If yours has the board shown in post #3 that's likely the cause of no hifi audio. Those silver SMD caps are bad and leak and ruin traces. There's also one on the bottom of the head drum. If I get everything up and going on this I'll probably recap the power supply as it runs hot
is that one the actual audio board? mine has it and, looking at the inside, that 6700 looks a lot like my 4700... maybe the basic design is the same and they share a lot of things?
regarding the power supply....
years ago, when I started experiencing issues on HiFi Audio, I had tried to replace the audio CMOS switches chips but nothing changed then I did put it aside...
and trying it again a couple months ago, it was totally dead... then I removed the whole power supply (that metal box above the mechanism) and I tested a couple capacitors (i.e. the 100uF 400V one) and they were dead... also, the bigger brown ELNA capacitors leaked a lot of brown crap which corroded some tracks and, also, that crap seems to also be somewhat conductive.
While trying to check/troubleshoot it after replacing the capacitors, surely something else got broken then I fear I'd need to replace quite some parts.
At the moment, the power supply is still outside the VCR and waiting for the tricky and long work needed to fix it... let's see how it goes.
I am tempted to buy one of those small component tester devices, to be able to check more parts.
Anyways, If yours powers up correctly, I would immediately recap the power supply before risking that those ELNA leak that crap and make a lot of damage... I mean all electrolytic caps in the power supply should be replaced as soon as possible.