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.
This O2R turned up with dead channels and a few weird problems. Ignoring the few weird problems for now I took it apart looking for the obvious. (by the way these are a pain to get to the boards for the encoders)
You can now see the ADC board responsible for converting the analog signals into digital. This board uses AK-5390VP that is also equivalent to the CS5390 ADC chips.
On inspection of the boards I found this.
The desk as obviously taken a knock at some point and the PCB has cracked. After removing the board the track side also had obvious damage and a quick test with the multimeter confirmed no continuity for a few of the tracks. This kinda explained why most of the effected channels were on one side of the desk.
This isn’t a very good picture I know but if you look closely you can see that the tracks carrying the digital signals from the ADC chips as the tail end of the crack going through them.
With some very tedious soldering and gluing of wires I eventually restored continuity to all the broken tracks.
I also bridge the ground plane to restore ground to the far side of the PCB. If this was necessary Ive no Idea.
Well after all this I was hoping that the channels would all just come back life but as it is with these this its never that easy is it.
Stereo pairs 21 and 22 and pair 23 and 24 still did not work. Due to each pair sharing a ADC I decided that maybe the these had gone bad and pulled out the oscilloscope and the AK-5390VP datasheet . The signal going into the chips was fine but the outputs were completely dead. I removed these chips and fitted sockets waiting for replacements to come. The desk is now useable but missing the mentioned channels why I try and obtain these chips from a reliable source.
A bit of a update but I have also now confirmed these chips dead as I borrowed one from a working channel to check so sadly I may have to resort to china for parts. Parts for china can be a bit sketchy as they like to make a lot of fake chips that are no longer in production. Most of the time just removing the number off a similar part and selling it as something else.