I have owned my Mary Shelley's Frankenstein since 1998. The only major repair was the DMD.

I was playing it last week, and in the middle of a game suddenly showed garbled partial graphics on the DMD, and there was a loud hum. I immediately flipped off the switch and unplugged the machine.

I tested all of the fuses, and none were blown. I disconnected the connectors from the power supply. I verified all of the incoming voltages. I reconnected the input to the power board, and verified all of the output voltages. So unfortunately, it doesn't appear to be a power issue.

If I reconnect all power, I get the same pronounce hum. The hum is NOT coming from the speakers (I disconnected them to be 100% sure). If I disconnect CN6, the hum goes away. CN6 contains -12V, +12V, and 5V. These go to the sound and CPU.

Is there any chance this is NOT a problem with the CPU board? I am looking at https://bayareaamusements.com/Merchant2/merchant.mvc?Screen=PROD&Product_Code=PC-MPU004 and it mentions Frankenstein. My manual has a part number of 520-5003-004, but the site lists this as a replacement board for only 520-5003-001, 520-5003-002, and 520-5003-003. What's the difference between 520-5003-004 and the others?

Are there any common components on the CPU board that have a history of going bad? What are my next steps?

True.

No sound from the speakers. When I power on, it usually says, "Frankenstein!". Now I get nothing.

It's not the DMD. I replaced the DMD with an RGB DMD a couple of years ago. And yes, when it was the DMD, it powered up and was playable.

I resemble that remark. I have ripped out more than one eyelet in my lifetime.

FYI, according PinWiki, it appears some were labelled as -04 from the factory, but were actually -03. It doesn't say it outright; but I think they are the same.

http://www.pinwiki.com/wiki/index.php?title=Data_East/Sega#The_Data_East_Board_Set

Good news. I went to do some more diagnosing. I powered the machine on a couple of times. And I DID get the "Frankenstein" greeting, and the DMD displayed correctly. Basically, everything appeared to work (for the few moments I had the machine on).

That means the CPU board is good. The sound board is good. The DMD is good.

That means it is almost certainly a voltage issue. I got some readings on the TP on the CPU board during power up, from 4.6v to 4.9v. I know these machines have a history of being finicky with their 5 volts.

So maybe old caps are degrading.

Problem found.

Diagnosis was made harder because I forgot that the LED kit I installed came with light strips that connected to 12V. THAT was the problem. The light strips were drawing so much current, the 12V (unregulated), dropped to 8V and the sound board malfunctioned.

I thought this voltage drop was a power supply issue (because that 12V is only supposed to go to the sound board). So I bought a power supply cap kit for about $25.

I disconnected the LED strips and all is good.