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-   -   Fosgate 501s help please (http://www.diyaudio.com/forums/car-audio/226273-fosgate-501s-help-please.html)

joesch1999 23rd December 2012 05:36 AM

Fosgate 501s help please
 
Are the n channel fets 3205's I thought they were z 40's in this amp there are blown 3205's in it now I can't remember any fosgates with 3205's but maybe they did

seankane 23rd December 2012 05:54 AM

They used IRF3205 in the power supply with a 68 ohm gate resistor. I would use a 47 ohm gate resistor to replace the originals and install new power supply fets. Be sure to replace the driver transistors as well marked 1A and 2A or 1G and 2G. There are 4 of them next to the PWM chip marked TL494C. I would also check the outputs likely some or one is shorted.

When you refer to "N" and "P" channels fets, those are outputs. The 501S used IRF540 and IRF9540 for the outputs.

Rockford only used IRFZ40's in some of the older DSM amps but did not use them for long. They used BUZ11, IRFZ40, MTP50N06V, MTP75N05HD and a couple others.

joesch1999 23rd December 2012 06:34 AM

Thanks sean so stay with the 3205's then just change the smr and drivers? Yeah there are blown p as well

seankane 23rd December 2012 07:56 AM

Stay with the IRF3205 and change the gate resistors (hooked to the gate leg of the IRF3205) to 47 ohm. The are smd 0805 pakage. Then change the 4 driver transistors as well.

If the supply has failed replace everything so it is reliable. The supply failed for one or more reasons, determine those as well. Either reverse polarity, or shorted output fets. If the output(s) test shorted remove them from the circuit before powering the amp or you will take out the supply again.

Perry Babin 23rd December 2012 02:33 PM

Using a small fuse (10 amp) or a current limiter in the B+ line AND having all transistors tightly clamped to the heatsink will greatly reduce the chances of damaging new components when applying power.

If you replace the output transistors, set the bias pot for the repaired channel to the fully counter-clockwise position before applying power.

joesch1999 23rd December 2012 02:55 PM

thanks perry & sean

joesch1999 1st January 2013 05:02 PM

ok drivers are 2az and 1m what are the part numbers to order these I have mmbtao6lt1 and mmbd914lt1g

seankane 1st January 2013 06:37 PM

You should use any of the following:

MMBT3904=1AM/1A=NPN
MMBT3906=2A=PNP

MMBTA56=2G=PNP
MMBTA06=1G=NPN


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