RF punch 800a2 channel repair question

Hi forum, I recently bought a punch 800a2 not sure of the board rev # still waiting for it to come. Anyway I wanted to know is it hard to repair the channels on these? This one has one blown channel (according to the seller) I've never repaired one of the larger RF amps before.

What components in the shorted channel would need to replaced in order to get it working?
 

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When you get it re-post and I will help you. No sense in writing up long post about what "could" be wrong.

Likely it has shorted outputs, as well as some defective source resistors.

You will need to replace all the outputs and source resistors in the channel.

You will also need to check/replace any gate resistors for the output FETS.

If any of the source resistors are open you will likely have protection circuit issues to deal with.

You will have to check the various 1A and 2A transistors, and the 5D and A7 diodes for leaks or shorts.

There is also some 20 ohm resistors that usually need replaced in the channel as well.

Call Rockford get the schematic and re-post when you get it.
 
When you get it re-post and I will help you. No sense in writing up long post about what "could" be wrong.

Likely it has shorted outputs, as well as some defective source resistors.

You will need to replace all the outputs and source resistors in the channel.

You will also need to check/replace any gate resistors for the output FETS.

If any of the source resistors are open you will likely have protection circuit issues to deal with.

You will have to check the various 1A and 2A transistors, and the 5D and A7 diodes for leaks or shorts.

There is also some 20 ohm resistors that usually need replaced in the channel as well.

Call Rockford get the schematic and re-post when you get it.


I need some help. Q8, Q7, Q6, Q5 run a little above warm when idling while the other side stays cool. What's causing this? Thanks
 
I need some help. Q8, Q7, Q6, Q5 run a little above warm when idling while the other side stays cool. What's causing this? Thanks

Well if one whole channel was shorted then obviously you clipped the legs of the FETS to enable the amp to power and idle.

The side of the power supply that is still driving the enabled FETS will get warmer more quickly than the side that has the FETS clipped, especially if the board is not mounted in the sink.

It should take a little bit for them to get warm though. They should not be getting warm very quickly if the amp is just idling.
 
Well if one whole channel was shorted then obviously you clipped the legs of the FETS to enable the amp to power and idle.

The side of the power supply that is still driving the enabled FETS will get warmer more quickly than the side that has the FETS clipped, especially if the board is not mounted in the sink.

It should take a little bit for them to get warm though. They should not be getting warm very quickly if the amp is just idling.

Yes I desoldered them from the board and all of the open source resistors (all of them were no good) didn't take out anything else. I also wiggled the transformer around didn't seem to do anything. One bank of fets get really warm when mounted tightly to the sink while the other side just chills. It's not making any sense to me. Both bias pots are turned down.

Weirdest thing is they start to heat up after a minute of being powered up. Could it possibly be the channel that failed? I also noticed a group of smd components get very hot on the failed channel.
 
Do you have DC on the output terminals of the defective channel?

Do any of the power supply FETS from the defective side test leaky or shorted?

Are any of the gate resistors for the power supply FETS in the defective channel shorted or out of tolerance?

Have you checked the drivers for the power supply?

Is the amp making rail voltage?

Is the amp making regulated voltage?

Do you have any solder bridges on the pads of the removed FETS in the defective channel?
 
I think maybe you should get those source resistors back in as well as the output FETS.

Then check the protection circuits and make sure you don't have any shorted transistors or diodes.

You will have to check the gate resistors and various smd resistors to make sure none are shorted or out of tolerance.

You need to repair the output section first.
 
I think maybe you should get those source resistors back in as well as the output FETS.

Then check the protection circuits and make sure you don't have any shorted transistors or diodes.

You will have to check the gate resistors and various smd resistors to make sure none are shorted or out of tolerance.

You need to repair the output section first.


So there's a chance there may not be anything wrong with that bank of power supply fets? When I used the batts from out tv remote, I checked the gate voltage and got a steady 5.36vdc on each fet and checked the voltage going into the amp and it was at 13 voltages.

I also noticed the power supply has mixed mosfets 4 mtp75n05hd and 4 irf3205. Just thought I'd throw that out there.
 
This amp does not have separate power supplies. The power supply FETS all need to match.

Since its been repaired, I think it would be a good idea to go through the power supply completely for the amp to be reliable.


I really have to now I popped a 75n05hd by accident when I was probing around in the power supply. Amp was still on after that happened! Like a piece of the mosfet just blew off and scared me sh#tless! I'm going to replace the whole thing and see if that eliminates the one bank of fets heating problem. And move on to the channel.
 
I agree with Sean, the power supply FETs need to match & need to go through the power supply thoroughly for reliability. You need to do that now anyway, check the drivers & gate resistors thoroughly, as maybe that was overlooked during a previous repair causing the uneven heating of one bank.

If you have to order parts, make sure you order gate resistors & driver transistors as there cheap, if you don't already have extra.

Main reason for me posting here is to say be careful when you got the back off testing stuff, FETs can blow apart & throw pieces of themselves violently, could really mess up an eye. I had some close calls over the years & highly recommend wearing safety glasses when the backs off & the amp has problems.