This was an interesting repair job. A Bose 901 Series I Active Equalizer, second production run, came through the shop. There was no identifiable serial number, and the switches were all screwed on behind the faceplate giving it an odd bulky appearance. Most of the wiring had been replaced and there were broken wires and wiring errors. The owner reported buying it on eBay and sending it in for service without testing it. I can’t imagine it would have worked well in its initial condition.
Fortunately, after correcting all the wiring errors and replacing every part on the board with some upgrades, it’s actually as good as new!