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Is the "81 130" block on the schematic a separate PCB which can be unplugged?If so you could inject a signal on the output (pin 1) of the module and measure the B2 signal (when the appropriate switch is on). From the schematic there will be about an 11:1 attenuation (set by the R020 / R021 ratio) so if pin 1 is 300mV it will be about 27mV at B2.There will be attenuation of the signal between the R034 wiper and the R035/R036 junction, because R036 is being driven from a low-impedance source (Q003 emitter) so R035/R036 form a voltage divider. So if you're seeing 40mV at B3 when there's 600mV at the I002 output, that's not wildly wrong._Edit:_ Ah - ignore that - I see you found the problem!
Is the "81 130" block on the schematic a separate PCB which can be unplugged?
If so you could inject a signal on the output (pin 1) of the module and measure the B2 signal (when the appropriate switch is on). From the schematic there will be about an 11:1 attenuation (set by the R020 / R021 ratio) so if pin 1 is 300mV it will be about 27mV at B2.
There will be attenuation of the signal between the R034 wiper and the R035/R036 junction, because R036 is being driven from a low-impedance source (Q003 emitter) so R035/R036 form a voltage divider. So if you're seeing 40mV at B3 when there's 600mV at the I002 output, that's not wildly wrong.
_Edit:_ Ah - ignore that - I see you found the problem!
