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Old 12th September 2012, 08:52 PM   #1
chipper is offline chipper  United States
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Default Rockford fosgate punch 40 repair help

Hi guys, I got here a punch 40 amp it needs repair for the power supply. When I got it it had blown power supply both fets looked like they blew up I removed them put in new irf3205s changed gate resistors applied power from my pyramid power supply and the amp put it into protect. One ps fet (q6) got super hot fast. I checked outputs 540 and 9540 on both channels they all measured out fine out of the circuit board. Not sure what's going on with it.

Also what's really weird is I can apply power to it with out the power supply mosfets and you can see the led glowing.

Just GND and B+ and the led will light lightly. Could it be a shorted driver transistors? I'm asking because I don't have access to a VOM and my metter only measures resistance no voltage.


Btw this is a Rockford Fosgate Punch 40.2 with the light grey heat sink
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Old 12th September 2012, 10:36 PM   #2
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*i can get access to VOM but my dad isn't home so I'll have to wait to measure any voltage. But can someone please explain why the led lights up lightly when I applie GND and REM??

There's NO power supply mosfets installed when it does that. This is the 1997 model punch 40.2. Thanks
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Old 13th September 2012, 05:15 AM   #3
chipper is offline chipper  United States
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Anyone? Anyone? I'm stuck on this, I took all the driver, ps fets all out and when I put gnd and rem the red led still turns on lightly. I also tried replacing the drivers and that did nothing except still burn up fets still. And when I put new drivers I check the gate voltage and it was measuring 7.89 dc on both pads. I really need some help on this one.

Could it be TL494C is defective?
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Old 13th September 2012, 07:20 AM   #4
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If you're using the gate voltage for troubleshooting, you must have the power supply driver transistors in place. Replace the driver transistors and measure the voltage again.

The 494 could be defective. If you're unsure, post the DC voltage for all of the pins.
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Old 13th September 2012, 08:24 AM   #5
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I put in new driver transistors and I still read 8.46vdc on the gate pads for both mosfets. Now on the 494c I had my negative probe on the GND and started measuring voltages on both sides.

Starting with one side

Pin 1= 8.51vdc
Pin 2= 10.57vdc
Pin 3= 11.59vdc
Pin 4= 11.76vdc
Pin 5= 9.69vdc
Pin 6= 10.32vdc
Pin 7= 8.98vdc
Pin 8= 12.82vdc

Then on the othe side of the IC

Pin 1= 8.87vdc
Pin 2= 11.77vdv
Pin 3= 11.79vdv
Pin 4= 11.78vdc
Pin 5= 12.82vdc
Pin 6= 12.81vdc
Pin 7= 12.83vdc
Pin 8= 10.48vdc

I started measuring where the stripe is on the IC all the way down. And why does the LED light up faintly even thought there is not fets in stalled??
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Old 13th September 2012, 08:28 AM   #6
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There is no ground. Use the pin numbering scheme in the attached photo and repost the voltages.
http://www.bcae1.com/temp/pstl594pinnumbers01.gif
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Old 14th September 2012, 03:48 AM   #7
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I measured pins across from each other (1 - 16, etc)

1-16 - 0.511vdc
2-15 - 1.166vdv
3-14 - 0.76.5 mV
4-13 - 0.003.3mV
5-12 - 3.450vdc
6-11 - 2.557vdc
7-10 - 04.23vdc
8-9 - 04.25vdc
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Old 14th September 2012, 06:42 AM   #8
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If you replaced the power supply fets and didnt change the drivers, you probably smoked a power supply fet. It was probably the one with the blown driver. Then when you replaced the driver the blown fet(s) smoked.

Replace all the power supply fets and drivers at one time all together. Re-check your gate resistors to make sure they are within tolerance and have a good connection to the pad and the 1st leg of the power supply fet. Confirm this by placing one probe on the gate leg of the fet and the other probe on the other side of the gate resistor.

Make sure to check D2 and D3 to see if they are shorted. Usually if they are they will fry fets upon hooking power and ground but I have seen it go both ways. If they are shorted remove them or take some off of a parts board and replace them.

Before powering check your outputs again. If there is any question in your mind just remove them, you can always put them back in.

The voltage regulators rarely fail, but check them. Also check the rectifiers. They rarely fail as well but I had a 250m2 I was repairing one time and kept blowing power supply fets because I had a shorted rectifier.

If the regulators and rectifiers test good go ahead and power up the amp but dont forget to turn the bias pots fully counter clockwise.
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Old 14th September 2012, 05:56 PM   #9
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I just got a 1996 punch 40x2 the boards are practically the same just the 40.2 doesn't have the psd connection. Can I just take the board out of the 40x2 and put it in the 40.2 heatsink? Reason why is because the punch 40.2 is brand new looking and complete with the gold end caps.

About the 40.2, I removed all the outputs even removed the rectifiers none of those actually changed the gate voltage from changing.

I replaced the drivers with new ones. And I get 8.56vDC on both gate.

But if I can't get this one to could I just use the 40x2 board in place of the 40.2 board?
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Old 15th September 2012, 03:50 AM   #10
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Yes they are identical boards they just left off the psd port but the board is plumbed for it. Thats how they got rid of their old stock boards. You can actually add the port and the resistors to the 40.2 board and make it a 40x2 thats the only difference.
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