Sanwa PM1723C, loses V-hold when warm

[Arcade-Projects]

Hi, I'm working on a Sanwa PM1723C which loses V-hold when it has been running about 20 minutes.

It all starts out ok, but after 5-10 minutes the image start to twitch a bit. And after 15 minutes the image starts to roll vertically.
After 20 minutes it rolls so fast that I cant distinguish any graphics on screen.

I've checked all solder joints around the HA11235 sync IC.
I've replaced the V-hold pot
All caps have been replaced.
I've also socketed the HA11235 sync IC and replaced it with a known working one.
No difference at all.

Any pointers at what to look for?
I'm going to buy one of those air-in-a-can so that I can flip it upside down and shoot some ice cold air onto some areas of the chassis handling vertical sync.

I attached the schematics for this chassis as well.
Thanks

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