I have a TV with no vertical deflection, just the horizontal line
across the center.
It is a Panasonic PV-27D52, chassis KM-D2702, from 2002.

I checked the supply voltages to the vertical deflection chip
(LA7837).
Vcc (pin 1) was 23V (should be 12), and the pump-up supply voltage
(pin 8) was 28.4V (should be 24).
I removed the chip, and Vcc went to 11.8, and the pump-up V went to
29.4.

The pump-up V is derived from the flyback. The datasheet says it is a
nominal 24V, with 27V max. So I assume 29 is too high, and I
shouldn't just replace the chip without locating some other problem
first.

I have been checking all the diodes, caps, and resistors in the area
(with a DMM and with a simple ESR meter). I haven't found any that
read bad. I replaced a few borderline caps and one of the diodes.
Nothing I have done has any effect on the two voltages.

Any suggestions on where to look more specifically?

Thanks for any suggestions,
-Steve