Zapco system 151-A wont power up - diyAudio
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Old 4th August 2010, 08:25 AM   #1
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Default Zapco system 151-A wont power up

I have four of these amps and none of them will power up.Seems like at least one of them would work out of four.I have the hot wire going too the + and the ground going too -,and another hot wire going to the 12 volt out,which seems to be the turn on.I get no voltage reading on any of the 4 prongs next too the 30v out.Thanks for any information.....Robert
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File Type: jpg 151a 001.jpg (432.9 KB, 116 views)
File Type: jpg 151a 002.JPG (738.3 KB, 110 views)
File Type: jpg 151a 003.JPG (784.8 KB, 107 views)
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Old 4th August 2010, 05:20 PM   #2
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Check the fuseholders, they like to have bad contact issues. Other then that, blown power supplies and blown channels were pretty much common place with these old boys.

And as I recall the power supplies were a pain to take apart and reassemble. Its been a while but I have a few of these under my belt.
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Old 5th August 2010, 08:33 PM   #3
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The +12V out is not an input. It was intended to provide 12V for a head unit, that would switch on the amp by drawing current through that lead.

Try connecting B+ and ground only, and check for 12V on the turn on lead. Use a resistor or lamp to ground to draw current from the turn on lead. A couple hundred milliamps should be more than enough to turn it on, be careful not to exceed a couple amps.

BTW, those are not 151's, they appear to be 150L's -earlier than the 151. model # and dates are usually listed with the serial #.

And if you wanna trade them for something else, let me know.
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Last edited by tsmith1315; 5th August 2010 at 08:44 PM.
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Old 6th August 2010, 03:12 AM   #4
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Thanks for the responces,it is possible that I dont have them hooked up right.I cant find an owners manual.I cleaned the fuse holders and there is power going through them.Tim can you describe in a little more detail on how to turn these amps on,I dont quite understand.Thanks Robert
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Old 8th August 2010, 07:41 PM   #5
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Sorry for the delay.

These amps were made in the late 1970's. Headunits didn't have remote outputs then, and not all had a power antenna output. Some that did would lower the antenna when a cassette was inserted. So, instead the head unit's +12V switched power lead would be connected to the amplifier's remote lead INSTEAD of to the factory wiring or fuseblock.

In that way, the amplifier is actually supplying current for the head unit. When you turn on the head unit, it draws a current through the amp's turn-on circuit, and that signals the amp to turn on.

So, you need to draw a bit of current from the 150's turn-on connection. A bulb-type test lamp (not LED-type) may draw enough to do it. Or you can use a 1157-type blinker bulb, or a 5W resistor in the 100 ohm range, or even a head unit.

Or you can just send them to me and I'll send you a big working monster amp in their place!
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Last edited by tsmith1315; 8th August 2010 at 07:45 PM. Reason: habitual editing
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Old 22nd August 2010, 02:23 AM   #6
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THANKS Tim,The test light did the trick.All four of the power supplys work fine at 30dc volts.Three out of five of the amps work fine and sound very good.0ne blows fuses and the last one wont do anything,but they are very old probaly first gen.I am going to install one in my truck for midbass.....Robert
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