Yamaha CR-600 Offset Issue

ivandezande

AK Subscriber
Subscriber
I think I'm cursed from working on CR's, second one with strange issues. This guy had a blown bridge rectifier and everything else seemed to be fine.

On the driver board I replaced the caps, the bias transistors Q707,8, Q705,6 as they were Sony's that I've had problem with, and trimmers.

It biases perfectly, but when I measure for offset between test points, it looks to be almost negative 30V on each output! I checked for transistor installation, but 7 and 8 are fine if the SM is right and it biases so not worried about 5,6 and they are supposedly in correctly.

I'm seeing -37V on the collectors of 707,8 which should be -1V. Emitters are -27V and -37 respectively. Bases are correct at 37V.
On the input pair, I'm seeing 37V on both collectors which isn't right.
 
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1 & 3 / 2 & 4 are bias TP's.
3 & 5 / 4 & 6 are offset TP's
 
So your seeing damn near rail on both channels at the outputs?
 
What voltages are you seeing around TR707 and 708?
I'm seeing -37V on the collectors of 707,8 which should be -1V. Emitters are -27V and -37 respectively. Bases are correct at 37V.
On the input pair, I'm seeing 37V on both collectors which isn't right.
 
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