Fosgate 501s help please

joesch1999 · 05:39 AM

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 · 05:31 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

23rd December 2012, 05:36 AM	#1
joesch1999 diyAudio Member Join Date: Jan 2011	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 Last edited by joesch1999; 23rd December 2012 at 05:39 AM.

23rd December 2012, 05:54 AM	#2
seankane diyAudio Member Join Date: May 2010 Location: Washington State	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. __________________ Pyramid 52 Amp Power Supply----Fluke 787 Processmeter----Tektronix 465 Scope----Velleman HPS40 Scope----Soldering Iron----Desoldering Iron----Hejet HJ 500-S Heatgun----DM4070 Digital LCR Meter----Propane Torch

23rd December 2012, 07:56 AM	#4
seankane diyAudio Member Join Date: May 2010 Location: Washington State	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. __________________ Pyramid 52 Amp Power Supply----Fluke 787 Processmeter----Tektronix 465 Scope----Velleman HPS40 Scope----Soldering Iron----Desoldering Iron----Hejet HJ 500-S Heatgun----DM4070 Digital LCR Meter----Propane Torch

23rd December 2012, 02:33 PM	#5
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	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. __________________ Links >> Basic Car Audio Amp Repair * Basic Car Audio Electronics * New Site * Basic Switching Power Supply Design * Basic Computer Skills << Links

1st January 2013, 05:02 PM	#7
joesch1999 diyAudio Member Join Date: Jan 2011	ok drivers are 2az and 1m what are the part numbers to order these I have mmbtao6lt1 and mmbd914lt1g Last edited by joesch1999; 1st January 2013 at 05:31 PM.


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23rd December 2012, 06:34 AM	#3
joesch1999 diyAudio Member Join Date: Jan 2011	Thanks sean so stay with the 3205's then just change the smr and drivers? Yeah there are blown p as well

23rd December 2012, 02:55 PM	#6
joesch1999 diyAudio Member Join Date: Jan 2011	thanks perry & sean

1st January 2013, 06:37 PM	#8
seankane diyAudio Member Join Date: May 2010 Location: Washington State	You should use any of the following: MMBT3904=1AM/1A=NPN MMBT3906=2A=PNP MMBTA56=2G=PNP MMBTA06=1G=NPN __________________ Pyramid 52 Amp Power Supply----Fluke 787 Processmeter----Tektronix 465 Scope----Velleman HPS40 Scope----Soldering Iron----Desoldering Iron----Hejet HJ 500-S Heatgun----DM4070 Digital LCR Meter----Propane Torch

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