The client brought me some documentation describing troubleshooting.
It says the control modules can function as a voltage amplifier without the output modules, provided there is no load. Relevant page attached.
I've removed the short between Q10-11.
Power modules removed. No load. Plugged directly into the wall. No DBT or variac.
30VDC on the output, and it goes up to 50V when I short the RCA input jack.
Tried changing all the small diodes, even though I'd checked them before. No change.
Tried changing C30/31 since the document said high offset could be caused by leakage here. It also said C29/32 could be at fault but I don't have any 100pf caps on hand.
The decoupling capacitors, 0.1uF between the power rails and ground on the control module I added at the suggestion of an earlier post are still in place.
As requested in the above post, Q2/3 base voltages are 30V.
~1.2V across R115/120 (47ohm)
Q10 base: 30V
Q10 emitter: 29.3V
It says the control modules can function as a voltage amplifier without the output modules, provided there is no load. Relevant page attached.
I've removed the short between Q10-11.
Power modules removed. No load. Plugged directly into the wall. No DBT or variac.
30VDC on the output, and it goes up to 50V when I short the RCA input jack.
Tried changing all the small diodes, even though I'd checked them before. No change.
Tried changing C30/31 since the document said high offset could be caused by leakage here. It also said C29/32 could be at fault but I don't have any 100pf caps on hand.
The decoupling capacitors, 0.1uF between the power rails and ground on the control module I added at the suggestion of an earlier post are still in place.
As requested in the above post, Q2/3 base voltages are 30V.
~1.2V across R115/120 (47ohm)
Q10 base: 30V
Q10 emitter: 29.3V
I have figured this one out. I sat down with it and said to myself "The only thing this could be is something that is so simple and stupid I'll never forgive myself for missing it this whole time!"
And the issue was someone had replaced the input jacks and isolated the replacements from the chassis when they were not supposed to be isolated.
And the issue was someone had replaced the input jacks and isolated the replacements from the chassis when they were not supposed to be isolated.
