Fender Rumble 500 Power Supply Issue

[Bryan]

I'll check the values on R252-254 again.
Since the voltages on the rails are incorrect what voltage do you think I should I be looking for on the op amp outputs? I assume you are specifying the audio outputs of the op amps.

[Bryan]

I'll check R252-254 again. With the DC rails out of balance, what voltages should I be expecting at the op amp outputs........I'm assuming we are talking about the audio outputs.

[x-pro]

Yes. The audio outputs should be at or near zero.
If any of them has a different value, it should be unsoldered. After each unsoldering operation, check the supply voltage +/-15. At the outputs of 13700 and detector chips the voltages may be very different from zero. Do not touch them yet.

[Helmholtz]

Make sure to measure close to zero Ohm between grounding points of power supply and amp.

[g1]

Yes, ground points are critical as Helmholtz mentioned. Where are you connecting your black probe? You might want to recheck with black probe connected to control board ground.
Also, was the Rumble 100 you compared to also a V3? The older versions gain pot worked different like x-pro stated.
In any case, the Rumble 500 V3 gain should not kill the signal when turned all the way down. The Master does that job. The owners manual (attached) explains what the gain pot should do.

[Bryan]

I locked myself out of the forum for a bit.
Thanks for the manual. Not sure of the version for my working Rumble 100.
I have the control board ground strapped to the chassis ground with the black probe on the control board ground.
After some pretty whacked readings on the op amps I pulled U1-U11 and still got unbalanced supply voltages............until I pulled the fan circuit. Then the supply voltages came back to +/-15v.
I should have pulled the fan in the first place.
I still have some components to put back in. I'll let you know if I manage to get all of chips soldered properly. Should be fun. Then I can check the supply voltage with and without the fan circuit.

[nevetslab]

I was about to suggest it could be our old nemesis solder joint issues lurking about but lifting the fan load on the supply sounds like you re on the right track. I’d have to dig thru my past maintenance records to find when and what I had written in my service notes. I know there are a couple of the Fender rumble 500’s there and they have come thru my shop.

watching with interest!

[Bryan]

I'll try to get time tomorrow. As for my Rumble 100 turning off the audio, you are completely correct. On closer inspection the R23 does not turn the audio off although I thought it did.