only have off and on and when the dimmer is in the on position it is always at full brightness then the most likely problem is the Triac. You can test this with a continuity tester when the dimmer is removed from power by checking the continuity between A1 and A2 terminals. It should be open under normal circumstances. If it is shorted then the triac is bad. The other components are probably OK. The BTB 04-600A is a 4 Amp 600 Volt triac and can be replaced with pretty much any triac that has ratings of more than 4 amps and 600 volts. I have some BTB 06-600 which would be 6 amps and 600 volts. If you are inside the USA I will send one to you. If you are looking at the triac with the pins down and the label facing you the A1 and A2 terminal are the left pin and the center pin. The right pin is the gate and should be attached to a DB3 trigger diode if you have a standard design.

               

              John

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                • Re: Dimmer repair
                  wal_e

                  Hi John,

                  Thank you for your help I really appreciate your kind answer but I am too far from you that would make this triac very expensive So, I am experiencing exactly what you described and already replaced the old triac with a new one labeled BTB08-600BW (the only "equivalent" triac I found in the neiborhood) which didn'ty solve the problem. So I just tested both of them and both of their A1 and A2 show no continuity....does that mean they're both open and ok ? When I tested the capacitor I got a 0.0µF instead of 0.033µF...is it possible that my tester is not sensitive enough or is my capacitor is dead ? In that case could he be the origin of the problem ?

                  Best regards,

                   

                  W

                  1 of 1 people found this helpful
                    • Re: Dimmer repair
                      jw0752

                      Hi Walid,

                       

                      I looked a little closer at the standard dimmer circuit and the capacitor is also quite important. My schematic shows a 0.33 uF but that is probably for 115 VAC and you are probably working with 230 VAC. If your meter can check capacitors the 0.033 should not be too small for it to read. It should indicate 33 nF. I was wrong before about testing the Diac. It should not show any resistance in either polarity on your ohmmeter. Diacs do not break down and trigger until they are in the area of 30 V plus.

                       

                      John

                      2 of 2 people found this helpful
                        • Re: Dimmer repair
                          wal_e

                          Hi John,

                          My meter is digital and unfortunatly not a fancy one...I tested both triacs, BTB04-600A shows 1.9 mega ohm between A1 and A2 and goes to 0.6 kilo ohm when A2 and Gate shorted. BTB08-600BW shows 13.3 mega ohm and then 80 ohm when A2 and gate shorted.

                          I tested again the original box capacitor and it shows 0µF instead of 0.033 µF (or OL?). I have a spare polypropylene capacitor marked 333K (and 400VMY) which should be 0.033 µF but when tested it shows 677 µF :/

                          I found another spare polypropylene capacitor marked 103K (and 630 FN) and showing 0.1 µF when tested, maybe this one could replace the original one ?

                          What do you think ?

                          Thank you in advance.

                          W

                            • Re: Dimmer repair
                              Jan Cumps

                              wal_e  wrote:

                               

                              Hi John,

                              My meter is digital and unfortunatly not a fancy one...I tested both triacs, BTB04-600A shows 1.9 mega ohm between A1 and A2 and goes to 0.6 kilo ohm when A2 and Gate shorted. BTB08-600BW shows 13.3 mega ohm and then 80 ohm when A2 and gate shorted.

                               

                               

                              The TRIAC measurements are OK

                               

                               

                              I tested again the original box capacitor and it shows 0µF instead of 0.033 µF (or OL?). I have a spare polypropylene capacitor marked 333K (and 400VMY) which should be 0.033 µF but when tested it shows 677 µF :/

                              I found another spare polypropylene capacitor marked 103K (and 630 FN) and showing 0.1 µF when tested, maybe this one could replace the original one ?

                              What do you think ?

                              Thank you in advance.

                              W

                               

                              OL is usually range overload. That means that te capacity is higher than the DMM can show in the active range.

                              33 nF is typically supported by a DMM. Does your meter have an option to change range for capacity measurements?

                              333K is 33 nF, So that is a good one.

