SONY Trinitron 27" TV model KV-27T530.

The generic remote doesn't work.

The SONY TV's own remote was stolen years ago. Since generic remotes
work I did not miss the stolen one.

The SONY remote [from the stereo amp with controls for
audio/TV/VTR/LDP] System OFF button works. This remote's TV ON/OFF
button works. But channel # select, channel step up/down and volume
control don't work.

If the SONY (but not the generic) remote ON/OFF works it likely means
the IR photo receptor is good. Yet it won't accept channel select and
volume signals from any remote controller.

Any suggestions what to look for next?

My plan of action is to remove the TV control panel and look for cold
solder joints. A general cleaning then reseat the connector plugs.
There is no circuit diagram although the function blocks are IDed on
the single main PCB.

I can live with without the remote. Picture quality and sound is
still excellent. The TV set is too bulky to take to a TV repair shop.
Its not worth repairing anyway. The money will be better spent on a
new flat panel TV set. I can fix most things including TV sets if
pointed in the right direction.