thanks to a floppy disk rescue --- was it Ried?
Yes, it was Ried... (thanks dude!)
The early video board schematics list the 24V linear regulator as the lower current (1A) variety 78M24. The Rev F schematic shows the change to the 1.5A variety 7824.
I too have had to replace a few of these regulators, which is a bit of a surprise since they have a lot of built-in self-protection (thermal, over-current, and SOA I think). IIRC, the datasheet warns about reversing current through these (eg. via a big cap on the output that discharges back through the regulator when power is removed), so maybe a reverse-bias bypass diode would help.
On the other hand, they take a long time to fail, so perhaps it is just accelerated aging due to temperature and a larger heatsink is what is warranted. In the 70s & 80s, it seemed common to have manufacturers apply a substantial (sometimes huge) amount of thermal grease when attaching heatsinks, but investigations showed that less was in fact a lot better, and that the quality (flatness) of the surface also has a big effect.
Note that the adjustable coil L3 was removed in later versions of the video board (and it didn't seem to have any effect when installed), so if you find it half-broken you can remove it.
I've also had to replace the BU-406 (Q5) on a few boards.
As for the trim-pots going intermittent, I haven't attempted to determine if that is a rating issue, or if they just age. The vertical hold often seems to go first; perhaps because that's the most noticable thing, or perhaps thats a current/voltage thing. Wiping them back and forth a few times or slightly moving the position is sometimes enough to have them work again for quite a while.
