Rockford Fosgate 800.4 - Distortion Ch RR - diyAudio
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Old 9th February 2013, 11:28 AM   #1
Witwe is offline Witwe  Germany
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Default Rockford Fosgate 800.4 - Distortion Ch RR

Hi there!

I have trouble with the amp of my brother.
He told me that the right rear channel isn't working properly. (much distortion)

When I play a 100Hz Sine wave the RR Channel lookes like this:
Click the image to open in full size.

after a little search I found out that Q323 and Q310 are shorted, the source resistors R380 and R336 are open, the resistors R382 and R383 are open and the drivers Q321 Q322 are shorted.
After changing this parts, the sine wave won't look better
It looks like this on every of the 4 IRF540 (checked at the middle leg)
Click the image to open in full size.
Can you help me with this?


-> I found out that Q309 is getting hot.

Last edited by Witwe; 9th February 2013 at 11:33 AM.
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Old 9th February 2013, 07:13 PM   #2
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What is the PC number for that amp?

Lift 2 legs of D302. Does that allow the amp to produce clean audio?
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Old 11th February 2013, 11:48 AM   #3
Witwe is offline Witwe  Germany
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PC-3095-B
and yes, it does!
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Old 11th February 2013, 06:19 PM   #4
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Carefully check Q315, 316 and 317.
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Old 12th February 2013, 06:10 AM   #5
Witwe is offline Witwe  Germany
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they are not shorted.
should I test something special?
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Old 12th February 2013, 07:23 AM   #6
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When the diode was in the circuit, was the signal distorted when there was no speaker or dummy load connected to the channel?
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Old 12th February 2013, 09:45 AM   #7
Witwe is offline Witwe  Germany
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yes, without load connected, only the oscilloscope.
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Old 12th February 2013, 10:16 AM   #8
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One of those transistors is likely leaky if it's not shorted.
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Old 12th February 2013, 11:47 AM   #9
Witwe is offline Witwe  Germany
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OK, I will change all 3 of them and give you an update.
thank you!
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Old 13th February 2013, 07:30 AM   #10
Witwe is offline Witwe  Germany
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even after changing Q315 Q316 and Q317 the signal doesn't look better.
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