Sunn Beta Bass preamp troubles

[sunnuser]

Hi, new here and I have a Sunn PB-10 (Beta Bass preamp only) I am having some issues with. Here is the schematic:
http://sunn.ampage.org/site/svcmans/...tamanual18.jpg
http://sunn.ampage.org/site/svcmans/...tamanual19.jpg

The trouble I am having is a starving output. The output is severely gated and IC112 is heated up really fast upon turning the unit on. I have checked the diodes in that filter of IC112 as well as checked all of the components in that section. I tried disconnecting each channel to see if that would draw less current but the opamp is still heating up fast! All of the connections are properly soldered but to no avail, the problem persists. Channel A is much louder than Channel B after about 30 sec of power, Channel B volume seems to drop significantly after that initial 30 seconds. I have tried swapping the IC112 out with another known good one too.

So overall what is happening is, Channel A and Channel B are both gated and only respond when the strings of the bass are hit fairly hard, then the signal just gates and sizzles away. IC112 is overheating no matter what I do. I have checked the output jacks to make sure they are not shorting, they are fine. Any help would be great!

[Jazz P Bass]

Just a suggestion.
Get Cute PDF Writer.
You can save jpg files as a pdf.
It sure makes it easier to zoom in on a schematic.
The best part is that it is free!
Link: CutePDF - Create PDF for free, Free PDF Utilities, Edit PDF easily;.

[Jazz P Bass]

How about disconnecting the link from Channel A & Ch B to IC112.
Insert an open plug into both A & B " From Accessory" in jacks.
That should disconnect the A from B link.
Then remove IC112. (you do not have reverb, right?)
Check both + & - power rails for stability & lack of any Vac ripple.
Now you can test the two channels independently.
Use a scope or a DVM set on Vac & trace a signal through each circuit.
See where the signal is failing.

[gbono]

Check the +-15 supplies on the power amp board.

[DrewV]

I have a Beta Bass that appears to have the same symptoms. Upon taking a line out from (any one of ) the accessory panel jacks, I found that the preamp signal was clean. To double-check I ran a line into the power amp in. It displayed the same distortion characteristics as the instrument input did.
Why would I get a clean preamp out signal at the FX send if the problem is in the preamp board and then, why is the power amp in signal ( bypassing the inst inputs) all blown out too?
The voltages on the emitters of Q1 and Q11 are way off. Q1 gets extremely hot!!

[loudthud]

While U112 is removed, check for a shorted diode at the output. Also those 2.2uF non-polar caps have frequent failures. The MC14506 is very difficult to find. I hope it's not bad.

[DrewV]

Q7 ended up being bad, so only half the output was being amplified. I also replaced R25 & R52 as well as C1. The resistors were out of spec and the cap was iffy. Thanks DrewV