Same problem I didn't work on since a year ago!
(I didn't want to take the set apart until I had the replacement
transistor in hand.)

Helped by this group, I replaced Q4402 (H-Sync emitter follower/buffer)
but no change.

Now I have looked at emitter & base of Q4402, as well as Pin 23 of
Controller U3101. All waveforms agree with the service manual.

Any further suggestions?

My original post was as below:

The ProScan 27" set with CTC 169 [AJ] chassis is over ten years old.
Recently onscreen display started tearing; after an hour or so of
"warmup" it would be OK.
Now it never displays properly. Video modulation comes through.
Horizontal sync is the problem; vertical is OK.
I have the Field Service manual, which says "The OSD horizontal
position
is phase-locked with the H-SYNC signal at Pin 23. . . . Components
external to the micro at Pins 25 and 26 set up the characteristics of
the OSD PLL."
Pins 25 and 26 go to 2 resistors and one cap to ground.
This set is a mess to work on. If I am sure that it's one of these
three parts, I'll do it. (Otherwise I'll just forget about the OSD!)

Any suggestions?
Thanks -
Matt Baum
Expert in the obsolete!