rockford fosgate 700 S

mike49504 · 26th June 2010, 07:46 PM

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.

26th June 2010, 07:46 PM	#1
mike49504 diyAudio Member Join Date: Sep 2006	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?

26th June 2010, 08:16 PM	#2
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	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. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

26th June 2010, 08:52 PM	#4
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	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. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

28th June 2010, 10:43 AM	#6
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	R217 is a 47 ohm resistor. If that resistor opened, Q207 and Q205 should be checked. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

28th June 2010, 11:16 AM	#7
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	If Q205 is defective, Both Q205 and Q204 must be replaced with matching transistors (matching date codes). __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links


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26th June 2010, 08:38 PM	#3
mike49504 diyAudio Member Join Date: Sep 2006	Lifted 202 and 205 No difference still distorted. I checked the voltage across emitter resistors all read 0 volts.

28th June 2010, 03:02 AM	#5
mike49504 diyAudio Member Join Date: Sep 2006	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?

28th June 2010, 05:19 PM	#8
mike49504 diyAudio Member Join Date: Sep 2006	Are Q204 and Q205 2A's?

28th June 2010, 05:35 PM	#9
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	Yes. MMBT3906. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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