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Pre-show testing uncovered that the LOPT was cracked in three places with blue HV haze crackling along them. The monitor was still working with a good picture, however. There were no reproduction LOPT's for the WG4600 but a fellow local collector, Dok, had a spare. Given the separate side-frame mounting, the LOPT was replaced in situ without needing to remove the monitor and the replacement LOPT worked OK.
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In the cabinet the game PCB didn't boot with garbage display. On the bench there was a blank white screen. The scope showed there was video sync and colour blanking. IC 9C (2650 CPU) pin 16 RESET was pulsing consistent with the watchdog firing. The Arduino ICT reported RAM and Interrupt passing OK. "RAM Write All AD" showed reasonable looking graphics. Swapping in a new 2650 CPU brought the game to life and a quick cross check confirmed that the 2650 CPU was bad.
In the cabinet the game PCB showed a white screen except for a single sprite that was moving consistent with the game running in attract mode. On the bench, the Arduino ICT "RAM Check All" test flagged "E:3E 1500 91 FF" suggesting IC 3E (2636) was bad. Both of the other two 2636, ICs 5E and 2E, passed OK. To confirm that there wasn't a chip select issue I swapped IC 3E with 5E and the failure followed the IC. Replacing IC 3E (2636) fixed the game.