This desk came to me completely dead no power lights or anything. These desks are pretty simple beasts and there really isn’t much in them to go wrong. With the symptoms I assumed that this was probably a case of a bad connection as they do seem to suffer from the multi-pin leads becoming corroded. On opening the desk I noticed straight away that the power supply output capacitors had bulges in the top.
This isn’t uncommon in electrical gear of this age as these components have a finite life. I checked the rails going to the channel strips for shorts but all measured well.
I removed the power supply PCB and found this.
Im not sure if this is factory bodge work or not but all the connections seem to follow the traces so maybe it was done for mechanical reasons.
After removing the capacitors and replacing with new ones with a slightly higher voltage rating had to do a bit of filing (always a good idea if you can make them fit)
The power supply was still dead. Not surprising really but now I went after the voltage regulators seen above the capacitors these are two lm317 variable voltage regulators and a lm7915 negative voltage regulator. These are used to produce the +15 -15 and 48 volt phantom power.
One of the lm317 reg’s was still happily working away but due to it being of similar age I removed and replaced all three for good measure. At this point all voltages were restored and I got the top of the console plugged in for a test.
The mixer was back from the dead. Left it playing songs for a few hours and kept a eye on its temperature around it heat sinc but all is now well.