Yamaha CR-620 transistor overheating

[saharajim]

Hello all. I'm looking for some help with my CR-620 again. I repaired this receiver a couple of years ago and now it's needing some more work. A couple years back I replace TR722 a 2SB560 as I found it was shorted C to E. With help from AKer's. http://audiokarma.org/forums/index.php?threads/yamaha-cr620-repair-question.648377/
Well this time it blew the main 3 amp power supply fuse and TR722 has failed again and this time the outputs failed as well TR724 and TR726. I've replaced all three installed a new fuse and slowly powered it up using my variac and watching the current. The issue is it seams to power up fine and both channels are working however, even at very low output TR722 gets too hot to touch and I can smell it or something burning. I've checked over the rest of the transistors and they seam to be fine. Any suggestions on why this transistor is so hot and what to check is appreciated.

 

[saharajim]

Also I used new MJ21193G and MJ21194G for the outputs.

 

[avionic]

Did you readjust the idle current( bias ) after replacing the outputs.

 

[avionic]

Also did you check that the emitter resistors are still serviceable ?

 

[saharajim]

Yes, I adjusted the idle current and seams to be good at about 8mv. I didn't check resistors but I'll do that tomorrow. Are you talking about the ones on the outputs or all of them? Should I pull them or check in place? avionic thanks again for your help.

 

[llwhtt]

How about C730 across the base/collector of TR722?

Craig

 

[saharajim]

I checked the resistors in the emitter of 722 and 726 and they are all ok. What I did find is what appeared to be a very poor solder joint on the collector of 726 so I touched it up. Do you guys think this could have anything to do with my issue? I powered it up again and did some voltage measurements and they look ok to me. Similar to those on the schematic. Craig I'll check C730 too. However the weird thing is that today after I checked the resistors and touched up the solder joint I played it for about a half hour and it didn't heat up this time.

 

[avionic]

very poor solder joint on the collector of 726 so I touched it up

That could very well have been the problem.