What could cause text but no graphic in an arcade game? <spaceharrier/ pic link>

[Xphile]

posted a msg in r.g.v.a.c, and got only one reply, so I was hoping for a second opinion, and I didn't know where else to get one..:-(

I picked up a Space Harrier upright at an auction and everything seems to work great... It Powers up, Lights come on, sound and music happen, voice says "Enter the Fantasy Zone" (or something like that:-) and everything else seems to work properly.. (test mode shows all directionals on the flight stick work, all the buttons work, and the start button blinks when I add credits on the coin mechs.)

The Problem it has is there is Text on a white screened monitor, but no background. No people wearing jetpacks flying around, no monsters, no rocks...nothing. Just the text parts show up: Score, High Score, Credits, Lives Left...Anything Text ( including words on the test screens ) Shows up, but nothing else.

I can actually play the game ( flying blind :-) , so I know the game itself is working....I can watch the score go up (until I run into someone or something and die :-) I can shoot, (well, I can hear myself shoot, can't see it though..and I can't see if I hit anything...:-)  

It's a cool looking Cabinet, It would just be really neat to be able to get it going again..

I have some pictures of the symptoms at:
http://www.geocities.com/spaceharrier1985/

A link to a pic that really shows the problem is:
http://www.geocities.com/spaceharrier1985/sh_19_sm.jpg


If anyone has any ideas what I could try, I'd really appreciate it..

mike

[BobA]

Did you use the test screen to test all the parts of the board that you can?   Since you can see the tests it would be beneficial to test CPU, Memory and whatever other tests are available to you.  The Sega Space Harrier has a very complex video setup that allows different layers of video for text and sprites.  Since you can read text you have part of the video working so use whatever tests are available to see if they point to any problem areas.

Bob