Were some low voltage and some high voltage?

Im not sure really as stern pins are not my specialty and havent really had to work on any lol. I know stern went to low voltage displays around 2012 /acdc . But original iron man sld be the same high voltage as any other plasma dmd used from 1991 till acdc so not sure what u have going on without being there

Im so confused lol .... it sld be standard high-voltage display but if you were using a newer red led display than something had to be modified i believe for it to work?

Do you have this board in your backbox? If not than its low voltage and Regular plasmas wont work.300px-Stern_WS_DMD_PSU (resized).jpg

Any chance the ribbon cable is pluged in wrong? Is the red strip at pin 1?

I have no clue if anything im coming up with even makes sense .... i need to sleep lol been long long day . Good luck

Might have some high voltage power issues going on. Either too low or too high. Some displays are affected by over or under voltage differently. Some are not affected at all. If you have another Stern game, try swapping that board.
-Jeff

What ended up being the issue?

The standard 128x32 orange plasma displays are interchangeable between all game manufacturers.

The problem could be that the old display may require a bit more voltage to get it to display properly. Not really much you can do if the HV board is providing voltages within spec. You can try to reseat the two connectors on the HV board just to make sure there is a good connection.

As someone mentioned, the ribbon cable has a red stripe and should be oriented so the stripe is at pin 1 at both ends. Typically you won't get any activity on the display if the ribbon cable is not seated or installed backwards.

I had a similar issue. I purchased a colorDMD for my Spider-Man (2007, Stern) and moved the original DMD to a Williams T2, which had a DMD on it's last legs. No problem - worked perfectly. After doing something incredibly stupid, I hosed a chip on the colorDMD. Since there were other issues resulting from my moronic maneuver, I needed a temporary display for troubleshooting the Spider-Man pin and attempted to use the DMD from T2...and discovered that it didn't work...only got one or two lines. I don't recall the voltage measurements, but the manufacturers were different. Pins are all operational now, but the test was surprising since I had been under the impression that DMD's were all interchangeable.