SUNN Coliseum 300 Problem

[cupomeat]

I had a Coliseum 300 for about 15 years now and it has been great except once when a Capacitor lead broke off. However, I now have this problem that I could use some help in troubleshooting.
The Preamp section works great (I get clean signal out of the Pre-Out), However, the Power Amp Limit light glows faintly and I have only a hum out of the power amp outputs with no sound output.
I have disassembled it looking for the obvious loose connectors, etc. but thought I'd seek guidance before digging deeply.
Any suggestions would be very helpful! Thanks
Eric K.

[Don T.]

Hello:
 Well your power amp either has bad filter caps or you have a shorted output transistor. Check the speaker outs with a voltmeter and check for DC offset. It should not have more than 50mv of DC voltage reading there. Because you say the preamp works ok and it receives its +15 & -15v from the power board it would indicate that you don't have a full cap failure. There are also two shunt diodes connected to the output that may be shorted if the transistors check OK. Check the power supply fuses when you get it opened up (located on the tranformer end of the board). Open her up and look around and tell me what you find.
Don T.

[cupomeat]

THanks for the advice. I started to perform the troubleshooting you suggested when I noticed that my other 4700 micro farad 63v capacitor had broken off its lead. So, I am in search of that capacitor (seemingly very difficult to find) before I can properly diagnose if the amp has any other maladies.

Thanks again and stay tuned.

Eric K.

[Don T.]

Hi,
 Actually those caps should be easy to find. They are pretty popular. I have a few spares if you come up empty locally.
Don T.