Sega Star Trek problem, need help!

I purchased a Sega Star Trek convert-a-cab about 18 months ago (as non-working). It's been sitting in my game room since then waiting for me to get to it. I knew the monitor was dead so I worked on that first starting just last weekend. I just recently completed rebuilding the GO8 monitor and it is working great now.

If anyone wants to know, the 4x TO-3 power transistors are new MJ21196G. I list these on my site as replacements for the 2N6259 here...
http://www.biltronix.com/arcade_electcomp_01.html#transistor_subs_2n6259

The monitor also had a shorted Q603, that's a MPSU10. I replaced it with a MPSW42G which is a cheap yet superior part in a tall TO-92 case. It is available at Digikey. With a small press-on heatsink (Digikey HS251-ND), it works great. Similarly, the MPSU60 can be replaced by the modern MPSW92G (Digikey# MPSW92R something, I'll post it on my site later).

Before I started with the monitor, the game was playing blind with sound. After I put the monitor back in, it looked great and was playing great. About 10 minutes into it, there was a pop sound and the game reset. There is no longer any audio at all and the graphics are a bit mixed up and the image appears to be rotated 45 degrees clockwise.

The power supply output is exactly +5.05V. Resetting the game doesn't change anything. I have reseated all socketed chips and verified all 24x 2716 chips on the eprom board. I had some spare boards sitting in my basement so I swapped them out one at a time. Most of them didn't work but I can say at least that the XY-control board is fine. I'm also doing this troubleshooting with the speech and sound boards pulled out. I read somewhere that the game should run without them. Pulling these two boards did not change the behavior of the game at all.

Does anyone have any suggestions? Any help is appreciated.

William Boucher

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Received on Tue Aug 18 23:25:06 2009