Zenith ChromaColor II 19KC52 won't power up (long msg)

1)
Months ago when this set was still working, I noticed that when we powered it on with the ON button on the front panel (that is, not using the remote to power it up) that we had to try repeatedly to power it up. At tht time I thought the switch was wearing out.

I'd press the switch and the set would try to power up, I'd get an instant of sound and maybe a slight disturbance in the screen (say black changing to dark gray). If I pressed the switch again the set would power up.

I'm referring to the power switch behind the front cover, not the circuit breaker.

2)
I tested the primary rectifier diodes on the plug-in circuit board (think it's 9-122, the board with edge contacts that plug into a finger socket on the chassis) and the diodes measure like good diodes, not shorted.

3)
I removed the horizontal output transistor and measured all combinations of one terminal to another, and found no indication of a short. I can't say it's free of leakage, but my DVOM on diode and on resistance ranges shows no short. I did not yet try to power up with the HO transistor removed.

4)
The 24V regulator was not shorted to GND (as I recall I tested this, but I don't have my notes in front of me).

Thanks for your continued assistance. I'll repeat some of my measurements and try to power up without the HO transistor.