I know this sounds like an ancient Egyptian meets robot affair, but I’ve had something happen that I’ve never seen before.

Yesterday I noticed that pharaoh was not turning on, so digging into this I saw that the line fuse has blown. Fine, no big deal replaced the line fuse with a 7a fuse just to see if it blew again (line fuse is 8a on system 7). I turned the game on and saw a puff of smoke and it seemed the varistor had blown. I think it was blown the first time but was stapled under a piece of cardboard so not easy to see. easy enough I have seen this before, I pulled the whole transformer board out of the game to isolate any impact and replaced the varistor, just to have it violently blow again when plugged in.

I continuity checked the line filter, no shorts. Power cable looks fine, has ground plug, though it is older. What am I missing? No recent work has been done on the game, the outlet tests fine.
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Yes it is from a Bally rectifier board! I did find a post saying that a fathom was the same as another system 7, so I made an assumption that they were all the same. Thanks for the help