monitor problem

Hi all,

I have a gateway 700A monitor which is dead. At first it was just "ticking"
about once a second, I found a shorted line transistor which I have
replaced. Now it makes a odd "zip" sound, sounds to start at a high
frequency then slop down fast in about half a second, then goes off, then
comes back a second latter. Seems it is tripping out for some reason. There
is no heater voltage apart from the time where is making the zip sound, then
it jumps up and goes off again. Sounds to me like the LOPT is faulty ? I
dont think they can be tested, only think ive done is check the HT cap to
ground, which reads something like 1902 on diode test, so it don't seem
shorted ? I've checked most of the diodes and transistors and higher wattage
resistors and haven't found anything apart from a slightly duff solder joint
on a diode which goes to the collector of the transistor I changed, any idea
what else I can check before I resort to lugging it into work to be checked
?

Thanks
Chris