My centaur MPU (alltek) fails to boot if any switches in a certain return row of the matrix are active on power up. Repeatable when a different alltek MPU is swapped in, so the issue is under the playfield and not the MPU. A couple of these switches are on drop targets, and I'd rather fix the issue than remove the glass to manually reset drops before turning it on.

Everything *looks* ok at the switches. And I've tested all the switch diodes in circuit and they seem good.

A few of the switches have ceramic disc capacitors, my multimeter does not do capacitance. Can a failed disc capacitor on a switch cause something like MPU boot fail? If yes, then I'll just order some and replace to see if that does the trick. If no, is there something else I should be considering?
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You are awesome, thank you! You guessed correctly, I had a flicker plus three flashes. Inspecting all the switches on the row for lank shorts, I found the top middle lane switch bracket to be grazing the ground braid for the lamp. Bent it away with pliers and the issue is fixed!

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It has a repro play field, I believe. Or a very well touched up and clear coated one, but I expect the former. The previous owner didn't really have the space and sold it with only a couple games on it after a full restore. Not enough to even notice the issue. Very lucky local find for me. I have a couple switches to adjust, and the sound pots to replace, and then it's pretty much a brand new centaur.