Yamaha CR-800 Receiver Bias on R channel

[ChancesR]

Good afternoon. I've been reworking this receiver - I have replaced the output transistors, and the relay. I am able to set the Idle current on both channels without issue - but when trying to set the voltage to "0", the right channel fluctuates and will not hold any value. Jumps off the charts in both directions. Left channel is stable. I have the service manual, and have checked all components in circuit. I'm not finding any obvious problems. I would like to know what/where to look next here.

I'm checking this without a load. Relay will go off/on, protection mode. I'm really hoping someone has an idea.

Regards!

[Jazz P Bass]

Try swapping out the two resistors at the input to the power stage.
The Long Tailed Pair.
I do not have the schematic.

[ChancesR]

Thank you! Would you be talking about the 2 100ohm 1/4W FP resistors that stand up high? Although they check good in-circuit, I'll change them and see.

Again, Thank you!

[Jazz P Bass]

Sorry, my bad!
What I had every intention of typing was "Transistors"
The LTP transistors are tied together at one leg.
TR602 & TR603
The input signal goes to the base of one & the return feedback from the output goes to the base of the other.
Link to schematic:http://www.stereo411.com/forum/viewtopic.php?f=2&t=3507

[ChancesR]

Hi Jazz
Thank you - that makes so much more sense. ha I'll pull those today and check out of circuit. I'll post back!

Again, thank you for your time
Regards

[Jazz P Bass]

I would just replace them.

[ChancesR]

Hi Jazz,
I realized that the schematic you have been referring to is for the CA-800. What I'm working on is the CR-800. ANYway....I believe you are correct in the driver replacement.

Schematic shows 2SC1124/2SA7063 as the drivers - obviously obsolete. Would you or anyone know of a source for these?

I researched as best I could - and the best sub I came across would be 2N6126/2N6123. Can someone verify that? The original (2SC1124) specs show 140V, 1A, 950mW, 120mHz, hFE 160 at 1C, 100mA. This 2N6126 is an 80V, 4A, 40W.......but appears to be the most compatible.

Thanks all - !

Regards

[Jazz P Bass]

Uhmm.
Who said anything about replacing the drivers?
I thought the problem was you could not get the DC offset to settle down.
That would be the LTP transistors at the beginning of the circuit.
TR 701-703 one channel
TR 702-704 the other channel.
Yamaha calls this the midpoint voltage
Go across TP3 (+) & TP5 (-) and adjust VR701 for 0 Vdc
Go across TP4 (+) & TP6 (-) and adjust VR702 for 0 Vdc.

[oc disorder]

There's a possibility it could be a faulty trim pot..

[ChancesR]

Just wanted to say "THANK YOU" for the help here. I ordered the replacement transistors (2SA763) and was able to have stability on the Bias adjustment. It's sounding GOOD. I have some minor things to do yet to fully complete this - cleaning all the pots - but it's a good day. ha

Again, Thank you.

Regards and good fixin's to all.

[Jazz P Bass]

Glad to hear that you have it repaired.