Stargate and Bubbles both fixed

Stargate had been working OK for all of a week, then it popped up with the vertical lines through the screen issue. Searching the forums mentioned forcing the game into cocktail mode to determine if the problem is the shift registers. I did that first, the the game did indeed go into cocktail mode, BUT, the lines were still there. The game would throw up a RAM error only in test mode but never in game mode. Swapped the RAMs and no change. Swapped video decoders and no change. Probing the outputs from the shift registers with a scope showed that 4I and 4J had outputs that resembled a clock signal, while the other 6 shift registers showed bursts of data. On a whim, I took a spare 74166 and piggybacked the register at 4I. Presto, problem solved, vertical lines all gone!!. It appeared that 4I and 4J were both bad, which is why putting it into cocktail mode didn't change things. I verified this by checking the outputs from 4I and 4J after swapping in the new chip. The output from 4I now looks like the other shift registers, while 4J's output looks like a clock signal.

As for Bubbles, it was stuck in cocktail mode, so when you'd play a 2 player game, on player 2's turn, the screen would flip upside down. Swapped the CPI board and the problem was gone, so it was probably the 6821 PIA chip on that board.  That's enough repairs for this weekend. Time to play some games!!