                               

                               

                              I found another spare polypropylene capacitor marked 103K (and 630 FN) and showing 0.1 µF when tested, maybe this one could replace the original one ?

                              That's also an off measurement. 103K should be 0.01 µF / 10 nF.

                              I would not put a 10 nF where the 33 nF is expected ...

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                                • Re: Dimmer repair
                                  wal_e

                                  Hi Jan,

                                  So I can solder back the original triac on the pcb ?

                                  My DMM has auto range selection I can't change anything, in the manual, for capacitance it says :

                                  Measuring range 600 µF -> résolution 0.1 µF

                                  Measuring range 6000 µF -> résolution 1 µF

                                  In both cases: accuracy : +- 4% reading + +3digits

                                    • Re: Dimmer repair
                                      wal_e

                                      So I tried putting back the original triac and replacing the capacitor with the 333K and it didn't work...same problem: from OFF to ON max power but no dimming function...

                                        • Re: Dimmer repair
                                          jw0752

                                          Did you test the DIAC. Small cylindrical component with two leads that is between the gate of the Triac and the capacitor?

                                           

                                          John

                                          • Re: Dimmer repair
                                            jw0752

                                            The Trigger diode or DIAC is a critical part of the dimmer circuit. It is designed to show a very high resistance to AC current until the voltage exceeds its thresh hold at which time it conducts.

                                             

                                            https://en.wikipedia.org/wiki/DIAC

                                             

                                            In the dimmer circuit the control (probably 500K Ohms) in series with a current limiting resistor( probably 10K) and the capacitor form an RC timing circuit. The setting of the control causes the voltage on the capacitor to rise at different rates. As soon as the voltage on the capacitor exceeds the threshold of the DIAC it fires and turns on the Triac which remains on until the AC current in the circuit passes through the zero point. The period for 60 Hz line voltage is 1/60th of a second and in this time the current passes through Zero twice. The AC line current will automatically turn off the Triac every 1/120 th of a second. If the Diac is shorted there will be no delay since the threshold of the diac will be zero volts and the triac will be triggered very early each 1/2 cycle which will give the appearance of full brightness regardless of control setting. If the DIAC is working properly the triac will not be triggered until much later in the half cycle and it will give the appearance of being dimmer.

                                             

                                            John

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                                              • Re: Dimmer repair
                                                wal_e

                                                Hi John, thank you for these explanations I guess it is the last possible malfunctioning element ? How can I test the Diac knowing that my DMM can't do it ?

                                                Thank you in advance

                                                 

                                                W

                                                  • Re: Dimmer repair
                                                    jw0752

                                                    Actually your meter should be able to test to see if it is shorted. Put the meter on Ohms and test across the DIAC. A short or very low ohms would be bad. Breaking the connection of one of the leads to the circuit should also cause the Triac to stay turned off. If the light no longer turns on with the switch when one of the diac leads is disconnected this would further confirm that the Triac is OK.

                                                     

                                                    John

                                                • Re: Dimmer repair
                                                  jw0752

                                                  Here is the Newark listing for the DIAC DB3 which is the most commonly used DIAC in the dimmer controls.

                                                   

                                                  https://www.newark.com/stmicroelectronics/db3/diac-28v-to-36v-do-35/dp/89K1258

                                                   

                                                  John

                                                    • Re: Dimmer repair
                                                      wal_e

                                                      It is too narrow for me to try disconnecting one of the leads it is a bedlight dimmer and everything is compacted. My DMM shows OL when testing de Diac in Ohm mode. I asked a friend for his professional DMM. I will test the db3 c531 and let you know but will most certainly replace it anyways...

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                                                        • Re: Dimmer repair
                                                          jw0752

                                                          Never thought to ask: What type of bulb are you using in the lamp?

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                                                            • Re: Dimmer repair
                                                              wal_e

                                                              Good question indeed, I am using a regular incandescent bulb.

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                                                                • Re: Dimmer repair
                                                                  jw0752

                                                                  Hi Walid,

                                                                   

                                                                  In order to do some experimenting I built a dimmer circuit on bread board.

