Further testing on the main board (right ). I think I’ve located the problem, one of the 4580 in the Mix-B path is at 14.80v on all it’s pins… Gonna swap that with a new one and see if it changes anything.
Got my mixing desk back from a long term loan and unfortunately it doesn’t work anymore :/
On power up, there’s plenty of hum coming out of it, flashing input and solo leds, scratchy pots and faders, silent channels, etc….
I guess it’s a power issue, either in the PSU or in the desk itself. Looking at the components, it’s packed with cheap chinese electrolytics capacitors, but apart from those the rest is standard thru-hole resistors, ceramic or mylar caps with NJM 4580 SIP package dual op-amps (still available at mouser).
So my best bet is that some electro caps have rendered their last breath and shorted the rails…
The adventure begins….