Punch 500a2 distorted channel

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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:
 
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.
 
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?
 
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.
 
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! :((
 
Check all of them. Check from gate to drain. Cut the ones that read 0 ohms free from the board (all 3 legs) and re-check to see if any others read 0 ohms. When re-checking, also check for shorts from drain to source.

Q7 reads from drain to gate .7 ohms and from drain to source i get 241 ohms
Q11 reads drain to gate .2 ohms & drain to source it reads 526 ohms
Q6 completely shredded itself
Q10 reads from drain to gate .7 ohms & drain to source it reads .3 ohms.

And yes i pulled the fets out of the board. Does this mean its going to survive?
 
Those have all failed.

If you're going to use the 3205s, and need the 47 ohm resistors, you can get them at mouser or digikey. They're 0805 (size).

Do you have any power supply FETs that you can install to allow you to continue troubleshooting?

I have a couple savaged MTP75N's in my tool box in a plastic bag. Could i use two fets to see if it will start on?
 
Yes but you need to remove all defective outputs (check gate to drain).

Check the gate resistors after removing the FETs to confirm that they're within tolerance.

Install them and measure the gate voltage. Make sure that both sides have ~5v DC on the gates. If the voltage is not the same from one side to the other, there may be a problem with the drive circuit.

When measuring the voltage on the gates, do so with ONLY remote and ground connected. Do NOT connect the B+.
 
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