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Not sure if this is your problem or not....
BUT, iIRC in late 1996...I have I think an NEC monitor, 19" or so...and nit had a BAD sync issue. That turned out to be the video processor. BUT..after it was replaced...the focus just was NOT quite right. There were 2 focus controls on the fly...but NEITHER ONE...would quite 'get it". Almost...but not quite. And I think it WAS worse--was near the sides and edges. For quite awhile....I thought it was a flyback, I think that was tried....and did not help. It seemed there just was something "missing".
that "something" turned out to be DYNAMIC focus. What happened...was they had sent the WRONG processor to us (tandy), where I was working at then). It did NOT have a dynamic focus output....and without it...the tube could NOT focus quite right all over.
The boss, was now able to find out a snafu had occurred and NEC or such sent us the RIGHT chip...but it was USED and being a large pin SMD chip...it was NOT usuable. This set him OFF...and he DEMANDED we be sent a complete BOARD--which contained all of the low-level stuff--since we doubted another chip could be transplanted ont the old one again.
That DID fix the problem !! GREAT focus all over. ANd the dynamic focus line form tha tboard to the H-0out ckty was again correct. There was PLENTY of "reserve" now left on the now new flyback focus controls.
So....see if there is a dynamic focus ckt. this very WELL may be your problem. It "modifies" the focus line--accd. to WHERE the horizontal scan is at any given time, on the screen. ALso...check your video bias supply voltage--if you hav enot already replaced the caps on that line.
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