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There had been a colour fault on this game PCB since it was acquired that cleared after a few minutes of warming up. Pre-show testing found the fault had become permanent. Starting with a video probe, checking IC55 (LS175) found pin 10 GC1 output with noise fading in and out. Input pin 12 was a wavy sawtooth with drifting levels. Checking IC57 (74S201) pin 6 was similar and the display changed if the IC was pressed. Black oxidized IC pins were cleaned but the colours were still bad. Replacing IC57 with a compatible 82S16 fixed the game.