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-   -   Punch 500a2 distorted channel (http://www.diyaudio.com/forums/car-audio/180975-punch-500a2-distorted-channel.html)

chipper 12th January 2011 02:56 AM

Punch 500a2 distorted channel
 
I got a Rockford Fosgate punch 500a2 for $25 it is in near mint condition one channel works great but the other is distorted i thought it was a open source resistor which one looks burnt and three IRF9540's read 0 ohms from gate to drain, source. And two gate resistors read 8 ohms instead of 10 or 11 ohms (norm?). Wondering if i can replace the bad source resistors and and gate resistors and bad three 9540s? Can i leave the original IRF540s in? Since those read normal.:confused:

chipper 12th January 2011 03:29 AM

And i have a punch 225.2 sitting here with a shot power supply but i checked the output mosfets and theres some good reading IRF9540's sitting in there, wondering if i can use those? and some source resistors? Or would that be a bad idea???

Perry Babin 12th January 2011 11:32 AM

If this is your own personal amp, you can use used parts to repair it. If it's for a paying customer or for sale, you should use new parts. The replacement parts are going to cost less than $10.

If the gate resistors are not within 5% of the marked value, they should be replaced. If one of the source resistors opened or is well out of tolerance, you'll need to check the protection circuit resistors connected to that resistor.

chipper 12th January 2011 01:49 PM

Quote:

Originally Posted by Perry Babin (Post 2430401)
If this is your own personal amp, you can use used parts to repair it. If it's for a paying customer or for sale, you should use new parts. The replacement parts are going to cost less than $10.

If the gate resistors are not within 5% of the marked value, they should be replaced. If one of the source resistors opened or is well out of tolerance, you'll need to check the protection circuit resistors connected to that resistor.

Yes this is my person own am that I'm keeping for my collection 15 other amp hehehe.

Yeah, I looked inside because it sounded distorted and one resistor looks like it heated up pretty good. I have new IRF9540's that I got awhile ago from vishay. I want to know if i can leave the original IRF540's there?

Dr Zeus 12th January 2011 02:30 PM

I'd remove all the IRF9540s in the bad channel and then put just one new, good 9540 in and replace it's source resistor as well. If the amp is stable with power and plays without the distortion and minimal load through a test speaker then go ahead and put all the new IRF9540s and source resistors in.

For me, its kind of tough to test a slightly out of tollerance 0.10 ohm resistor with my meter so I just replace them. Ive seen a few RF amps where these resistors failed when the outputs fail.

stoke 12th January 2011 04:24 PM

i had one amp with almost the same problem but after replaced all the bad transistor, pulldown resistor and gate driver transistor i still get the audio distorted. the opamp look fine, what other things i have to check?

Perry Babin 12th January 2011 04:45 PM

chipper:
I'd recommend replacing all of the outputs in the blown channel but since it's your amp, it's your call.

stoke:
start a new thread if you need help. It's too confusing having two active repairs on one thread.

chipper 12th January 2011 07:27 PM

EDIT: I changed the resistors (.1 ohm) and powered up the amp for a minute with bad parts still in and it fried its self down good!! I'm really mad at myself for doing such s stupid thing!!! It blew the MTP75N05HDs and now the gate resistors are reading 40 ohms. I tested the drive circuit and its producing a signal of 4.7 volts. WHAT SHOULD I DO?!?!? I broke a good amp by a dumb mistake!

Okay if i replace the gate resistors, ps fets will it live to power on again?? I need help! :((

Perry Babin 12th January 2011 07:29 PM

What \'bad\' parts did you leave in it?

chipper 12th January 2011 07:30 PM

irf9540\'s and i think the irf540\'s also went bad. I just want to get it to work again!


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