Re: Sega Star Trek problem, need help!

Thanks, I appreciate the advice. I did do the ground mod before there were any problems. The monitor is working fine now after the rebuild. I never powered the monitor up before working on it. I read all of the available faqs before proceding with anything. The game boards were still working a week ago but now have a problem, probably something minor since it still plays. Measuring voltages at the boards is difficult since the boards are all inside that box and I have no extender so I haven't done that yet. I know that I need to do that since there may be a bad power contact somewhere that is dropping voltage. I'm not yet using a switcher but the linear supply is working very well.

William Boucher
  ----- Original Message -----
  From: John Robertson
  To: vectorlist@vectorlist.org
  Sent: Wednesday, August 19, 2009 1:04 AM
  Subject: Re: VECTOR: Sega Star Trek problem, need help!

  William Boucher wrote:
    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
  Hi William,

  Have you done the absolutely essential ground/common upgrades? Do a search for "flameproofing Sega XY games" (GO-8 monitors).

  The original Sega power supply had a serious problem where the ground/common pin would bake and lose conductivity between the monitor and the logic ground reference - leading to exploding driver transistors on the monitor.

  The cure is to replace the original power supply with a modern video game switching power supply and to make CERTAIN that the common/ground wires between the monitor, logic board and power supply are well and truly connected.

  If that was not done it could have easily caused your problems.

  I wish I had some pictures of the older SEGA XY games we saved by doing this modification, however they are all in customers houses with nary a one having any trouble after ten or more years...

  John :-#)#

-- 
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Call (604)872-5757 or Fax 872-2010 (Pinballs, Jukes, VideoGames)
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