Zapco Z220 no sound?

[fongman]

I just bought a old school Zapco amp. I was happy to find it but the sad news is that it has no sound. I just don't know what is wrong? Amp power up fine. I measure the amp rca and got only .500v. I know i should be getting 12v, but when i apply ground to it the amp goes into overload or protection. Help???what could be wrong??? This is what it looks like.

[I Am An Idiot]

The most common cause of an amp being in protect is shorted output transistors. Do you have an Ohm meter to check for shorted transistors? The output transistors are the 4 larger devices mounted to the heat sink in the top left of the picture, and the 4 devices mounted to the heat sink in the bottom left of the picture.

[fongman]

Thanks, are they the same as rockford fosgate amp? Set to diode? Or ohm?

[I Am An Idiot]

I use Diode test, but either will work. The Rockford has Mosfet output transistors. This amp appears to have Bi-Polar transistors. Finding shorted ones uses pretty much the same test procedure.

[fongman]

I tested the outputs. Im not sure if they are okay. The pin 1 and 3 are short when test with the meter. but pin 1 and 2 are reading .500. All test are done with diode test. Do you think they all are bad?

[fongman]

any ideas perry?

[I Am An Idiot]

What number is the meter displaying when on 1 and 3? The meter may be beeping, but they can not all be shorted.

[I Am An Idiot]

Also check the round component in the middle of the board. There is a square cut out in the board with the round component bolted to the heat sink. Check from one leg to the 2 legs that are 90 degrees from it. Do this on all 4 legs of the device. Do not check from one leg and the leg 180 degrees from it.

[fongman]

I got .066 on the meter on pin 1 and 3

on the middle where the bolt is. I can see on 4 pin. one is neg and pos and the other 2 have nothing. Should i test form pin 1,2,3 on the transistor to the legs on the middle each 4 pins? how do i know if this is bad?

[I Am An Idiot]

Check from one leg of the part to the leg that is 90 degrees to the left of it, and then the leg that is 90 degrees to the right of it. Repeat this process for all 4 legs of the part.