This Bose® 901 Series II Active Equalizer, serial #107915, came through the shop for a repair. The owner reported it was developing the typical age-related problems, so it was time for an overhaul!
This unit was originally designed for European voltages, but had already been converted at some point in the past for the U.S. electric service.
Inside, the main filter caps were looking pretty crusty, and one of the secondary filters had blown an end out. Definitely time for service. And judging from the soldering on the back, these capacitors had been replaced in the late ’70s or early ’80s.
Bose® used very short leads, which have a distinctive crimp which prevents them being pulled back through the front of the PCB which was a giveaway they were populated with an old automatic placement machine. The replacements have longer, bent over leads. They’re all getting replaced anyway, though!
With all new parts and a thorough control and switch cleaning, this equalizer was ready to go home and sound great for a long time to come!