rockford 800a2 fried channel help .

[ethridgeruby]

OK... i have a rockford 800a2 one chanel quit working. i opened it up and took my B&K transistor testor and tested that 10 transistors are bad. five IRF640 and five IRF 9640. I replaced them as well as the 10 gate resistors. i was really sure this was all that needed replaced.
well i hooked it up to my aston power supply. all 10 of the transistors i replaced fried within 30 seconds. they got super hot super fast. I Get a voltage reading of around 45+ volts form this speaker output. the working channel I get .3 volts. I am lost now. does anyone have any insight on this.

 

[Dr. Photon]

check the driver stage, predriver stage, and the bias circuitry. Sometimes the bias circuit opens up and the output stages basically shorts out. For testing, you might want to consider using a large lightbulb (headlights?) in series with the power supply and/or a small fuse (like a 5 amp one).

 

[zagisrule!]

FYI: Fosgate uses what appeared to be a gained output stage, biasing to the rails as P-channel is on top rail and N-channel on bottom. The normal bias will measure little shy of the full potential across the rails.







-Matt

 

[Jocko Homo]

The last time that I did a buddy a favor by working on a dead Fosgate, they e-mailed me the schematic. Very helpful folks, at least back then. Would not hurt to call and see what service info they will supply. Any is better than trying to fix one with none.

Jocko