Only one channel with optical/coax connections?

Perhaps I originally posted this question in the wrong forum since I have received no replies. Yamaha receiver, RX V3000, no audio from left channel when using digital/optical input. Analog/RCA inputs work as they should, provide sound from both channels. Different digital cables give the same result. Input is set properly. Burr Brown DACs, 1704. Do these tank over time or could there be another issue? Where do I begin to trouble shoot? I have compared multimeter readings from one good identical Yamaha DSP board to the one in question, and all appears to be consistent. I am stumped. Any ideas?


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If iy has a "cost" (RCA) digital input - try that?

Eventually the digital signal ends up in two traces on the PCB as in L&R channel - either tre is someting broken in the DAC or some analog path problem leading up to the main analog bus in the amp - which works as your analog RCA is OK...

There is noting bad with the optical cable - if one ch works, the other is ok ;) as both channels are serially interleaved on one physical bearer.

This thing is making me crazy. I have a second DSP board from another unit that works fine. So I conclude the problem is with the DSP board. Using the multimeter, therefore, I have tried to check and compare 'apples to apples' each component- ICs, capacitors from the bad board to the good board and all seem to be consistent. I have continuity from the DSP chip output all the way to the final capacitor...but no sound. I have run through the onboard diagnostics and double checked all settings. I suspect there's an electron gone berserk in the chip that is shutting down the left all modes...stereo, dolby, movie effects...all of them. I have not found a reset procedure other then turning it off and on...I would appreciate further help. Have to go now...there are two fellows in long white coats knocking on my door. They are holding a strange looking jacket and say they are here to help......
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Yes, through the main channel audio from stereo CDs, or DVD movies in any of the dolby or special effects settings. I have continuity from the DSP chip through the l left channel signal path and the voltage readings (IC525, 526, resistors, etc) along that path are on spec. This is a bear. I have checked and compared every cap and resistor on the bad board to the good one and found nothing a miss.
Well this is making me crazy. Comparing components board to board- good board to bad board- show virtually identical reading. Yet, the board in question has no left channel. As I have mentioned before, analog RCA inputs work fine. Putting the bad board in different receivers still has no left channel. Problem has to be on the DSP board...but where...? Where???
Exactly...and so far as I have been able to determine, each component on the bad board provides the same readings as an identical good board.
but I have surely missed the faulty component...incidentally, the bad board is missing the left channel even when connected to another good RX V3000. This further proves the board is faulty not the receiver. And again, RC inputs work fine. Not much left except the DSP chip and I don't understand why it would give just one dead channel....I would expect everything to be dead with a bad DSP chip.
Shouldn't be this tough. Two identical Yamaha RX V3000, two identical DSP boards. Sitting side by side with two identical coax inputs at the CD connection.
Voltages measurement through the signal path at the same component points- input and output- on both board produces virtually identical results. And DSP board has only the right channel...while the other has both left and right...WTH???
A scope would do but looking at the schematic pretty much everything takes place in the YSS928 DSP. The digital inputs, both optical and wired, go straight to the DSP as does the digital output of the codec. Given that the digital filter and the two dacs work, the only place a channel can goes missing and not affect anything else is inside the DSP.
Interesting part to me is that the various 'effects' 'theater, hall, church, jazz, concert, etc provide audio in both left and right does a movie or whatever in pro logic mode. Turn off the 'effects' and it is right back to right channel only. I would have thought a DSP fault would produce no sound in either channel. But yes, more or less has to be inside the DSP...but what to do? Drag out the heat gun... and destroy everything???
I walked away and settled for what I consider to be an inferior sounding DSP board. But I refuse to give up the situation is that RCA analog connections provide left and right channels. The various 'effects' provide both left and right channels through the digital connections...but there is no stereo from optical or coax...the left channel is dead. There has to be a way to diagnose the bad component...but how???