                                                                   

                                                                   

                                                                  The first thing I learned from doing this is that my explanation of the circuit a few posts ago was at best simplistic and probably incorrect. My Experiments indicate that your Diac is likely OK. The capacitor value is fairly critical. Too much capacitance and the light stays on high. Too little capacitance and the light stays on high. No capacitance and the light stays off. Shorted Diac or one with parallel resistance and the light stays off. No Diac in circuit and the light stays off. I am sorry as this may not simplify or help much. If you have experiments that you would like me to run let me know. I will leave the bread board assembled for a few days.

                                                                   

                                                                  John

                                                                  2 of 2 people found this helpful
                                                                    • Re: Dimmer repair
                                                                      wal_e

                                                                      Hi John,

                                                                      I am really glad to see that here are persons like you whom put all that effort to help others. So, I changed the Diac and nothing changed still from Off to On full brightness. This, with your last message about the importance of capacitance lead me to think that, in fine, it's the capacitor that's dead or faulty and unfortunatly I couldn't find the exact same one to replace it. I took some photos of the controller and the DMM I borrowed from a friend so if you have any suggestions or ideas please let me know, I would be happy to explore further more.

                                                                      Best regards,

                                                                       

                                                                      Walid

                                                                        • Re: Dimmer repair
                                                                          Jan Cumps

                                                                          If you put the DMM in the 200 nF range,it should give a good measurement of that cacitor. : The value 33 - or something within 10% of that.

                                                                          You need to fit the capacitor legs into the 2 slots with capacitor symbol.

                                                                          Discharge the capacitor first.

                                                                           

                                                                          It's indeed a good DMM.

                                                                          1 of 1 people found this helpful
                                                                            • Re: Dimmer repair
                                                                              jw0752

                                                                              I would like to know if the lamp lights with the DIAC out of the circuit.

                                                                               

                                                                              John

                                                                                • Re: Dimmer repair
                                                                                  wal_e

                                                                                  No John, the light stays off whithout the DIAC...

                                                                                    • Re: Dimmer repair
                                                                                      jw0752

                                                                                      Thanks for running the experiment which confirms that the Triac is OK and that the Diac is also OK.  Verify that the resistors have the proper values and then the only thing left is the capacitor.

                                                                                       

                                                                                      John

                                                                                        • Re: Dimmer repair
                                                                                          wal_e

                                                                                          So here are the mesured values:

                                                                                          C1 (yellow original one) labeled 0.033 µF reads 3.1 when DMM on 200 nF

                                                                                          C2 (small capacitor behind the big one) labeled 683K reads 70.1 when DMM on 200 nF

                                                                                           

                                                                                          R1 (red, red, orange, silver or grey) supposed to be 22 Kohm reads 0.02 when DMM on 2 Mohm

                                                                                          R2 (blue, grey, brown, gold) supposed to be 0.68 Kohm reads 0.665 when DMM on 2 Kohm

                                                                                          1 of 1 people found this helpful
                                                                                            • Re: Dimmer repair
                                                                                              Jan Cumps

                                                                                              C1 is not OK

                                                                                              C2, R1 and R2 measurements are OK

                                                                                                • Re: Dimmer repair
                                                                                                  wal_e

                                                                                                  Thank you for the feedback Jan, problem is from what I understood C2, R1 and R2 are part of the main syteme that works to dim the light...C1 and the coil are here to reduce the amount of parasites emitted by the Triac and thus are "optional"....still the system doesn't work...

                                                                                                    • Re: Dimmer repair
                                                                                                      jw0752

                                                                                                      What is minimum and maximum resistance of the control?

                                                                                                        • Re: Dimmer repair
                                                                                                          wal_e

                                                                                                          Can you please be more specific ?

                                                                                                            • Re: Dimmer repair
                                                                                                              jw0752

                                                                                                              The knob that you turn to select dim or bright is a variable resistor. It has two terminals that attach at the edge of the board.  When it is at dim I would expect a reading of several hundred K Ohms . When it is at the bright position I would expect a low Ohm reading.

