Sunn Alpha six repair

[sunnshy]

Hello all. I'm new to the forum. I just received a Sunn Alpha Six PA mixer from a friend. His Dad gigged with it for 25 years but it finally quit working. He was going to throw it out, but knew I was a tinkerer and a musician. So now I have an Alpha Six which turns on (red power light showing) but makes no sound whatsoever with a speaker and microphone hooked up. The thing I find strange is that as soon as you turn it on, whether you have a mic plugged in or not, the "clipping indicator light" comes on and stays on. I lean toward thinking that whatever is causing that phenomenon is the culprit for the overall problem.

I opened up the case and looked around inside. All of the fuses are good (I found three total) and I didn't see any signs of burnt wiring or blown capacitors. All connections seem solid. Any connection that doesn't require soldering, I disconnected and then replaced in case something was just loose. So far no dice. Any ideas?

Thanks a million,
Sunnshy

[loudthud]

The service manual is here: http://sunn.ampage.org/site/svcmans/alphaPA/

Check Q1 and Q11 to make sure you have the +/- 15V.

[sunnshy]

Thanks for the advice. I'm having a little trouble finding the Q1 and Q11 transistors, the manual schematics are a bit hard to read, some of the scans are a little grainy. Where should I be looking in the box?

Thanks,
Sunnshy

[loudthud]

Those schematics in the manuals are impossible to read. I don't know who posted them.

Q1 and Q11 are on the power amp board. They are TO-220 package transistors. They could use small heat sinks if you can figure out a way to mount them. Be sure to check the resistors in series with the collectors.

Check the last post in this thread: http://sunn.ampage.org/sdp/index.php/topic,4634.0.html

[sunnshy]

Alright! I've got some info. The q11 transistor is reading +/- 14 which is probably close enough. The Q1 however is reading right around or just under +/- 1. I'm somewhat of a novice so I'm not quite sure what you mean by check the resistors in series. But does the info provided help you at all?

Thanks,
Sunnshy

[loudthud]

This really isn't the forum for step by step instructions for novice technicians. You need training and the proper tools to repair this type of equipment. Otherwise, you could easily do more damage to the mixer than it is worth. Find someone who has experience soldering on printed circuit boards to help you out.

[Rex B]

Sunnshy. Where are you located?