Sony KV-20TS27 20 inch TV tuner failure?

[rkm0]

I have a Sony KV-20TS27 trinitron TV, made in February 1992. It
displays UHF channels and the composite video fine, but doesn't display
VHF channels. Actually, it seems to display them intermittently;
haven't tested it thoroughly, but it seems that the VHF channels work
when the TV has been running for a while and heated up.

Is this a VHF tuner failure? How can I fix it myself? Perhaps something
as simple as a failed solder joint?

Thanks!