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Witwe 9th February 2013 11:28 AM

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:

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)
Can you help me with this?

-> I found out that Q309 is getting hot.

Perry Babin 9th February 2013 07:13 PM

What is the PC number for that amp?

Lift 2 legs of D302. Does that allow the amp to produce clean audio?

Witwe 11th February 2013 11:48 AM

and yes, it does!

Perry Babin 11th February 2013 06:19 PM

Carefully check Q315, 316 and 317.

Witwe 12th February 2013 06:10 AM

they are not shorted.
should I test something special?

Perry Babin 12th February 2013 07:23 AM

When the diode was in the circuit, was the signal distorted when there was no speaker or dummy load connected to the channel?

Witwe 12th February 2013 09:45 AM

yes, without load connected, only the oscilloscope.

Perry Babin 12th February 2013 10:16 AM

One of those transistors is likely leaky if it's not shorted.

Witwe 12th February 2013 11:47 AM

OK, I will change all 3 of them and give you an update.
thank you!

Witwe 13th February 2013 07:30 AM

even after changing Q315 Q316 and Q317 the signal doesn't look better. :(

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