+43 Volt Error on a Alltek Systems Replacement MPU Board

So I was helping another collector in the area try to get a Bally Star Trek Pinball running. It had a Alltek MPU replacement board it in that would start to boot but then stop with 5 diagnostic flashes which indicate a problem with the +43v supply. However, when tested at the test point, the +43v looked grossly normal.

Got in touch with Alltek Systems support and the person suggested disconnecting the sound board and seeing what happened. The game came up with it disconnected, and the support person said there was something wrong with the +43v stuff on the sound board. Right where it comes in there is a diode (CR3) that tested open one way, and about 94k ohms the other.

So a good diagnostic step for this kind of hardware, perhaps even with the original boards in it, is to completely disconnect the sound board and see if the behavior of the game changes.

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