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I have an old radio ITT Schaub-Lorenz Touring International 103 which had small issue with bass control circuit. Issue was caused by "cold joint" around the potentiometer used for bass regulation.

 

Here are steps of the radio disassembly:

1. Remove the knobs from top panel.

Knobs remove.

2. Unscrew all screws from rear panel.

Rear panel.

Rear panel.

Rear panel.

Rear panel.

Rear panel.

Rear panel.

3. Unscrew all screws from top panel.

Top panel.

Rear panel.

4. Remove rear panel.

5. Unscrew two screws located near the handle.

Front panel.

6. Remove front panel. Be careful because speakers are connected with wires to main board.

Front panel.

 

Debugging part.

schematic

After short analysis of part of schematic related to tone control circuit and quick measurements of continuity I have found that issue was caused by "cold joint". There was no connection between of R334 potentiometer and C388 capacitor. The "cold joint" was marked by red square on one of following pictures.

debug

debug

debug

After re-soldering of this joint, the issue was fixed. Here is short video of disassembled radio.

 

Here is short video after issue fix.

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This fix is from a few years back.

 

One day, a train arrived outside

One day my wife turned up with a large bag of train track and asked me to pop out to the car to get the rest. I also found a small ride on train in the boot of the car. "I picked it up from the charity shop, it's not working" she said "but I'm sure you can fix it".

I looked the train and soon discovered it had a 6v Lead Acid Battery under the seat. I used a multimeter and determined that it was quite flat.

 

Battery Charger

I did not have a charger so did some googling and discovered that it was possible to make one. I found an L200 regulator kit in the bottom of a drawer and added a high wattage "sense" resistor to limit the current. I also added a couple of bits of old PC heatsink, one to the regulator and one to the resistor and boxed it all up.  This allowed me to charge the battery.

Tear down

Once I had a charged battery I tried powering it up but nothing happened, so I needed to take it apart. To get to the electronics I pretty much had to strip it right down. I started from the bottom where I found some screws and followed the wires and screws till I had exposed all of the circuitry. I was quite an involved process so I made notes as I went. These were written up as an iFixIt guide.

Working through from the battery I used a multimeter to see where the power was getting to. My first stop was the main power switch which is togged by a lever on the top of the train. This is a dual throw switch but only one pole is used. The connected side was not working so I checked the other. I was luck in that this was working. So I swapped them over and reversed the switch by 180°, I could now get power to the motors and some lights and sound but the train only went backwards.

 

Next up was the lever on console that controlled the direction of the motors. This was a simple mechanical problem the lever had been moved too far and was no longer activating the switch. A simple repositioning resolved that problem.

Also one of the sound switches was not working. At the time I had no suitable replacements so I gave it a clean with some contact cleaner. It was tempremental but sometimes worked to generate a sound effect.

 

My last fix was cosmetic but I think makes a good improvement. The bumpers were paper stickers and had deteriated. I used some metal from some old computer parts and plastic from a shreader to make some new ones. These were turned on the lathe and glued in place with some builders adhesive.

 

 

Train and Tracks

 

Train Returns

Over the next couple of years the train was used on sunny days but we noticed that both the train was struggling to drive along and my daughter was stuggling to fit on it. So we bundled it all up and returned it to the charity shop where we'd first bought it from. Hopefully at least one other family will get the same enjoyment from it as we did.

rsc

Potentiometer Repair

Posted by rsc Oct 24, 2017

Simple Electronic Repairs

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I published this on Instructables.com a while ago, but it's a good one.

How to Clean the Controls on Your Amplifier: 10 Steps (with Pictures)

 

Is that crackling and popping when you turn the controls on your amp driving you crazy? 

Here's how to clean them and get back to the music.

There are spray "contact cleaners" available for this purpose, but in most cases just mixes the dirt and grime already inside with more dirt and assembly grease and may make the control operate worse than it is already.

Step 1: Remove Mounting Knobs and Nuts

The first step is to remove the knobs and nuts mounting the controls to the front panel to the amplifier. 

Remember to keep all the parts sorted so you can find them later.

Step 2: Unsolder the Controls

After the circuit board is removed from the amplifier box, each control is removed and cleaned one part at a time. 

Do not take them all off at the same time, because you may mix them up.

Step 3: Remove Old Solder

Remove old solder and inspect the pads for any burnt or broken traces.

Step 4: Open the Control

Open the control (potentiometer or "pot") by lifting the mounting tabs slightly. 

Remember that these tabs will not handle being bent more than a few times before they break off. 

If a tab breaks off, you may be able to solder it back on later.

Step 5: Inspect Dirty Contacts

The control is made up of two main parts.  The contacts and the carbon resistor. 

Each side must be cleaned without damaging them further. 

If the carbon looks burnt or has broken areas, the entire control may need to be replaced. 

If the contacts are worn too much or broken, the entire control may need to be replaced.

Step 6: Cleaning

Carefully, clean the contacts and carbon with a pencil eraser. 

Do not push too hard, and clean the eraser on a piece of paper when it gets too dirty. 

Do not use any cleaner or solvent except rubbing alcohol or cleaner designated for this type of control. 

Make sure to blow off any eraser particles left on the control before assembling the part.

Step 7: Cleaning Continued

If you are cleaning a dual control, the method will be the same, however it will take twice as long,

and you must align both controls so they go back together correctly.

Step 8: After Cleaning - Reassemble the Control

Being careful not to forget any parts, recrimp the case making sure not to bend the case or trap any parts between the case and the parts inside. 

Turn the control and check for a nice smooth motion from the 0 to 10 locations.  The control should move approx. 120 degrees without any binding or bumps.

