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Cliff, my man, you were so helpful regarding my shorts, I've got another one for you. In the same channel, when I try to set the DC offset, the reading won't stabilize at 0 volts, but fluctuates +/- 2 volts or so. In addition, instead of 8mV for the idle current, I get 0 mV. I've checked the output transistors and the resistors and all seems to be well. The capacitors are all new. The left channel reads fine on both counts. Any ideas?
I suppose not or you would not be asking!
But this is the ideal instrument to tell whether the amp is oscillating or not.
Otherwise difficult to tell. If there is zero bias in the O/P transistors it is likely that the offset will flip between two values since it is unstable in the zero bias condition.
Can you check voltages across the biasing diodes, or transistor/pot?
The only scope I have is in a mouthwash bottle. Here's a link to the Marantz schematic. I don't know if you have to register to view it. The P-700 board is the main amp.
My first vacation job, some 50(ouch!) years ago was drawing stuff like that! Pen, ink and stencils ...
Anyway, where are you measuring the Iq? Can't see any test points! Across one of the 0.2R emitter resistors? With what? A standard 3.5dig VOM?
Really nice kit, Marantz. I feel a nostalgia attack coming on!
Schematic designation for emitter resistors?
Here's another clue as to the possible probable. Resistor # R-727 looks like it was burned out and replaced. Anything in line with that which could be affected too?
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