PA Head, power/no sound. where to start?

[jeffz63]

Hello,
I would like to get some input from the forum on this head I have. It's a Zebra Zm-0812 8 channel.
It powers up just fine but I get Zero audio. No pops when powered on, nothing. I tried connecting my cd player into the tape inputs, nothing.
I would like to add, I looked at the output IC's and they look ok and there is no burnt smell. Everything looks fine everywhere. Is there an internal fuse or something?
I took several pictures. You can view them HERE I didn't take any of the front panel with all the knobs, etc. but I certainly can if you need me to.
Thanks in advance!

 

[ronsimpson]

In trouble shooting it is good to break things down into small pieces and test each.
It sounds like the lights come on so part or all the supply is ok.
Can you feed a signal in and get it to come out? I think "effects send" is a low level output.
I just want to know if the problem is in the power amplifier or in the mixer part.
Is this what you have?

 

[ronsimpson]

In this picture on the right side there is a thermal switch. It will turn off the power amplifier if the heat sink is too hot.
Do you have a meter? With the power off can you measure the resistance of the switch? OR With the power on what is the DC and AC voltage on it.

 

[jeffz63]

Thanks for your help. Yes, That's the exact PA head I have. The component with the red and yellow wires is what you are referring too right? I have to step out for a few hours. When I get back I will try the effects send and see if my landlord has a working meter. Thanks again!

 

[ronsimpson]

The thing with the red and yellow wires is a thermal switch and should be on (closed) when cool. When hot it opens. I think when it cools off, the thing will go back to on.
Worth a try.

 

[jeffz63]

The thing with the red and yellow wires is a thermal switch and should be on (closed) when cool. When hot it opens. I think when it cools off, the thing will go back to on.
Worth a try.

The head never gets hot because it doesn't work. Well, it powers up and the fan works but there's no audio coming out of the speakers. What would be best to plug into the effects send to test that way? Its a 1/4" input so would maybe a guitar work? I'm going to try and get a multimeter tomorrow. Is there a way to bypass the thermal switch temporarily just to see if that's the culprit?