VECTOR: Go5/801 probs (Asteroids)

Hi,
my first post, so bear with me,

i finally got my Asteroids cab working after re capping etc.. only to lose the "Y" axis after two weeks, i took out the deflection pcb and after metering the TIS98 transistors i found Q601 to be duff, i replaced this and it then meter'd fine, but still the same prob, so i took out the large heatsink and replaced Q607 and Q608 although i had already replaced all four (both "X" and "Y") during the rebuild, but still the same prob.
All i have is a horizontal line across the screen, which you can just make out is the game playing, i have two working game pcb's and it gives me the same fault with both, so i'm pretty sure it must be something to do with the deflection pcb. 
This is my first vector game, so any advice would be welcome....


Thanx in advance,


Pinx