i86time
Well-known member
I'm working on a spare GORF set and need some help. The first screen after boot (scores/text, 1/2 player ships, etc.) displays normally and the first level screen is mostly normal; the only issue is the shield is solid white and not sparkling. However all subsequent screens are missing any yellow, displaying only dark red or blue, are missing stars and do not show sparkling (shields/flag ship reactor). Using my good set, I narrowed it down to the game board (bad board in good set has issues while good board in spare set does not have issues). Using the same method I tested the two custom chips and they are fine.
I found a short on the board which I tracked down to a bad 74LS74 @ U14 and replaced it but it had no effect. Trying to diagnose the yellow, I tested Q6, Q7 & Q8 which all tested fine, but I went ahead and switched their positions which also had no effect. I then went ahead and switched out U20, a 74LS257, which feeds the VIDEO signal, again without any improvement. Since I wasn't getting anywhere with the yellow, I decided to move on to the stars/sparkle.
Looking at the schematic, the only chips I see dealing with the sparkle/stars are U5, 74LS153, and U6, MC10499/CD4099, which I replaced again without improvement. Since I didn't have any new CD4099 or 74LS257 I used pulls from my boards, but I know at least the 4099 is good as I put it back in the main GORF and it plays fine.
So, I'm open to ideas.
I found a short on the board which I tracked down to a bad 74LS74 @ U14 and replaced it but it had no effect. Trying to diagnose the yellow, I tested Q6, Q7 & Q8 which all tested fine, but I went ahead and switched their positions which also had no effect. I then went ahead and switched out U20, a 74LS257, which feeds the VIDEO signal, again without any improvement. Since I wasn't getting anywhere with the yellow, I decided to move on to the stars/sparkle.
Looking at the schematic, the only chips I see dealing with the sparkle/stars are U5, 74LS153, and U6, MC10499/CD4099, which I replaced again without improvement. Since I didn't have any new CD4099 or 74LS257 I used pulls from my boards, but I know at least the 4099 is good as I put it back in the main GORF and it plays fine.
So, I'm open to ideas.
