Thanks guys, here is what I did, since I have my Galaga machine on a bench in my garage, and the main board is easy to remove, I figured I would practice on this one first.
It has a similar issue with screen problems so I figured if I could fix this one simply I would be miles in front, and if I buggered it, well its probably an easier fix than the Sega.
I rummaged through my tool box and found a small screwdriver that was fairly blunt and went to work on the galaga board.

Firstly I wanted to completely remove an eprom to make sure I wasn't doing damage to the tracks underneath, turns out the eprom sits pretty high so unless you go mad and jam the screwdriver right in you are pretty safe.

Carefully replaced the first eprom and went around and slightly lifted and reseated the rest of them.
They gave a satisfying creak sound as they re-seated so sounded like it was all good.

Put the board back in, plugged her in and waited expectantly while the old tube warmed up but alas, still the same as before.
Oh, well, maybe i didn't re-seat them enough I thought so pulled the board back out, lifted them again and went back to eprom number one ( the one I had pulled out completely). Once I pulled it back out I noted to my horror I had bent one of the legs when I put it back in the first time.

I carefully straightened out the bent leg, and extra carefully pushed it back into its socket.
OK, now it ought to work, plugged it back in, wait for screen to warm up, but same as before.

Not sure what is up with the galaga, could be something is burnt out on that board. I did note when I put a multimeter to the +5v supply (at the power supply) that I was getting 5.4 volts and at times up to 5.6volts, not sure if the power supply is supposed to run at dead on 5volts all the time so maybe this is part of my problem.
Here is a pic of what the screen looks like.

Cheers