                                                                                                              John

                                                                                                                • Re: Dimmer repair
                                                                                                                  wal_e

                                                                                                                  That knob is also used to go from OFF to min light, at that point (even when in off position) it reads 14.6 when DMM is in 20 Kohm and when max bright light it reads 1.8 when DMM is in 200 ohm.

                                                                                                                    • Re: Dimmer repair
                                                                                                                      jw0752

                                                                                                                      See if you can remove the solder from one leg of the control so that it is separated from the circuit trace. Try the dimmer with power on. The light should stay off. Unplug the unit and check the resistance of the control again with the one leg still detached. When you read the meter watch to see if a "K" is displayed with the number on the display. What are the minimum and maximum position resistances?

                                                                                                                       

                                                                                                                      John

                                                                                                                        • Re: Dimmer repair
                                                                                                                          wal_e

                                                                                                                          Hi John, I "drew" the circuit of the dimmer. Here the control is labeled P and has 3 legs: 2 that you can see on the other photos and one under it. Please let me know which one I should remove the solder from.

                                                                                                                            • Re: Dimmer repair
                                                                                                                              Jan Cumps

                                                                                                                              Walid, can you double-check the circuit around the potentiometer P and R1?

                                                                                                                              On your circuit that looks like a dead end. It only has one wire connected to the circuit.

                                                                                                                                • Re: Dimmer repair
                                                                                                                                  wal_e

                                                                                                                                  Hi Jan, sorry I indeed forgot some part of the circuit but it doesn't involve the paret you pointed. Here is a corrected drawing and the photo of the back circuit annotated.

                                                                                                                                    • Re: Dimmer repair
                                                                                                                                      wal_e

                                                                                                                                      My mistake, phase in is lower. Here is corrected:

                                                                                                                                        • Re: Dimmer repair
                                                                                                                                          jw0752

                                                                                                                                          Hi Walid,

                                                                                                                                          The two connections at the center of the board are the ON OFF switch . If you can remove the solder from either of the other connections at the edge of the board so that the metal leg from the P control no longer touches the copper you will be able to perform my experiment. Nice job on drawing the schematic. I am not sure that it is totally correct as the switch isn't where I would expect to see it in the circuit but who knows. This experiment is to verify that the control is working properly. Once the leg of P is no longer touching the circuit copper traces you will have to touch the meter to the two legs to get the resistance readings.

                                                                                                                                           

                                                                                                                                          John

                                                                                                                                            • Re: Dimmer repair
                                                                                                                                              wal_e

                                                                                                                                              Thank you John. Am I supposed to test it while light is at max light or dim ?

                                                                                                                                                • Re: Dimmer repair
                                                                                                                                                  jw0752

                                                                                                                                                  We need to get a resistance reading on the two legs closest to the edge of the board in the dim position and the bright position. Make certain there is no power to the system when these readings are made or you may damage the meter.

                                                                                                                                                    • Re: Dimmer repair
                                                                                                                                                      wal_e

                                                                                                                                                      The holes are too narrow the legs are still touching the pcb...I am going to take it away and test it away from the circuit is that still ok ?

                                                                                                                                                        • Re: Dimmer repair
                                                                                                                                                          jw0752

                                                                                                                                                          Sure that will work.

                                                                                                                                                          • Re: Dimmer repair
                                                                                                                                                            jw0752

                                                                                                                                                            I have to leave for a while. I will check back in a couple hours.

                                                                                                                                                            John

                                                                                                                                                              • Re: Dimmer repair
                                                                                                                                                                wal_e

                                                                                                                                                                Okay, here are the mesures:

                                                                                                                                                                Max light: 1.7 when DMM is on 200 ohm

                                                                                                                                                                Min light: 16.8 when DMM is on 20 Kohm

                                                                                                                                                                OFF: oscilating between 16.8 and 17.5 when DMM is on 20 Kohm

                                                                                                                                                                  • Re: Dimmer repair
                                                                                                                                                                    jw0752

                                                                                                                                                                    My first question is: Did this dimmer ever work to your knowledge?

