Just picked up a W800 (S$20, but I have no idea how much these are worth). Silver tuner version. Condition is pretty decent.

Rebelted Deck B and proceeded to test the amp.

Unfortunately, while everything powers on and works, I get absolutely no sound from the headphones at all. No crackle, hum or anything. On both decks. I've checked the position of the rec/playback switch,volume pot, and all the leaf switches. On a glance the headphone port looks fine. Is there a muting circuit I'm missing out?

Another reason may be capacitors, although I see no signs of leakage.

Have you tested the caps? You could try and wire another cap of similar or larger size in parallel over one of them to see if you get any response. I had a similar issue with a PX10. I continuity tested all the way back the whole channel to find it was the cap in the end.

I've tried replacing all the 220uf caps and some of the others (quite a large variety of strange values here). Still nothing. Any WM-W800/10 owners here know if there is anything else I'm missing? If any of you own a WM-W800, is there any sound from the headphones when in recording mode?

Have you been able to test the traces of the audio path from the tape head > pre amp > power amp > headphones? I know you've said you've replaced the post amp dc blocking caps, but what about the pre amp caps? Are they ok? What about the condition of the traces around the pre amp / power amp? Check for cold joints or even cracks on the traces. For all of this you will need to get probing with the continuity meter and maybe look very closely with the magnifying glass too.

It is frustrating to diagnose these kind of faults. I've got a unit here, that I think I may well have to strip right down again to board level for the third time just to find an intermittent short out. I've already fixed a load of cold joints on several surface mount resistors on it.

It is worth fixing in the end though, as the W800 is a unique walkman with its double tape deck feature.