From Zenith 1978 parts catalogue
63- 4906 Unlisted ( often available til stock is gone) , no sub
63-5494 Listed, 41 cents, no subs.
I would put a pot there. IIRC fringe lock ( also on Motos ) have
to do with the RF AGC but its been a LONG time ! Adjust per Sams.
BTW some NOS VDR's are going bad in the pkg
73 Zeno
LFOD !