                                                                                                                                                                     

                                                                                                                                                                    Your readings on the variable resistor are 20 times smaller than what I would expect them to be in this design. Is it possible that this unit is a manufacturing defect where they accidentally installed a 20K variable control when they intended to install a 400K?

                                                                                                                                                                     

                                                                                                                                                                    Do you happen to have a high ohm potentiometer like a 500 K that we could patch into the circuit to see if we can get it to dim. If you have such a potentiometer let me know and i will tell you how to patch it in to verify this theory. As i am sure you already know you have to be careful as we are dealing with hazardous and possibly fatal voltage levels in this circuit.

                                                                                                                                                                     

                                                                                                                                                                    By the way your excellent technical skills have made this troubleshooting adventure a lot of fun.

                                                                                                                                                                     

                                                                                                                                                                    John

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                                                                                                                                                                      • Re: Dimmer repair
                                                                                                                                                                        wal_e

                                                                                                                                                                        Thank you John I remember it working perfectly yes. When you asked about the 500K potentiometer, I remember seeing this on the one installed : B500K

                                                                                                                                                                        This can't only be a coincidence right ? So how this could be malfunctionning ?

                                                                                                                                                                          • Re: Dimmer repair
                                                                                                                                                                            Jan Cumps

                                                                                                                                                                            Great sleuthing, John. +- 17K for a 500K potentiometer is indeed off.

                                                                                                                                                                             

                                                                                                                                                                            Walid, the potentiometer upper housing and shaft are plastic for your safety - it's wired to your power outlet without isolation.

                                                                                                                                                                            I'd advise to use an equally well isolated one, if you are going to replace it.

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                                                                                                                                                                              • Re: Dimmer repair
                                                                                                                                                                                wal_e

                                                                                                                                                                                I started to look for an equivalent on the internet...most of the ones I saw have 3 front legs :/

                                                                                                                                                                                Just out of curiosity, isn't it possible to fix it ? Or at least to try to understand what happened to it?

                                                                                                                                                                                For your information, as a novice, I certainly tried an economic bulb at some point...

                                                                                                                                                                                  • Re: Dimmer repair
                                                                                                                                                                                    jw0752

                                                                                                                                                                                    It is very very unusual for a control to change value. I have seen situations where too much current has damaged and changed controls but usually the resistance goes up and not down. If the control had some sort of contaminate that was an electrolyte spilled on it the resistance might come down. If you can find a replacement, which may be a challenge, you could raise the metal tabs on the body and open the control up to see if anything internally is evident. By the way you can turn any of the three legged potentiometers into a two legged one by cutting off one lead.

                                                                                                                                                                                     

                                                                                                                                                                                    John

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                                                                                                                                                                                    • Re: Dimmer repair
                                                                                                                                                                                      jw0752

                                                                                                                                                                                      I just thought of another possibility. It is possible that the wiper inside the control has come loose from the shaft and has limited mobility near the low end. Bend the metal tabs up and open the control and check it out. You can also test the carbon strip by putting your meter from one end to the other. I bet we will see 500K or there abouts. If the wiper is loose perhaps you can fix the control by reattaching it.

                                                                                                                                                                                       

                                                                                                                                                                                      John

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                                                                                                                                                                                        • Re: Dimmer repair
                                                                                                                                                                                          wal_e

                                                                                                                                                                                          Here are the photos from inside the control:

                                                                                                                                                                                          Lower part, we can see the ON-OFF mechanism

                                                                                                                                                                                          Please let me know if you have any remarks regarding their looks. I noticed that the inside is quite "greasy".

                                                                                                                                                                                          Which part is the wiper ? the one attached to the plastic white rotating knob ?

                                                                                                                                                                                          • Re: Dimmer repair
                                                                                                                                                                                            wal_e

                                                                                                                                                                                            The mesure of the outer strip is 0.555 when DMM is on 2 Mohm.

