Sony PVM-1442QM problem

[naujoks]

I have a beautiful Sony PVM-1442QM, which has developed a problem out of the blue.
When switching it on, there was a hissing sound and the power LED went from bright green to dim green after 2 seconds. No picture.
Opening up I could see no blown parts.
I swapped the power supply board from another monitor, same model, and it actually came on again.
I didn't use it for a couple of weeks and when I switched it on again today, the same symptoms as before were showing. The power supply board is good, I checked the voltages and tried it in the other monitor.
I switched on the monitor, leaving it uncovered to try and see/hear where the hissing sound is coming from, and I could see some arching and the smell of ozone (lovely!) coming from Q501 on the main board, which I think is the HOT.
I took it out, measured it through, but it seemed fine. I replaced it with a new one (2SD1397), but it didn't fix it.

Any ideas what could be responsible for those symptoms and what else I could check?

[inse]

Mmaybe the FBT is cracked and there is a HV discharge.
Might be intermittent in the beginning.
Run the set in a darkened room and look for arcing.