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[Guest]

I need a schematic for a Yamaha R-900 Receiver.

The protective circuit relay has stopped engaging.
Any advice or assistance is appreciated.

Thanks,

Mark

[Tim Schwartz]

Mark,

Unfortunately, I don't have a scan of this schematic. What the failure
most likely means is that the protection circuit IS working, and you
have a bad amplifier channel. Look for DC voltage on the emitters of
the output transistors. One channel will probably be near 0, and the
other will have quite a bit of + or - DC on it., which is what the relay
is there for. It is less likely though possible that the protection
circuit itself has developed a fault.

Regards,
Tim Schwartz
Bristol Electronics

[Guest]

Hi Tim,

Thank you for your reply.

I have not had a chance to check the Yamaha, however I do have a
Marantz 2330B that has DC Voltage in one channel.
So, from a novice, what would dc voltage indicate?

Thanks,

Mark

[Mark D. Zacharias]

(Butting in....)

If it's the full rail voltage, could be a bad transistor, preamp transistor
pair, bad resistor, bad cap.

Intermediate voltage I'd lean more to a bad cap (feedback circuit)

Mark Z.

[e279rle]

I had a similar problem a few yrs back w/ my 795a, and it has just re-surfaced.

I agree w/ tim, and i was able to get the full service manual direct from yamaha. And they shipped quickly. But the repair is not for the timid, and i had to have a new VSLI chip replaced (no socket).

good luck,
bob

[Phillip Huy]

Hello Tim and Mark,

It's amazing that I am able to write to you. I search the internet for help
for three days to find someone w/ solution to my protection circuit problem in my Denon AVR 681; I finally found your post! I hope you still remember it.

Please let me know if you finally fix the problem. I have axactly the same problem w/ mine.

Mark, please tell me why did you suggested to replace the bad resitor (R115/116), 1 ohm with a 0.22 ohm @ 1 w? Do you have or know where to find the service manual?

I would like to fix mine because it is a challenge and I don't like to fill up the land-fill.

Best regards,

Phillip huy

Tim Schwartz" <toschwartz@xxxxxxxxxxxxxxxx> wrote in message
news:42BB160F.710A72F9@xxxxxxxxxxxxxxxxxxx
> Hello all,
>
> I've got a unit here that goes into protection a few seconds after
> power up. I've got NOTHING connected to it, and the volume all the way
> down. The output transistors all ohm-meter OK. The 45 rail
> (approximate) seems OK. ALL 5 channels have about ? on them, which
> explains the protection, and indicates some sort of power supply issue.
> Any ideas?
>
> I don't have a schematic or service manual for this unit. Thanks for
> your time.
>
> Regards,
> Tim Schwartz
> Bristol Electronics

These get 1 ohm resistors bad in the regulated power supply area - need to
be changed out for .22 @ 1 watt.

Mark Z.

P.S.
Some models they are R115 and R116, not sure of yours.