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Old 29th April 2008, 06:53 AM   #1
KyferEz is offline KyferEz  United States
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Question Kicker ZR1000 repair help needed

I've got this amp that had burned supply fets. I've replaced them but if I power up the amp it immediately draws >20Amps. So I disconnected the output of the transformer from the amp board, and the current draw dropped to less than an amp and I get 120VAC across the output of the transformer.

So, with power connected, if I attach either output from the transformer to the PCB current draw jumps again.

I've checked the output transistors, and they all seem Ok. No shorts, and diode check passes on them. I've checked the rectifiers and they are Ok. I don't have anything hooked up to the rca inputs or to the speaker outputs. What should I check next?

Thanks!
KyferEz
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Old 29th April 2008, 07:26 AM   #2
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Clamp the transistors to the sink to prevent damaging them while troubleshooting.

Have you checked all of the gate resistors for the power supply FETs?

Have you tried turning the bias control down to see if the current draw dropped to normal?

If that doesn't work, measure the voltage across each of the emitter resistors while the amp is powered up. With the bias set low, there should be essentially no voltage across any of the emitter resistors. If you find one or a group that have more than ~0.001v (with the bias set to the minimum position), it will help you determine where the fault is. If you have a large 2 ohm resistor, insert it in the B+ line to help prevent damage to the amp while troubleshooting.

Most of the ZR1000s I've seen had no fuse in the RCA shield circuit but a few were modified. To confirm that the shield ground is intact, measure the resistance from the input RCA shield to the transformer's secondary center tap. It should be ~0 ohms.
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Old 29th April 2008, 08:20 AM   #3
KyferEz is offline KyferEz  United States
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Gate resistors for the FETs are fine.

I'm not sure what you mean by setting the bias low. I do see some pots in the amp circuitry, but don't know which way to turn them to set the bias low? How do I figure this out?

In any event, I tested all of the emitter resistors with the amp powered up and the transformer secondary reconnected. None of them had any voltage across them.

This ZR1000 does have the fuse. Connection from shield to center tap is good.

Thanks!
KyferEz
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Old 29th April 2008, 08:52 AM   #4
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If there is absolutely no voltage across any of the emitter resistors, the problem is not likely in the audio section unless you have defective insulators.

You may have a shorted inductor. With the amp on, twist the inductor/move the windings to see if the current draw drops.
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Old 29th April 2008, 05:10 PM   #5
djQUAN is offline djQUAN  Philippines
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sorry to threadjack a bit....

Perry,

I bought a broken ZX1000.1 amp and it has all PS fets burned, output fets seem OK, all drivers don't seem to be burned. what started it seemed to be the output inductor which is black and really toast. I was wondering what is the inductance value of this as I intend to replace it with an MPP core of the same size as I think the heat could have permanently changed the core characteristics and have some MPP cores coming my way. also, will this amp be safe to test run without a sink?
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Old 29th April 2008, 06:27 PM   #6
KyferEz is offline KyferEz  United States
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I've got good news and bad news.

The bad news is that while I was testing the amp, something in the audio section went pfffzzit and I smelled the magic smoke. The high current pull dropped down to less than an amp, and then started ramping up. Now the protect light comes on and the outputs get hot over the course of a minute or two.

The good news is that the supply now outputs a good +55V after the rectifiers! So whatever was causing the short seems like what fried.

So I've got no idea what burnt. I do know the general area of the part that burnt... What now? Test all of the smaller transistors?
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Old 29th April 2008, 10:37 PM   #7
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With a high power lighted magnifying glass, you should be able to find the burned component. It could be any type of component so don't limit the search to transistors.
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Old 30th April 2008, 03:13 AM   #8
KyferEz is offline KyferEz  United States
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I've looked and looked. I can't find anything visibly damaged except for a 36k smt resistor that looks like it has gotten hot, but it's fine.

Edit: could the original problem have been caused by one of the supply's filter caps??? I just noticed one is swelled on the top and I don't think it was before.
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Old 30th April 2008, 03:36 AM   #9
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So I don't forget... After you find all of the problems and have replaced all of the defective parts, you should push, pull, twist the winding on both the power transformer and the inductor while monitoring the current draw to make sure that none of the windings are intermmitently shorted. I've see this problem often in the ZR series amps.

Are the outputs in 'both' channels heating up?

If so set the bias pots for minimum idle current from the power supply.

If only one channel is getting hot and the bias pots are set to the minimum, begin your search for defective parts in the channel that's getting hot. Shorted or leaking drivers are the most likely cause for excesive current draw (if the output transistors are not shorted or leaking).

It's possible that the capacitor was shorted and was causing the excessive current draw.
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Old 30th April 2008, 03:16 PM   #10
KyferEz is offline KyferEz  United States
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Only one side is gets hot - the side that didn't have smoke come from it...

I wiggled and pushed and pulled as much as possible on the transformer and inductor (they're gluded down pretty tight) and nothing changed.

The side that had smoke come from it stays cool.

I found schematics for the amp here: http://www.schematicsforfree.com/arc...ice_Manual.pdf
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