Start easy. CLEAN the AFC & band switches first. Then set to normal & V-U.
( ota settings). NOT HRC or IRC. NOT spcl.
Cold joints are possible. The TUNER itself is on the 9-151 board. Watch
the shield for cold joints. It completes ground paths.
The SELECTOR ( IIRC 9-165 ?) its the board up by the key board. Watch for
cold joints on shield & plugs ( not edge connectors ).
There is a 3 legged IC ( 5V reg ??) on the shield, check VDC both when running normal & acting up on all pins & see if it changes. Had a run of bad ones on the SM1971 sets but different symptoms. We sold a few dozen of them & most failed in a few yrs.
Now to the 9-160 PS/HV board. All voltages come from here. Half of the
fails are cold joints. Go over it real good especially under large parts.
There is a little transistor called 32V current source or something like that.
Be sure its putting out constant 32 VDC. Its the tuning voltage source.
With that said it sounds like the AFT is searching & not finding the horz pulse
to stop it. I should have the SAMS so I can pull it if need be. Keep us
posted. A u-tube would help also if you can.
73 Zeno
LFOD !