 

If you think you assembled one incorrectly, set it aside, and open the next one to look at how it should be assembled to fix the last one. 

If you need to, take pictures of each phase to help you reassemble the parts later.

 

Try not to get any grease or oil on the contacts while assembling the part.  There may be some grease on other areas of the control, but it is not intended to be on the contacts. 

There is a special conductive grease that can be used on the contacts, but is not necessary for proper operation.

Step 9: Resolder and Continue Cleaning the Rest of the Controls

Use new solder to assemble the clean control back onto the PCB. 

Clean the solder flux off with some rubbing alcohol or flux remover.

 

Step 10: Finish and Test

Put the PCB back into the cabinet, and test the amplifier.  Turn each control and make sure it works as it should.

That's all folks, enjoy your "good-as-new" amp.

It took me about 2 hour to clean this Peavy, so at a tech rate of $60 per hour, I saved a bunch of cash doing it myself.

 

I had many comments from DIY "experts" telling me they just spray this or that or air or WD40 and all is well, but in my experience you

must take them apart to truly get the corrosion and oxidation off the carbon and the contact points.  I'll quote myself:

Once again I say, there's no magic spray that will turn grease, scratches and dirt into pure gold and silver. Spraying a bad solder joint will not make it conductive again, spraying a cracked PCB trace will not fix it.

If you read through the comments, you'll see how frustrated I was with some of the responses.

 

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(Please click here for the Audio version of this document)  <------If you don't feel like reading click to the left.

 

 

So I have had this booster pack sitting around my shop I use it all the time and even use the air compressor on it quite often too.  I have a feeling they are not meant for such abuse and it finally gave out so after almost a year of it not working I thought it would be a great opportunity to start my adventure into repairing it.

 

I had a ton of ideas that I was wanting to do with this project but felt I would try to find something practical and something maybe nobody else would do.   Since video game systems and anything relating to them has been done before by me over the years I wanted to step away from that and other things that I usually repair because that would be simple.  way to simple and would feel like I was cheating.

 

This brought me to the Booster pack with compressor on it since it was electronic and also mechanical it would be fairly straight forward....this was what I thought.

 

I decided to open up the compressor part only six small screws but the wires leading into the main compartment where short so I had to open up the rest to see if I could get a bit more play from the cables to the compressor unit another  10-14 screws there.

Finding the slack I needed I began to investigate the pump, it's a nice setup. It was built better then I thought it would be.

 

 

The pump was fairly dirty so I decided I would clean up all the parts re-grease the piston and housing to see if it work on further investigation tho I noticed the ring around the piston was worn and damaged and it set inside the top of the piston ring so I had to come up with a solution.

 

At first I decided I would use a o-ring at the top of the tube seemed like there would have been enough clearance.   Well there wasn't I overloaded the pump and blew the fuse since there was not enough clearance as I hoped there would have been. And this is where the fuse came into play.

 

But first back to the piston on the pump how did I resolve this?  Well I took a o-ring a smaller one, that I could stretch  around the piston and then take my Dremel my very not so good battery one.  I slowly sanded around the O-Ring until it would fit in the tube with just enough pressure.

Then I took some white grease and grease it up good this time anything below the ring got a lot of grease.  Hopefully this will help I thought to myself as I know it does get fairly hot even tho its just a small piston.  After getting it all back together after I oiled all moving parts with a drop of all purpose oil just to make sure its all good and works out any dirt that might be in any parts.   I went to turn it on.

 

Zero, Zilch, Nada, nothing was happening since I blew the fuse.

 

 

So now it was time to open up the main compartment to see how much fun it was going to be to replace the fuse.  I have had other booster packs where they actually have the fuse (blade fuse) located on the outside of the unit.  But this one had one on the inside and was pretty much going to have to be replaced with a proper fuse holder just in case it blows again. (bulb style fuse holder)  Sure I could just copy the way they have it but to me I was thinking more of the long term if it blows again for any reason I would be able to quickly remove the side and swap the fuse.

 

Instead of  undoing the battery, pulling the battery, re routing wires, cutting zap straps, pulling boards and loosing springs (still need to find that).    As you can tell I am sounding like I am still working on it while I am writing this well that is because I am I thought I would document this far and finish up with the fuse replacement and see how things went.

 

 

Now I was happy I blew the fuse it actually gave me a great opportunity to play with my bench top Micronta multi-meter.  (my baby) Which I finally got cables for. They seem to be a odd sized plugs.

 

So it seems there wasn't a spring as stated before which I was missing. When I flipped the one cover over to see if I could get a better view on the housing to view the fuse holder connection to the main board , the buttons fell out.

 

Even when I went to desolder I ended up desoldering the led light on it thinking it was the right one.  But made a mistake and had to go one over which is fine.  Finally got everything soldered up and the new fuse holder in no thanks to my soldering iron that seems like now after many years has decided it was time to break on me good thing for backup parts.   So will have to get that done at a later time as I really enjoy my soldering station.

 

 

So now I needed a 15amp fuse for the holder. I have tons of fuses do you think I had one?...nope.  So 10amp fuse it is for testing the compressor I will have to order some 15amp ones and get that replaced.   So after getting it all back up and together I was looking inside the case to see how much room I had in areas. I think there might be a spot I can put  a fuse holder on the outside.  But for now undoing 10-14 screws is ok with me now that It has the fuse holder in it instead of just the fuse with leads on it.   Kind of silly how many people would just toss this out if it blew a fuse.

 

 

Below is my video on me taking it apart and testing, was a great time and was actually glad I blew a fuse (not on purpose).   Now to see if I can find more of those compressor pumps.