A few things to check but its a small chance.
1) On GE sets always resolder the UHF IF link & the tuner IF
out cable. The RCA jacks are just crimped on & go int.
2) Make a crude tuner subber to double check the IF.
Take any old solid state VHF tuner & give it B+. Hook to IF input
cable. You will at least get snow if the IF is running.
3) with a signal & a GOOD scope you can trace through IF's looking
at the undetected video.
73 Zeno
LFOD !