Marantz SR-6000 -- fire in the hole!

[Duffalora]

Picked up a late '70s Marantz SR-6000 receiver (sorry, no pics before disassembly) in superb condition but not working. Turned in on using the DBT -- the bulb dimmed and it clicked out of protection. Took it off the DBT and turned it on in order to start troubleshooting. Bad move. Within seconds there was a popping sound from the voltage amp board (page 14 of manual) and then a flame out. RN23, a 330 ohm resistor, turned into a heap of molten slag, took out the neighboring diode and blackened the board. The transistor QN07 caught fire and cracked like an egg. Cool stuff! (see pics 1 & 2).

I pulled it apart, removed all the burnt bits (pic 3), cleaned the board (pic 4), tested neighboring parts out of circuit, and have since rebuilt it. One thing I did notice was the DC offset pot -- RN09 -- on that side was set to maximum when the flameout happened.

Because of my limited knowledge, a couple of questions before I put it all back together and try again:

1) Could the maxed-out offset pot cause the fire or should I be looking elsewhere?
2) I want to check out the power supply board before reassembly. Can I turn the receiver on and get accurate voltages on that board without connecting the other boards? (given the modular nature of most Marantz gear)
3) What's the chances that the STK modules have been taken out?

Thanks.

 

[Baron K Rool]

Those are Panasonic FC capacitors. Someone's worked on this, or was that you? Could be butchered. I would assume dead STKs, but that's just paranoid little me.

 

[bktheking]

Something pulled a shitload of current through that circuit, shorted stk or a backward diode, shorted diode.

 

[petehall347]

was the board wired up correctly ?

 

[Duffalora]

Thanks for the responses. Yes, there has been some recapping done -- I've checked it all and it looks OK. Board was wired up correctly. But I've just checked out the power supply board and have found some voltages that don't correspond to the service manual, chiefly the voltage at the main caps. Are these numbers a worry (please see attached table), in that they could cause problems on the other board? The main caps are original. Maybe rectifier diodes?

 

[Marcio Guth]

Hi, Marcio from Brazil. I have a sr-6000 with the same problem. Could some one help us? Tks

 

[pdm4606]

Sort of what happened to my Yamaha M-50 several years ago. Melted half the board and lots of damage. The board is located in the power section.
I salvaged half of the board and made a new other half board with a hand grinder and lots of care. Been working fine since. Making a new board was easier than I expected. Hand grinder used to make new traces then a small drill for holes. Fortunately traces were very big so it was easy. New cap. and resistors ordered from bay and it all worked. Of course a dim bulb was used at first try.