X
xenon325i
Playing my FT I got a few random resets from time to time. Naturally, I looked at the usual suspects but the +5V on the CPU was good with virtually no ripple (measured with oscilloscope).
Playing a few more games other oddities happened: during the game the credits would occasionally increase and the volume went up and down of its own accord. I left it for a while to think about it and then it occurred to me that what was happening was that the service buttons were being "pressed" at random, including service credits, volume and, of course, reset.
I turned the game on again and now none of the service buttons worked at all, which kind of confirmed my theory that I was in the right area.
For none of the buttons to be working at all following sporadic operation you'd guess at a wiring issue from the coin interface board to J207 on the CPU board but reseating had no effect. (game was working OK in all other aspects).
The schematics suggested that U16 and U17 (LM339s) were doing the bulk of the work for the dedicated inputs but how likely would they both be to fail at the same time?
Further investigation revealed no +12v on pin 3 on either of these devices. Having pulled the CPU board pin 3 to U16 comes from the infamous U20 and U17 is supplied from U16. There was no continuity between U16 and U20 and looking through a magnifying glass it looked like the track had lifted for no good reason.
I supplied pin 3 of U16 using a wire link directly from the +12v header and now all is well again.
Odd one, that.
Playing a few more games other oddities happened: during the game the credits would occasionally increase and the volume went up and down of its own accord. I left it for a while to think about it and then it occurred to me that what was happening was that the service buttons were being "pressed" at random, including service credits, volume and, of course, reset.
I turned the game on again and now none of the service buttons worked at all, which kind of confirmed my theory that I was in the right area.
For none of the buttons to be working at all following sporadic operation you'd guess at a wiring issue from the coin interface board to J207 on the CPU board but reseating had no effect. (game was working OK in all other aspects).
The schematics suggested that U16 and U17 (LM339s) were doing the bulk of the work for the dedicated inputs but how likely would they both be to fail at the same time?
Further investigation revealed no +12v on pin 3 on either of these devices. Having pulled the CPU board pin 3 to U16 comes from the infamous U20 and U17 is supplied from U16. There was no continuity between U16 and U20 and looking through a magnifying glass it looked like the track had lifted for no good reason.
I supplied pin 3 of U16 using a wire link directly from the +12v header and now all is well again.
Odd one, that.
