Did you get this sorted?
If the game plays with random garbage on the screen like shown, it's very likely to be RAMs going duff.
Do the self test and it will tell you which RAM is bad via the LEDs on the main PCB. Your machine should have the diagnostics sheet stapled to the back door which tells you the location of the defective RAM. Swap it with another one off the board if you don't have a spare and see if the fault moves to the location you swapped the bad one to. If it does the chip is deffo bad. If not it may be something more tricky!
I've had to swap 3 RAMs in my Qix so far over the last 3 years. Only last week I had garbage on screen, playable but no sound. Swapping the RAM out solved both problems (thankfully, cos I love my Qix!)
Hope this helps.
Jase