Rockford fosgate 400S

[mike49504]

I replaced the power supply fets and the rail caps in this amp.

I get 9 volts on the left channel outputs so i replaced all outputs in that channel And still have 9 volts on output terminals..

Any ideas??

[kds9591]

Check your driver transistors to see if they are shorted. I believe they may be numbered Q2-Q5 near the center of the board. They are SMD transistors marked 1A,2A on case.

[Perry Babin]

If you don't find any open gate resistors, open driver resistors or leaking/shorted/open driver transistors...

If you touch a speaker or dummy load to the speaker terminals, does the DC drop to 0v?

If you allow the amp to remain on for 5 seconds (no load) does the DC drop to 0v?

[mike49504]

All gate resistors measure 10 ohms I replaced the driver transistors and checked the driver resistors all seem fine..

Amp still has 9 volts of DC on outputs.


If i connect a speaker to that channel voltage remains at 9 volts and amp draws excessive current.

If i leave the amp on for 5 secs or longer the voltage remains it never drops

[Perry Babin]

Lift Q109 and Q111. Does that get rid of the DC offset?

[mike49504]

Yes it went away Q106 was defective.. Do you know what part that is??

[Perry Babin]

Q106 is an MMBT3906 but that wouldn't cause it to have DC offset. That's a protection circuit component.

[mike49504]

So what should i check for?? Q106 and Q111 are still removed.

[Perry Babin]

Do you mean Q109 and Q111?

[mike49504]

Yes Sorry