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Bose 901 series V equalizer - anyone have a schematic?

S

special_20

Active Member
Hello, I have recently acquired some Bose 901 series V speakers, stands and equalizer. Sadly I didn't get a chance to test before I bought. The equalizer seems not to be working - when I depress the "monitor" switch, It does not seem to engage the equalizer circuit.

I am trying to trouble shoot but have not been able to find a schematic. Anyone by chance have one or know of a source?

Anyone have experience trouble shooting these boards?

I am getting low/no sound out of both channels.

Diagnostic work to date:
  • When plugged in I get power and see LED light up
  • I have confirmed I'm using the "amplifier" inputs and ouptuts on EQ
  • With eq connected to amp via amp's tape monitor circuit, and the amp's tape monitor button engaged, I get almost zero output form speakers (I have to really crank it to get any volume)
  • With the amp tape monitor disengaged I get full volume
  • The monitor button does not alter sound/volume
  • This is on both channels
  • I have tried 2 different receivers with the same results
Attempts at repair
  • Disassembled and cleaned "monitor" and "bass" switches. They look and test good
  • Inspected solder connections
  • Applied fader lube to slide switches; checked with ohm meter and seeing good contacts.
  • Replaced all electrolytic capacitors
  • checked voltages on power supply and am seeing 35 vdc at test points on board and at filter caps
  • Seeing voltage on all 3 legs of transistors in power supply
Any thoughts or suggestions for next steps? I'm thinking IC's are next but would love a diagram to check voltages
 
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whoaru99 said:
You're 100% sure the EQ to Tape Mon loop is hooked up in the right directions?
Click to expand...
Following schematics from user manual. I'm using the "amplifier" connections. I'll try to get some pictures later today. I did at one point swap inputs and outputs at amp and there was no change.
 
The receiver/integrated amp doesn't happen to be one that has separate record selector that you also have to switch to the source input?
 
aaand I played around a bit more today. I pulled the amp out of the stack so I could actually get a good look at everything. Using pre out / amp in connections I've been able to get this thing working. I ended up reversing my connecitons from how I had originally connected in. I'm guessing that was my original issue.

Thread closed :)
 
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