Although the LOPT might be defective, the control signal of the HOT is at
least as suspective. You hardly can check this out without an
oscilloscope.
You need to check the frequency and the pulsewidth. The pulsehight may
give
you an idea whether or not the pulse has enough power to drive the HOT
correctly. A positive DC level (p. e. caused by a leaky driver
transformer)
will be disastrous for the HOT. For maximum certainty you'll need the
specs
of the manufacturer.

One particular Thomson chassis of the past comes to mind, the
TX-85/86. A 100 ohm, 35 VDC capacitor goes bad in the drive circuitry
(which used no drive transformer, by the way). The DC voltage starts
to float up from the desired -2.25 or so VDC, the negative spike's
peak rises to about -8 from -11, the HOT runs hot, and eventually
dies.

Dear Tom,

Thank You again. I have ordered several new capacitors to replace the ones
in the drive circuit. Perhaps I will replace some more (why not all of them
(well, not on the processor board maybe but I mean the ones on the large
signal board), they're not that expensive). I will also re-connect my scope
to the machine and see how much the shape of the wave differs from the one
in the service doc. And check whether there is a DC-component behind the
transformer.

Greetings,
Rene