Need help with CTC-87 -- snap, snap, snap

[jpdylon]

I rescued a cute little 13" RCA xl-100 with a CTC-87 chassis in it. It produces an awesome picture when its working...

However periodically I can hear some HV arcing. When you hear the snap, the picture disappears briefly, then comes back. I have checked the wire dressing, looked for arcing around the chassis and CRT socket - none found. I've cleaned the spark gap on the CRT board. THe CRT itself doesn't appear to have any shorts according to the tester and the flyback doesn't have any evidence of arcing to the chassis. I also can't see where the arcing is coming from in a darkened room.

One time I gave the set a large THWACK on the side which then made the picture white out and go into HV shutdown. However, I have not been able to reproduce that again. There were no obvious signs of bad solder connections on the boards but then again my vision up close isn't always the greatest.

No trippler in this unit. Anyone got any ideas as to where to go next? I hate to toss the thing...