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-   -   Zapco Z400C4-SL... Not Again! (http://www.diyaudio.com/forums/car-audio/218425-zapco-z400c4-sl-not-again.html)

90scaraudio 23rd August 2012 11:20 PM

Zapco Z400C4-SL... Not Again!
 
Hi All...
Picked up my second broken Zapco! Must be a glutton for punishment...Anyway... first thing I did was to look at the mess that those 4 caps make when they leak. Well, only one leaked, the far left side. Want to say it's channel one, or left front channel. Pulled all 4 caps then started to clean. When I was brushing around the leak area, one SMD res and semi came off. That's corrosion at work! I replaced the caps and some other 10uf caps, put it back together and tested it. (I think I was the first one to take the amp apart since factory). When it turns on, the idle current is about 1.75amps, good so far. The rear input clip light stays on with no other lights on except the green on light. Then after about 4 second it goes into protect mode and starts the process over. There is negligible dc voltage at the speaker outputs, could be my meter, guess I should have a look at it with a scope, and the front end semis and finals look nice with no shorts.
My Question is does anyone know if the input clip circuit is after the op-amps and after the front end, before the finals? The Soundstream amps have it before the front end boards, after the op-amps.
Guess I could half split it and I haven't ruled out that NAND gate. I'll play some more and write what I find.
BTW. this is scott-leanne that did the post on one of these years ago and I cant remember the password or email address I used the last time I posted.

OK... I replaced the 10uf cap next to the NAND gate pins 12 and 13 with a 100uf for now until I can order some new gates. Next I wanted to see any dc voltage on the spk outputs with a scope. I turn the system on and the rear input clip light comes on along with the power on green light, Idle current still good, then it goes into protect and stays there. It does not try to restart, that tells me the NAND gate is flakey. I think I found one possible problem with the scope.
When the system is on for 4 seconds, the dc voltage on ether rear channels is about .3 volts or less. While its going into protect, the left rear spk output goes to about 5vdc. None of the other channels do this. Am I on to something? Guess I need to pull the finals out of circuit and check them or should I dissect the front end and possibly op-amps for this channel?
Any body??? Suggestions???

:magnify:

90scaraudio 24th August 2012 02:00 AM

1 Attachment(s)
Here is what the old SS reference clip circuit looks like...

AKHeathen 24th August 2012 11:33 AM

if i have learned anything about old school soundstream is their individuality and weakness/strength is all one in the same. unless someone has verified similarities in this amp, i would look at more similar amps. however, in a soundstream, it monitors the voltage differential between the rail and output. speaking soundstream, if outputs are okay, then the first place to look would be the feb connections (with a meter probe, not just naked eye)
however, this is zapco..... what is the voltage to/from the drivers giving 5v? ".3 or less" is fine by me, but 5v is substantial, and certainly a/the problem. you have the board in fromt of you and 3 good channels to compare...

90scaraudio 24th August 2012 08:02 PM

When the system is on for 4 seconds, the dc voltage on ether rear channels is about .3 volts or less. While its going into protect, the left rear spk output goes to about 5vdc just for a split second. None of the other channels do this.
Should have added this..

The last one of these I mest with, none of the finals were bad and its not too fun pulling them out. I will post more on what I find. I'm going to start on the op-amp/pre-amp area first.

AKHeathen 24th August 2012 11:02 PM

does your amp have the delayed turn-on, utilizing a source mute? i don't know the circuit of your amp, but there could be a bad capacitor in that channel, allowing a normally harmless dc signal to pass, and initiate protect.

90scaraudio 25th August 2012 01:52 AM

It has some caps on the balanced input section. It does have delay turn on. I hope it's one of the op amps. Its hard to catch the DC because it only stays on for 3 or 4 seconds. I'll post what I tried and what I found.

AKHeathen 25th August 2012 03:14 AM

i suppose it kills rail voltage, and thus the pre-amp power when in protect, making it hard to find the dc source. i would venture to say it should be present in the 4 seconds if before the mute circuit, and show up if after. it may be possible to keep mute active to test further.

90scaraudio 25th August 2012 03:23 AM

Correct... Sometimes its faster to just replace than to TS. Have you seen the inside of these?
The last one I did is on an old post with pics under the user name; scott-leanne. Have a look.

AKHeathen 25th August 2012 01:05 PM

looks as bad as x-taint and J-gaLo amps to work on. anyways... what;s up with the soundstreams, 'ole buddy, 'ole pal?

90scaraudio 25th August 2012 01:18 PM

1 Attachment(s)
Don't have a problem with Soundstreams... Fixed quite a few....:D


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