I do not have an answer for you. Perhaps you could post a few pictures of the board and wiring. I thought I would acknowledge your question so that it would go back to the top of the cheque.
The “wiring” is very simple. The 2400mA power supply was plugged into the desktop board. USB devices plugged in were a keyboard, mouse, camera and an external hard drive. In addition, a display was connected to the HDMI port and a speaker to the A/V port (who also derived power via a USB connection). No SSD drive installed.
I verified that power was getting to the power connector on the desktop board. The volt bus was 0 volts (verified by checking voltage at the Raspberry Pi connector to the desktop board). The fuse on the incoming power is OK, and the incoming power is present on the switching regulator. But there is no voltage on the inductor.
Plugging in the power to the Raspberry Pi board itself works. There is 5V at the connector. I did this without any peripherals plugged in and with the keyboard, mouse and display plugged in to the Raspberry Pi itself. 5 volts was getting to the desktop board as well.
It appears that the switching regulator is not working. I may have overloaded it with all the peripherals plugged into the USB ports. I need a schematic/parts list to figure out what failed and to replace parts. I am quite familiar with switching regulators – I design them into our controller products for the HVAC industry.
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The fact that no one has come forward with a schematic leads me to believe that the schematic isn't available. Do you have a recourse to return the board as defective? I can't believe that they would have designed a board with peripherals and then not designed the power supply to support those peripherals. If you can't return the board and if you are able to identify the switch chip you should try replacing it or at least look up the data sheet and see what reading should be expected on the individual pins.
I have had the Pi desktop for a couple months. Tonight, I tried to power it up but I have no LED.
Disassembled the boards from the box.
Plugged power into Pi itself and it powers up.
Plugged power into the desktop board and no power to Pi.
Checked voltages around U2 which appears to be a switching regulator. 5.27 volts to pin 4, but L1 has no voltage, which indicates to me the FET in the chip is not switching.
Does anyone have a schematic, or suggestions for repair?