snip

The upper drum(s) can only go on one way. It has a pilot hole for a
guide and the screw holes are also slightly offset.

Don't know what happened, but switching them fried something in either
the units themselves, or in the upper drums.

*Both* units with their original heads have video, but the audio is
muddy. I cleaned both using the fingernail method you mentioned,
followed up with paper and alcohol, no change.

Oh well.........



OK. Well the offsetting of the screw holes is what I had expected, so I
really don't know what you can have done. I can't think of any way that
either set of heads, let alone both, can have been damaged by simply
swapping them between machines. Even if one set had much more 'robust'
windings to take a higher bias current on record, they should at least have
survived in the other machine. It's been a while since I did much work on
VCRs as they have not been popular here for a couple of years now, but
'muddy' is not a description that I would normally have found a way of
putting to a hifi sound track. Usually, this track has a tendency to drop
out completely when the heads wear, and the machine reverts back to the
linear sound track, which can be muddy if the A/S head is not properly
aligned. You said before that you had altered the setting of the supply
guide roller. Have you tried making sure that you have that back in exactly
the right place ? As I think I pointed out earlier, correct recovery of the
hifi sound track is critical of several factors.

Arfa