Yamaha CA-800 bias and dc adjustments.

[David Farber]

I have a Yamaha CA-800 in for service. I repaired a noisy channel by
replacing TR601 on the power amplifier board. I'd like to be able to adjust
the bias and dc offset but since this amp has class A capabilities, there
are four adjustments per channel. I'd rather not guess here. Anyone have
some knowledge about this?

Thanks for your reply.

 

[Mark D. Zacharias]

I have a Yamaha CA-800 in for service. I repaired a noisy channel by
replacing TR601 on the power amplifier board. I'd like to be able to
adjust the bias and dc offset but since this amp has class A
capabilities, there are four adjustments per channel. I'd rather not
guess here. Anyone have some knowledge about this?

Thanks for your reply.

1. They say to turn OF the Pre/main coupler.
Personally I'd just turn the volume control down...
2. No speaker load.

For Class B:
3. Set voltage between TP 1 and TP2 to - (UH-OH. POSSIBLE MISPRINT ALERT!)
Manual says 15 VOLTS, using VR 602.
4. Set DC offset using VR601
5. Set DC between TP 3(+) and TP4(-) to .047 volts using VR 603.

Class A:
6. Set voltage between TP 3(+) and TP4(-) to 0.8 volts using VR604
7. Repeat procedures until each is within limits.


Mark Z.

 

[David Farber]

1. They say to turn OF the Pre/main coupler.
Personally I'd just turn the volume control down...
2. No speaker load.

For Class B:
3. Set voltage between TP 1 and TP2 to - (UH-OH. POSSIBLE MISPRINT ALERT!)
Manual says 15 VOLTS, using VR 602.
4. Set DC offset using VR601
5. Set DC between TP 3(+) and TP4(-) to .047 volts using VR 603.

Class A:
6. Set voltage between TP 3(+) and TP4(-) to 0.8 volts using VR604
7. Repeat procedures until each is within limits.


Mark Z.

Thanks for the numbers Mark. That 15 volt measurement is correct. It's even
marked 15 volts on the pc board. (-; It just doesn't indicate how to adjust
it.

Now that I repaired the popping channel, I noticed a much lower level noise
going on in the preamp section. Any chance you have a schematic that can be
easily sent electronically?

Thanks for your reply.