punch 200.**

[ian33]

I am working on a punch 200 amp (25/4-4ohms)This amp will not power up.I replace 4 burnt ps fet (irfz44) D3 (1N4003 shorted)It also had two shorted sm transistor (p2gb)I install two a733 in there just for test.I have 14.2v on all the center leg of the ps fets.On the first leg i have 1.5v and the third has .0v.I used a 1n4001 in place of the 1n4003

LM339D
pin 1: .1vdc
pin 2: 6.3v
pin 3: 14.5v
pin 4: .2v
pin 5: 2.5v
pin 6: .0v
pin 7: 14.5
pin 8: 4.7v
pin 9: 4.8v
pin10: 4.8v
pin11: 8.9v
pin12: .ov
pin13: 6.3v
pin14: 6.3v

TL494 ic
pin 1: .0vdc
pin 2: 4.5v
pin 3: .0v
pin 4: .1v
pin 5: 1.5
pin 6: 3.3v
pin 7: .ov
pin 8: 14.1v
pin 9: 3.4v
pin10: 3.4v
pin11: 14.1v
pin12: 14.1v
pin13: 4.8v
pin14: 4.8v
pin15: 4.8v
pin16: .0v


any idea what could be the problem?

[Perry Babin]

Are the gate resistors within tolerance?

Did you check the NPN driver transistors to confirm that they were not open/damaged?

Do you have a scope?

[ian33]

The NPN transistor had a good reading on board.some of the gate resistors is install upside down.Am guessing all of them should be the same at 1o ohms?I dont have a scope.

[Perry Babin]

What's the PC-# on the circuit board?

[ian33]

pc 3084

[Perry Babin]

I don't have the schematic diagram for that amp but the 800.4 (PC-3085) used 10 ohm gate resistors so it's possible that that's what this amp should have.

What's the DC voltage on the base, collector and emitter of the NPN driver transistors?

[ian33]

i found two bad gate resistors but still no change


npn sm transistor 1

base 5.6v
collector 14.5v
emitter 1.8

transistor 2
base 5.6v
collector 14.4v
emitter 1.7v

[Perry Babin]

Those appear to be defective also. With 5.6v on the base, I'd expect something closer to 5v on the emitter.

[seankane]

Perry I have a board sitting here that is a 500x 4 channel like the one you helped me with and it is a PC 3084. Irfz44 never came in these stock. They used irf3205 and I have seen them with MTP50N06V. Not saying they wont work just never seen those in one of those amps.

[seankane]

I would consider starting over and rebuilding the power supply. I would install 4 new p/s fets, 4 new gate drivers, and 4 new driver transistors.

I would also check the transformer for broken legs as the one I just repaired had 2 broken legs. Chances are if you have defective gate drivers you have p/s fets that are defective as well.

Make sure you dont have any shorted output fets or when you do get this amp up and running you could have another p/s failure.