FIXED! Onkyo TX-RZ710 no TrueHD, DTS-MA or multichannel PCM

Some further testing. All voltage test points I can get at measure OK, although the +12VST/DG line (pp 56 & 57) reads 12V from the standby supply board, but rises to 17.5V when the main transformer is activated. The manual says this should be 12-15V so it's a little high - but the AC output of the transformer that supplies this (P57) measures around 14.4V RMS, which fully rectified gives around 18V DC, so it's difficult to see how it could be expected to be as low as the manual says. Any ideas on this would be most helpful.

I then 'scoped HDMI_LRCK at pin 101 of Q8401 - a stable square wave at 192KHz for HD audio, and 96KHz for PCM 2-channel and other formats, which I think is what I'd expect. I traced this through Q1005 to DIR_LRCK (pin 18) and then through Q3404 to ADSPI_LRCK (pin 59). DIR_LCK was a stable 192KHz / 96KHz square wave, same as HDMI_LRCK. But while ADSPI_LRCK was stable square wave at 96KHz for 2-channel and other formats, for HD audio at 192KHZ it 'blips' regularly at just over 1 second intervals. By "blips", I mean I think it goes flat for an instant as if something is being reset, but it's too fast to catch on the scope what actually happens.

It may be this 'blip' that's stopping HD audio (and multi-channel PCM) from working but that's about as far as I'm able to go without some help.

Update: Been off with the 'flu for a couple of weeks. Anyway, I was poking around with the 'scope probe today, following HDMI clock signals from the HDMI transceiver to DIR / DSP and DAC, and suddenly got audio from DTS-MA for a second or two. So, thinks me, not a firmware issue, and not a failed component, must be a connectivity issue somewhere. Poked around a bit more and got the HD audio back again. Tried various formats and they all were working. Checked the AVR display and had DTS-MA in and out. But then I changed sound field a few times and the HD audio suddenly sort of squelched out to silence.

I examined the board very carefully under a strong light and found some green corrosion where the HDMI Main and HDMI Sub output sockets join the board, possibly between some of the 19 pins. I also found that wiggling those HDMI connectors, while it didn't restore the sound, did sometimes cause the video to break up or go pink.

So I removed the HDMI board, cleaned off as much of the corrosion as I could with various cleaners and a stiff brush (I used brake cleaner solvent, electrical contact cleaner, WD-40 and then 100% isopropyl alcohol). After that, I reflowed those HDMI sockets to the board with a tiny bit of solder paste and lots of flux, and then cleaned them up again, scraping between the pins with a scalpel.

I've just put it back together, and DTS-MA, Dolby TrueHD and LPCM multichannel all now working. I hope I've fixed it - I'll need to 'soak test' it for a bit to make sure. If it doesn't stay fixed, at least I've got some more clues as to what to look for.

But if it is actually fixed and stays that way, I'd be very interested in any thoughts from the experts as to why corrosion (and possible some intermittent contact) between the pins of the HDMI OUT sockets might cause HD audio loss, where other HDMI audio and all video formats were fine.

How badly cracked? I've repaired cracked boards before by straightening them out, then on the broken traces, scrape the green insulation back a bit, flux & tin the exposed copper and solder a bit of fine enamelled wire across the crack. Use the soldering iron to burn of the enamel and tin the wire at the correct pints to line up with the exposed traces. If more than one adjacent trace is broken and they're close together, stagger the exposed traces so solder can't blob from one trace to the next. Then check continuity and when all ok, cover the repair with epoxy to stop it flexing there. Double-sided and multi-layer boards are of course a lot more difficult. If you'd like to post a photo of the cracked part of the board, I might be able to say whether a repair looks feasible or not.