Yamaha CR-220 Sound issues

[Peter S]

Hi Keneye and avionic;
I have a CR-220 that had both output transistors shorted on the left channel. Both were replaced, one driver transistor was split in half, this was replaced. The other driver was tested OK in circuit. All transistors and diodes for the left channel test OK in circuit, but the left channel still slowly (take about 5 seconds) swings to - 22 volts.
I removed both outputs for the left channel and output still slowly swings to B-. (with no speaker connected) . The right chan plays fine, tuner section is working normally. Could this just be a leaky cap somewhere in L chan amplifier section?

 

[mbz]

I have a CR-220 that had both output transistors shorted on the left channel.

What caused the outputs/driver to short? Someone fiddling with spkr cables causing short?
Check R747, 749(4.7ohms) and emitter resistors R751, 753(0.33ohms) for signs of stress.
Either something is failing open or short. With one driver "split" the other can't be too far behind, in circuit diode
test can be misleading... If TR717 is original then consider replacing.

 

[Peter S]

Hi mbz, and thanks. I have removed the outputs and still get the same slow swing to negative. I have replaced every electrolytic in the left chan except the small bi polar's

 

[Peter S]

Can I also temporarily remove the drivers ( TR715, TR717 ) and power up without damage?----Well I removed the drivers also, and the output STILL slowly goes negative (probably all the way to B-)

 

[mbz]

Measure dc voltages at TR715, 717 base to ground, measure at the solder eyelets since you've removed the TR's.
Not much time today, others may chime in...