that can be a tricky problem to track down.
verify that you have all the correct caps in the correct location and polarity.
give the chassis a good re-flow, they suffer from lots of cold solder joints.
if your H.O.T. is good out of circuit and your bulb is good, then it is most likely something in your horizontal section shorting to ground.
if you need it fixed, your welcome to send it in.
Peace
Buffett