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-   -   rockford fosgate 700 S (http://www.diyaudio.com/forums/car-audio/169373-rockford-fosgate-700-s.html)

mike49504 26th June 2010 07:46 PM

rockford fosgate 700 S
 
I replaced 2 IRF9540's in this amp the emitter resistor and a 52 ohm resistor

I also turned the bias pot down Amps left channel still distorts like crazy.

Wondering where i should go from here?

Perry Babin 26th June 2010 08:16 PM

Lift D202 and D205 to see if that allows it to play cleanly. Lift one, then listen to it. If it's still distorted, lift the other.

mike49504 26th June 2010 08:38 PM

Lifted 202 and 205 No difference still distorted. I checked the voltage across emitter resistors all read 0 volts.

Perry Babin 26th June 2010 08:52 PM

Are the two 20 ohm resistors (R262 and R263) in tolerance?

Are the driver transistors (Q229 and Q230) OK?

The schematic diagram lists the outputs as 9640s, not 9540s.

mike49504 28th June 2010 03:02 AM

All of them check fine.

I found resistor R217 burnt but cant make out the markings DO you know by chance what value it is?

Perry Babin 28th June 2010 10:43 AM

R217 is a 47 ohm resistor. If that resistor opened, Q207 and Q205 should be checked.

Perry Babin 28th June 2010 11:16 AM

If Q205 is defective, Both Q205 and Q204 must be replaced with matching transistors (matching date codes).

mike49504 28th June 2010 05:19 PM

Are Q204 and Q205 2A's?

Perry Babin 28th June 2010 05:35 PM

Yes. MMBT3906.


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