                                                                                                                                                                                              • Re: Dimmer repair
                                                                                                                                                                                                Jan Cumps

                                                                                                                                                                                                wal_e  wrote:

                                                                                                                                                                                                 

                                                                                                                                                                                                The mesure of the outer strip is 0.555 when DMM is on 2 Mohm.

                                                                                                                                                                                                That is normal, for a 500K potentiometer ...

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                                                                                                                                                                                                  • Re: Dimmer repair
                                                                                                                                                                                                    wal_e

                                                                                                                                                                                                    That's what I thought too...so is there any way to fix it ? Should I clean the wipers with soft sand paper and rise them a bit ?

                                                                                                                                                                                                      • Re: Dimmer repair
                                                                                                                                                                                                        wal_e

                                                                                                                                                                                                        So I tried cleaning the strips with a soft clothe, sanded sofftly the wiper and rised them a bit too...reassembled the control and tested the resistance between the two legs : 0.553 when DMM is on 2 Mohm. Resoldered the control and tested the switch...worked a bit as a dimmer, heard a few "sizzlings" but still managed to dim a few times then went back to ON-OFF only...

                                                                                                                                                                                                          • Re: Dimmer repair
                                                                                                                                                                                                            jw0752

                                                                                                                                                                                                            Looks like you found the source of the problem at least and you can get a replacement control from EBay. Sorry for all the hoops you had to jump through but the failure of a control like this is very rare and not very high on my list of suspects.

                                                                                                                                                                                                             

                                                                                                                                                                                                            John

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                                                                                                                                                                                                            • Re: Dimmer repair
                                                                                                                                                                                                              Jan Cumps

                                                                                                                                                                                                              wal_e  wrote:

                                                                                                                                                                                                               

                                                                                                                                                                                                              So I tried cleaning the strips with a soft clothe, sanded sofftly the wiper and rised them a bit too...reassembled the control and tested the resistance between the two legs : 0.553 when DMM is on 2 Mohm. Resoldered the control and tested the switch...worked a bit as a dimmer, heard a few "sizzlings" but still managed to dim a few times then went back to ON-OFF only...

                                                                                                                                                                                                              The sizzlings are not normal. The capacitor (C1 in the schema you posted) normally drops the majority of the voltage before it reaches the potentiometer.

                                                                                                                                                                                                              My guess is that if you do not replace the capacitor, and buy a new potentiometer, you will have a repeat of the issue after replacing the potentiometer..

                                                                                                                                                                                                                • Re: Dimmer repair
                                                                                                                                                                                                                  wal_e

                                                                                                                                                                                                                  Hi Jan,

                                                                                                                                                                                                                  I found an equivalent control but that's why I was initialy here: no way to find the C1 capacitor on the internet: CBB62B X2 0.033µF (250-280VAC) 40/110/56/C.

                                                                                                                                                                                                                   

                                                                                                                                                                                                                    • Re: Dimmer repair
                                                                                                                                                                                                                      wal_e

                                                                                                                                                                                                                      By the way, does anyone recognize the logo/name on this capacitor ? Would be helpful. Thanks in advance

                                                                                                                                                                                                                        • Re: Dimmer repair
                                                                                                                                                                                                                          jw0752

                                                                                                                                                                                                                          I am in disagreement with Jan on the need to replace the 0.033 uF cap. My experience tells me it is OK and that the failure was in the control due to contamination or lubricant failure that has cause an arc path to form between the wiper contact ring and the resistive material. I am however just a technician and Jan is one of the top Engineers on the Forum so one has to respect his opinion. Depending on how difficult it is to find the proper capacitor you will have to weigh whether to use the original or replace it. On the link I gave you it is difficult to judge the dimensions of the component. You may want to check the Data Sheet to make sure it will fit before you order. The move from a 250V cap to a 630V cap will not affect operation but it may make the new one a larger size.

