Comb filters came out apx 1978 on Magnavox. In all the years since
then I never had to repair or adj one. At that probably change all
the electrolytic caps in that part of the circuit. Beyond that post
just the part of schematic with it. Someone else may have ideas.
Comb filters were unsung heroes of TV. You could demo one beside a non combed set & instantly up sell the set from $50 - $100.
73 Zeno
LFOD !