Yamaha RX-797 problem...opinions?

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Hi guys,
New guy here.
I have a problem with a 2.5 year old Yamaha RX-797 Receiver.

All of a sudden, it will not produce any sound unless the "pure direct" button is enabled.
Essentially, this bypasses all tonal control, balance control, etc.
With the "pure direct" enabled the amplifiers work wonderfully, but with no control of tone/balance of course.
I would guess this indicates a problem in either the tone control sub-board, or the "pure direct" sub-board?
Mother Yamaha cannot even recommend a repair facility, or even let me know if there are any T.S.B.'s on this problem.
A Google search yielded a few other people with this same condition in their RX-797, but so far no one has posted any replies on if this is a known problem, etc.
Anyone?
Thanks in advance... :)
 
With a schematic, the best thing to do would be to try and sniff the signal as it goes through. A pair of cheap headphones would do, wire the ground to signal ground, and take the tip of the plug to a probe you can position on the circut. Play a sine wave or something into it and see where it disappears.

A scope would be better for that of course ;)

Of course, I'm also assuming your skills are up to this kind of work. You would have to have the case open and the amplifier powered, so there's a risk.

If you're looking for something quick to try, see if you can find a replacement for the Pure Direct switch and simply try replacing it. You could remove the switch and use wire to hardwire it in the "on" position if you wanted.
 
pure direct bypasses the DSP board. you either have a bad DSP board or are missing one of the power supplies that feed it. pure direct is one of the troubleshooting steps for determiming whether the problem is with the DSP board or elsewhere, at least on yamahas. other manufacturers have other ways of bypassing the DSP for testing.
 
PM650.
As I am a new member here, I am not yet allowed to email current members.
Please if you have time, email ME!;)

I had the audio board and switch board out to check for switch operation, and cold solder joints, etc....everything looks fine. I figured out the operation of the switch, and it mimics the other identical "direct CD" switch next to it.
But, w/o a manual or schematic I am looking for the "needle in a haystack".
If you have time, please email me.
Or any other members here that see this please email PM650 to tell him I cannot as yet contact him.
Thank You!
 
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