# Zapco z150 repair help



## fatman406 (Jul 19, 2009)

Soooo I picked up a Zapco z150 at a Swap Meet today in pretty good cosmetic condition for $60 thinking I made an Old School score... Well there is heavy distortion in the right channel and the guy I bought it from said "it has like these special knobs inside it to turn up the bass YO". I should have just walked away but it just i bought it anyway and it turns out those "Special Knobs" were the bias adjustment knobs :facepalm:

so the left channel is clean and clear so that leave me to believe he bridged it to the right channel and messed with the right channel bias adjustment and now its way off, OR bais is fine an the output transistors need to be replaced.

My day job is arcade machine repair so im adept a soldering, just audio isint my strong suit and I want some leads. Any help would be appreciated

Also move this thread if its in the wrong forum

(edit: sorry for the crap pics, all I have is a potato to take pictures with right now)


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## fatman406 (Jul 19, 2009)

now after some time left side went out, now both channels sound like crap 

(edit)
It seems that when both channels are connected, left channels sounds perfect but right channel has large of Distortion that sounds like a full range wizzer cone speaker under large amounts of excursion trying to produce high end. But when only a single channel is connected to the left output or when connected mono properly there is distortion.


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## ATOMICTECH62 (Jan 24, 2009)

You need an oscilloscope and a high frequency(50khz)test tone to set the idle bias correctly.
OR.Guestimate and set it with 5-10mv across the emitter resistors.

You may have already damaged the output transistors.


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## TrickyRicky (Apr 5, 2009)

First of all I would start by removing the filter and rail capacitors, THESE LEAK and have leaked and have open traces below them. Those traces need to be repaired first before trying to trouble shoot the amplifier any further. 

I recommend FC or FM from Panasonic, available pretty much everywhere (mouser,digikey,arrow). Good luck.


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## fatman406 (Jul 19, 2009)

Thanks for the replies guys!

ATOMICTECH62: I have access to an o-scope but i need clearance to use it and i doubt that they'll let me use it for personal reasons but ill try, if not then ill just have to hope i set it right using the multimeter method.

Also I kinda suspected that the output transistors were fried so I ordered a set of SM micro TIP35C and SM micro TIP36C transistors.

TricyRicky: I guess I was already a step ahead of you cuz a couple of caps were out of spec and I ordered a set of Caps For the Rail And Filter sides of the amp already and a couple of odd ones too. This amp is old! 23 years to be precise, its as old as I am! so recapping the amp was already planned seeing that caps don't age well. I got a set of audio grade Nichon Capacitors. I will inspect the board for traces of corrosion and damage to the traces and will repair if necessary.

I will report back with findings after I get done and we will find out if I got a keeper or a fancy paperweight! 

BTW thank you very much for the tips!


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