> Turns out the approximately line frequency noise was somehow caused by th=
e
> smpsu's in the vcr's somehow interacting when enough self made RFI was pr=
esent,
> likely mixing in one of the input circuits together with some servo pulse=
s
> related to the head sync. The problem disappeared when the VCRs (any two =
from a
> stack of 3 !) were separated by more than about 5cm/2in. There was no roo=
m in
> our rack for such separation, we had built it around the nice form factor=
 of the
> carefully chosen brand name VCRs...
>
> The problem was 'fixed' by replacing the vcrs for another brand, also Far
> Eastern, and changing nothing else. After that, it worked for years.

Sliding in a thin steel sheet between VCRs,s may have been enough -
possibly perforated if airflow an issue.
Sliding in a thin mumetal sheet would definitely have helped, but new
VCRs probably cost less than such :-).

      Russell
--=20
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