PIONEER SC-LX 701/801/901

Update, have spent a bit of time looking at this. All main power supplies are fine with no noise, also checked all power on the main board 3.3 and 1.2 supplies, all clean.

I think I've narrowed this fault down to the audio board which have the input switchers and volume control chips. I suspected the +7 -7 supplies but they also check out ok. Zone 2 and Zone 3 audio work fine during the fault period when there is no audio on main zone, audio for these is processed on this same board using the same supply lines.

On the audio board there are two BD34704KS2 audio processors, these do bulk of input switching and and volume control. There are also 2 smaller chips which do volume for Zone 2 and Zone 2 which must be ok.

I could do with some help in determining the audio paths as it's very confusing trying to work this out just from the schematics. I'm used to Denon and Marantz manuals with good block diagrams showing all the flows. The Pioneer service manual is very poor in this regards. I know the BD34704KS2 pins 60 to 69 has DSP inputs but not sure which way signals are route, i.e. from source ADC into the DSP then DAC etc.. I could just replace the BD34704KS2 but would like to understand what's going on. Not easy as that board is 2 beneath main HDMI board.


Thanks

Hi


1) Pre-amp outs also do not work when the fault is there. Also no Sub out, this confuses me somewhat as Sub out 1 and 2 are split between the two BD34704KS2 chips, I would have expected one of the two Sub outs to be ok if my theory is correct but this is not the case.
2) SC-LX801 but according to the manual, Pioneer MODEL No.SC-LX701/801/901, Onkyo TX-RZ1100/3100, DRX-7/R1,PR-RZ5100,DRC-R1 are all the same in this area.
3) HDMI pass through works fine, ARC also fine (when problem not there).
4) Analogue inputs also have the same issue. 
5) Direct/Pure does not make any difference to the issue when it occurs.
6) One additional bit of info, all the speaker symbols in the display are always correct even when there is no sound. Is this another sign DSP is ok?

A little bit of further diagnosis, freezer on IC301 (BD34704KS2) does seem to recreate the problem and it lasts longer, but it's a bit hit and miss as it's not easy to get to it when the unit is fully assembled. Looking at the manual after these chips it's pure analogue all the way to the amps, there are some buffer stages in the path but the fact that Zone2 and Zone 3 work fine I can't see this being an issue on the amp board. Also when the fault is ongoing turning up the volume really high you can hear the source very faintly which also proves to me that all AD DA DSP most likely is ok.

Looking at sources for BD34704KS2, seems Farnell and Mouser have them but excessive handling charges.

I'm interested to hear your thoughts on why you think the fault cannot be the main BD34704KS2?

Thanks for your help Mastertech, hopefully we can both learn from this one. 

Update.... I2C signals leaving main digital board towards DAC during fault condition confirmed good.

Issue must be on the DAC board.