Power Plant P600

My P600 died about a month ago and I finally got her back up and running. I had to replace two caps on the main power supply PCB and a diode bridge rectifier on one of the DC supply/output amplifier modules. Post repairs she is operating and running great with everything measuring as expected with regards to the outputs of the transformer and the balanced output voltages to the receptacles. However, when I switch my meter to DC and measure from GND to either output leg to the receptacles I am reading 105 volts DC. If I measure across the output of the receptacles I am getting virtually zero DC volts.

As I understand, the 105VDC is the output of the bridge rectifier for each output module DC supply and my question is should there be any DC potential when measuring from GND to either output leg/receptacle? (If possible I would like to get someone with a P600 to measure their unit to see if what I am reading is normal or not)

Thanks in advance,

Nola man

That is not normal or safe. We suspect a Kapton short. Kapton is the insulating material we use between the transistors and the heat sinks.

Hi Paul, with some additional measurements to each output module, the problem has been identified and you are correct. The Kapton insulation tape on Q20 has a hole in it. Looks like it arced through. Not sure if this happened when the unit failed but it’s not on the output module that I replaced the diode bridge rectifier on.

Patiently waiting on the procurement of Kapton tape to get her back up and running in a safe yet high performance manner :)


Nola man

You are a great and skilled technician!

Hi Paul, do you guys still carry the main power supply PCB? The one that sits on the bottom panel and carries the oscillator PCB?

I replaced the Kapton tape on the DC power supply module that was shorting. The DC is no longer there but now I have ~64VAC on one side of the outlet and ~15VAC on the other and they both slowly oscillate. I pulled both modules and replaced all 12 3300uf 100v capacitors and reapplied the Kapton tape. I also replaced the other DC module bridge rectifier. With further measurements, it looks like one side is being pulled down as I no longer have the dual 80VAC going to each DC module. I have 91VAC and 56VAC, same on the main PCB. In addition I don’t have the dual 25VAC going to the main PCB but have 25VAC and 10VAC. I’m fairly certain that D1 on the main PCB is the culprit at this point.

Also, would you happen to know the value of R9 on the main PCB?

Thanks in advance,


We no longer have any of the PCBs left, sorry. If you want to give Alex a shout on Monday he can send you a schematic.

I figured it was a long shot that parts would be stocked for the original Power Plant series this far down the road but I understand

and I was just going to request a P600 schematic! Thanks again Paul.

A big thanks to Alex for sending me all the P600 schematics and service manual which really helped in troubleshooting!

She is back up and running with no faults and all sinewave/multiwave functions work as they should however, I’m still getting

the slow voltage fluctuations on both sides of the output/outlets with one side being 40 VAC lower than the other.

Scratching my head on this one. Any ideas?

Thanks again,


OK, found a bad GND trace on the main Hub PCB, fixed and the output voltages are now stable/solid but one side is outputting 59.96VAC and the other is 19.98VAC and again with no faults being displayed.

So close…