Peavey CX4080HZ blown channel repair

[Delta362]

My apologies on misunderstanding your question. I'll have to check later today, but I believe they are 10000uF, 100V rated caps.

[Delta362]

Definitely 10000uF, 100V. While the board was removed from the amp, and the large heatsinks removed, I was comparing components for both channels. Q305 read odd in one of the directions compared to Q105. I pulled it out and tested it by itself and it was ok. The board pins read the odd readings. I then removed IC300 and the board pins that were reading different from Q105 were now reading the same. I've got a new MMPQ6700 on the way.

[x-pro]

This means that the power supply to the amplifier should approximately be in the range of 85-95V per arm.
This begs the question: why do you have 10V power on one arm?

[Delta362]

With the transformer unplugged, I read 120VAC for the inputs for the two HV rails (positive and negative feeds). Given that my LBL is still bright, there's something pulling lots of current and pulling these voltages way down. I have a new IC300 on the way. I have not powered it back up since removing that. I'm still looking at all the components between the channels to see if I can find any other discrepancies.

[Delta362]

Last night I pulled Q131, Q132, Q331 and Q332 and with the LBL, I powered the unit on with the 6 pin J1 transformer connector plugged in. IC300 is removed as I am awaiting the replacement to arrive. It took several seconds for the speaker output relays to click on, but that's something they only did when I had J1 disconnected previously during my troubleshooting. I then measured the HIRAIL and LORAIL voltages on the board on the empty MOSFET pads and got ±105VDC on the HIs and ±52VDC on the LOs. These look very reasonable.

So next step is to install the new IC300, remeasure. Then look at connecting installing Q131, Q132 and see if it holds up. Then look at installing Q331 and Q332.

[Delta362]

Victory! I first installed the new IC300. Powered up on the LBL and checked the high voltage rails. I had similar ±105VDC and ±53VDC. Next I installed Q131 and Q132 and powered on with the LBL. Same voltages. Then I removed the LBL and powered on. I now had ±160VDC and ±80VDC for the rails. No issues found and the right channel was working.

I then installed Q331 and Q332 and powered on with the LBL. Rails held up. I then removed the LBL and powered on without the LBL and both rails held again.

I had talked with Peavey on the issue as well. They suggested replacing a few other components that may be weak or leaky. In the end, I had replaced the following parts:
Small devices - Q302, Q309, Q310, Q333-Q336, IC300 (this was definitely leaky), IC305 and IC306.
Larger devices D309, Q331, Q332, and Q313-Q328.

A few of the small transistors may have been ok, but they were cheap and easy to replace while I had the board out.

Both channels of the amp are finally working. Thank you!

[x-pro]

It's so simple - change all the parts and everything will work. Without even delving into what and why.
And why is this forum needed when "heavy artillery" can be used?

[Delta362]

x-pro, changing all of those parts wasn't my intention. I don't like to shotgun parts as I want to learn and understand the circuit. However, the only parts that I changed that may not have needed it were the small transistors. They were cheap. This particular unit was a pain to disassemble/reassemble/test/repeat since the owner broke off all of the board mounting tabs and installed screws from the rear instead.

[DrGonz78]

x-pro, changing all of those parts wasn't my intention. I don't like to shotgun parts as I want to learn and understand the circuit. However, the only parts that I changed that may not have needed it were the small transistors. They were cheap. This particular unit was a pain to disassemble/reassemble/test/repeat since the owner broke off all of the board mounting tabs and installed screws from the rear instead.

I remember Enzo saying the same thing. Like if he had a board out and would replace a suspect transistor or something. 10 cents for a piece of mind. It’s a bit different thinking than just throwing parts at something. There is always this fine line trying to not shotgun anything.

[g1]

Sometimes this method is the factory recommended method. It doesn't help us understand the failure, but is the most economical solution.
Remember this x-pro ?

[x-pro]

These watches are for clients

[x-pro]

and where is your professional approach?

[Helmholtz]

C'mon, not fair to bash x-pro for his post.
Was just expressing his personal frustration. I can understand that and have some sympathy.
He was the only one giving valuable advice here and I'm sure it would have led to success

Of course, no reason the criticize the OP's course of action.

[x-pro]

Thank you.
I'm not offended.
Even if I suddenly get banned.
Life goes on, there is still a lot of exciting things to do.

[Delta362]

x-pro, if I wasn't clear earlier, I greatly appreciated your help with this as well as with my other amp adventures!