PMP5000 information
Yes, the main power supply will run without the power amps connected HOWEVER there are NO bleeder resistors and the caps store a massive charge at 80 volts, and one needs to bleed the charge before connecting the amp!!!
There is so much current initially that fusing the soft start resistors is probably futile.
I just got my second PMP5000 restored and back together today. Here is the diagnosis and the work accomplished:
The rear power amp had an insulation breakdown from the drains of the three switching transistors to the source of the 9640 transistors. (These are in parallel as complement to the single other side switcher transistor)
The circuit board was bubbled and the cancer was ground out with a dremel tool. Clear epoxy was put over the area. The drains of the 9640's were drilled out and the replacement transistor drains were left full length and sleeved.
Since the grinding removed the source tie trace between the 9640's, this was hardwired with hookup wire.
Since the grinding removed ALL the drain connections of the 3 switching transistors, these were hardwired between them. A hardwire connection was also made to the drain of the single transistor to connect it to the toroid inductor lead closest to it.
Next, the 30 milliohm metering resistor on the bottom side was replaced as it had disintegrated.
An 18 volt, 500mw Zener diode (surface mount) was replaced that was shorted. This is part of the gate drive to one of the 9640's.
The amp was powered first at low voltage from current limited supply. It did not work, but since it did not smoke, it was connected to the main supply after bleeding the caps. One can turn the panel at 90 degrees and have the cables from the panel connected to the amps and supply by putting a book or spacer between the supply and the back of the panel. It still did not work.
Surface mounted transistors T12 and T16 were found to be shorted when the 30 mohm resistor opened. These transistors detect excess current in either polarity through the 30 mohm resistor and their collectors "OR" the signal into a latch of cross coupled transistors, which shuts down the drive signal to the switchers in the amp. (there are seperate ones for each side amp)
These two surface mounted transistors were replaced and the dead side of the amp came alive!
My first amp had the power supply destruction to repair and the same failed amp circuit board fireworks. In this second one, the 30 mohm resistor fused and saved the power supply.
In the my first PMP5000, the softstart resistors got cooked because I tried to start the supply before all the baddies were out. The main switching transistors were gone, the drivers of those were gone, the diodes at the gate drive were gone, several small components were gone, and the 8 lead switching control chip for the main supply was gone.
To sum it up, the failure in the rear power amp can do damage to itself and the main power supply when it arcs out. On the first unit I repaired, the 30 mohm resistor did not open and there was NOT much evidence of the arc and short in the rear power amp, but the smoking gun was there right next to the heatsink. It can easily be missed if there was little flame there and one will immediately blow up the freshly repaired power supply if one connects it again without repairing the amp section.
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