Reduced output from Marantz 1060


2014-04-19 11:33 pm
I'm having problem finding the cause of a reduced output from a Marantz 1060.

History, recapped, great result, worked for a month, then distortion and reduced output from left channel, changed transistors (and diodes on the power amp board. Bit of smoke from that board on a rushed start up with a couple of output transistors out of the left hand side, I'm presuming a short, I think the smoke was from a trim pot on one channel (right), replaced.

There is no visible damage on the board. Distortion is cured!

However still a reduction from from the left channel, maybe 90%, but also now right channel 50%.

If I take a pre out it sounds fine.

The DC and bias set just fine, outputs are original but test spot on. I have checked and rechecked parts, mainly in circuit, I've checked solder and conductivity. Recent parts replaced (all caps changed previously)

H701-H702 KSC945C
H703-H704: 2N3440
H705-H708: IN4148
H709-H712: 2N5416, 2N3440
H713-H714 1N4448

I need to dig deeper and remove more parts and test out of circuit - but I hoped someone might be able to point me in a likely direction. I don't have an oscilloscope, yet.