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Old 2nd January 2012, 08:23 PM   #1
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Default Rockford Fosgate T-15004

I recieved this amp in for repair.

The left rear channels had DC voltage on the output terminals and the right rear channels had alot of distortion.

I found 6 output fets shorted and 6 source resistors burned to a crisp.

I replaced the 6 output fets and the 6 source resistors. I replaced 6 gate resistors. I found numorous smd resistors out of tolerance and replaced them. I replaced 3 pnp and 3 npn drivers the PZTA56 and PZTA06. I found two 22.1 ohm resistors out of tolerance which were linked to the drivers.

The right rear channels produce audio now but the left rear still has bad distortion. There are about four 5D smd diodes that are linked to the drivers as well. Just wondering if those should be replaced.

I am not familiar with these amps and unsure which are the protection transistors. Wanting to see if I could remove something to get rid of the distortion.

Any clues as to where to look?
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Old 2nd January 2012, 09:36 PM   #2
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Post a photo of the distorted sine wave output with a load connected to the amp.
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Old 3rd January 2012, 03:38 AM   #3
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The area thats giving me problems is the 4 series area. I posted a pic the first pic is of the problem area.

The second pic is of the waveform on the left rear channel.

I can make a list for you of all the parts I have changed if it would be helpful in troubleshooting for you.

One thing I thought I would mention when the head unit is turned to half volume there is about 3.657 vdc on the channel, turning it any higher causes my meter to bounce between 3.657 and OL
Attached Images
File Type: jpg T15004 output 002.jpg (1,022.8 KB, 59 views)
File Type: jpg T15004 output 001.jpg (794.8 KB, 59 views)
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Old 3rd January 2012, 10:17 AM   #4
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Was that with a load?

Does the bias control work?
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Old 3rd January 2012, 09:59 PM   #5
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Yes that was hooked up to a small 4 ohm speaker at low volume.

The bias control does not work.
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Old 4th January 2012, 01:47 AM   #6
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Removing D4002, 4003, 4004 and 4005 will defeat the protection circuit (like you've done in the smaller amps) to see if it will produce audio. I don't know if it's safe in these amps.
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Old 4th January 2012, 06:12 AM   #7
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Well since the outputs failed and the source resistors looked like burned hot dogs the protection diodes have probably failed anyway wouldnt you agree?

Whats the worst that could happen?
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Last edited by seankane; 4th January 2012 at 06:14 AM.
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Old 4th January 2012, 10:21 AM   #8
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I replaced D4003, D4004, D4005 and the amp seems to be working. The audio is clean from what I can tell.

The bias control is now working too. I guess the problem was the protection circuit?

I didnt replace D4002 because I am unsure what it is. It has the marking JS but when I look it up it doesnt come back as sot-23 package.

I am not sure if it needs to be replaced or what a good sub would be or even the correct replacement would be.

Any thoughts on D4002?
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Last edited by seankane; 4th January 2012 at 10:23 AM.
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Old 4th January 2012, 05:12 PM   #9
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BAS21LT1 according to the schematic diagram. I wouldn't replace it if it's not defective.
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Old 4th January 2012, 07:19 PM   #10
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Ok I will leave it alone, wondering if you could e-mail me the schematic. I have another one of these coming in the next few weeks.
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