I'm working on a B52 AT212. The gain switch in the overdrive channel is not working. It is stuck in gain 1. Engaging the switch doesn't activate the gain pot, or the volume pot for gain2. It does activate the contour for gain .
Based on the attached schematic, I'm thinking it's a problem with the CTL2 voltage that controls RLY2 and RLY6. When the gain switch is open, it measures about 11V. When the switch is engaged, it drops to maybe ten volts, so I don't think any current is going through the relay to flip it.
So I measured at either side of R91 that feeds the Q5 transistor. The base voltage is always very close to zero, even when the pin 4 of IC11B is at 9V.
I thinking that either Q5 or Q6 is burnt. Does that sound right? Do you guys see anytjing else I should check? I'm trying to debug as much as possible without taking the board out. There are a lot of jumpers and knobs on this amp.
B52 AT100.pdf
Based on the attached schematic, I'm thinking it's a problem with the CTL2 voltage that controls RLY2 and RLY6. When the gain switch is open, it measures about 11V. When the switch is engaged, it drops to maybe ten volts, so I don't think any current is going through the relay to flip it.
So I measured at either side of R91 that feeds the Q5 transistor. The base voltage is always very close to zero, even when the pin 4 of IC11B is at 9V.
I thinking that either Q5 or Q6 is burnt. Does that sound right? Do you guys see anytjing else I should check? I'm trying to debug as much as possible without taking the board out. There are a lot of jumpers and knobs on this amp.
B52 AT100.pdf
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