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.

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[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.

 

[fongman]

I'm a little confuse but, i'd test the top left and right pin. tested okay. next the right top and bottom right. and around and found none shorted.

 

[tsmith1315]

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.

This statement is confusing. Could you clarify?

 

[fongman]

The amp turns on fine without any voltage draw. I notice that the input on the RCA have low ground when the amp is trun on. I apply or put gound to it and the amp would go into overload. After 10 sec it would come out of overload. Still no sound. Thanks i hope you can help?

 

[tsmith1315]

The Z220 has balanced differential inputs, so the RCA shields aren't grounded...

 

[fongman]

Thanks, do you think it will be an easy fix?

 

[fongman]

Hi guys, i just want to update that the amp was fixed. I found out that the input RCA are bad. I resolder both side and now the amp plays fine. I want to thank those of you who help me in anyway.

PS
Perry thanks for all you time and support