                                                                                                                                                                                                                           

                                                                                                                                                                                                                          John

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                                                                                                                                                                                                                            • Re: Dimmer repair
                                                                                                                                                                                                                              wal_e

                                                                                                                                                                                                                              Hi John, sorry for the late reply I was away from home. In the datasheet I found the reference of the exact capacitor I need to replace thank you. You said something that caught my attention : "lubricant failure". Is the lubricant here to optimize the contact between the wipers and the stripes? Because when cleaning the control I wiped it clean and didn't replace any before reassembling. What kind of lubricant can I use ? Thank you

                                                                                                                                                                                                                                • Re: Dimmer repair
                                                                                                                                                                                                                                  jw0752

                                                                                                                                                                                                                                  I don't really know but I speculate that the grease is there as an insulator, a conductor of heat, an arc suppressor, and probably for the cosmetic feel it imparts to turning the control. If you are able to open the control again without breaking the metal retention tabs you should inspect the insulator between the metal slide ring and the black resistive strip near the bright end of the turn as that seems to be where the short is.

                                                                                                                                                                                                                                   

                                                                                                                                                                                                                                  John

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                                                                                                                                                      • Re: Dimmer repair
                                                                                                                                                        jw0752

                                                                                                                                                        Tonight I hooked up the oscilloscope as I wanted to see the change in the signal on the gate of the triac as the potentiometer was turned from a dim setting to a bright one. Channel one (Yellow) shows the source AC voltage and syncs the horizontal trace. Channel two (blue) is the gate of the triac and the trace on the Hantek Scope is across the bulb. Note the RMS voltage as we go from very dim to full brightness.

                                                                                                                                                         

                                                                                                                                                         

                                                                                                                                                        Dim Setting

                                                                                                                                                         

                                                                                                                                                         

                                                                                                                                                        Bright Setting

                                                                                                                                                         

                                                                                                                                                        Note of Caution. Taking readings of AC line voltage can be dangerous. I used an isolated bench AC source for this experiment and a portable secondary scope so than I would not have an Earth or Common ground conflict.

                                                                                                                                                         

                                                                                                                                                        John

                                                                                                                                                        1 of 1 people found this helpful
                                                                                                                                  • Re: Dimmer repair
                                                                                                                                    jw0752

                                                                                                                                    Hi Walid,

                                                                                                                                    It sounds like you got a good substitute for the triac. If you have an analog dial type multimeter you can test the triacs with the meter. Put the range on Rx1 and put the leads on A1 and A2 of the triac. Now use a small screwdriver to short the gate to the center A2 pin. A good triac will go to low resistance and stay there until you remove the meter leads or short A1 and A2 together. To continue your trouble shooting test switch the polarity of the meter leads on A1 and A2. Connecting the gate to the center lead should again cause the triac to go low resistance just like before. Triacs are designed for AC so the conduct in both directions. Next step is to test the diac which is a small two lead device attached to the gate of the triac. It should not be shorted though it may conduct in one polarity. As long as the capacitor is not shorted it is probably ok.

                                                                                                                                    John

                                                                                                                                    3 of 3 people found this helpful
                                                                                                                                      • Re: Dimmer repair
                                                                                                                                        colporteur

                                                                                                                                         

                                                                                                                                        I extracted this rotary dimmer circuit schematic from a video. I added the letter references. A=Load and B=neutral.

                                                                                                                                         

                                                                                                                                        If I read your explanation correct E & B sides of the triac will read low resistance when the gate F is triggered. Reverse the leads across the triac and it should provide a low resistance reading also.

                                                                                                                                          • Re: Dimmer repair
                                                                                                                                            jw0752

                                                                                                                                            Hi Sean,

                                                                                                                                            This test works best with an analog meter that uses at least two batteries (3V) in it's Ohmmeter function. Range Rx1 is also best as this delivers the highest current to the device under test. This is because the triacs need a minimum current to keep the triac A1 A2 junction saturated once it is triggered. The triac should be tested with both polarities on A1 and A2. Once the Triac is triggered you can reset it by shorting A1 to A2 or by removing one of the test leads. 90 percent of the time this test can be performed in circuit as long as the board is powered down.

                                                                                                                                            John