keylab 49 power problem

[junshi]

Hello.
Please take advantage of the help of everyone with a wealth of experience and knowledge.

I am repairing the Arturia KeyLab (1st generation), a MIDI keyboard I inherited a few years ago.
I was able to fix some keyboard floats and fader lever dropouts, but the main thing is that the power won't turn on.

The power supply is specified to be supplied from 5v500mA from the PC's USB or DC jack, but there seems to be a problem in both cases, the display does not appear and the PC does not recognize the keyLab.

I am an amateur, but I think that there is a problem with the power supply because the LED on the main board does not light up. We were able to confirm two things: 5V is flowing through the USB connection part of the board with a tester, and 5V is flowing through the board when the DC adapter is connected to the DC jac.

The three electrolytic capacitors have no visible bulge.

I would appreciate it if you could point out what to check and what to doubt.
The keyboard and faders have been repaired, so I'd like to get it working somehow.
I posted the front and back images of the main board.

thank you.

[MajorFubar]

What you really need is a service manual or schematic. These days, companies don't share things like that with the public like they used to. Go back 30+ years and it really was not unusual to find a printed schematic either in the back of a product's Owners' Manual or on a folded piece of paper inside the product when you remove the cover. But the world has changed and products are not designed to be repaired anymore, they're designed to be efficiently recycled after you buy something new.

You do seem to have correctly nailed the issue to being power-related. A multimeter will allow you to trace the 5V from the input jack through to the power switch and beyond. Maybe a component has failed and is open-circuit, or maybe the problem is caused by some other basic electrical malady such as a bad solder joint or a crack/split in an electrical trace. Fix the problem, and likely everything will suddenly spring into life. Good luck.

[junshi]

Thank you. It's a pity that I can't get the circuit diagram, but I will carefully trace the board with a tester.