Quoted from 27dnast:
I had posted this in a separate thread...but am still looking for some brainstorming. My BSD has a ghost in the machine, so to speak:
Once every 40 games or so, if a ball hits the center or left target on the stand-up bank straight up the middle, the game will start randomly (and quickly) handing out rewards (such as a coffin ramp hit, a rat hole hit, video lane hit... sometimes the dungeon (upper left scoop) hit...). Then, just as quickly as it started, it stops and the game goes back to normal play.
I've had the glass off...can't get it to recreate. Put it in switch test and banged around... nothing. I've also looked under the play field...can't seem to find any loose wires or shorts.
Anyone have any thoughts?
Just wanted to update everyone on this... I solved the mystery. It turned out to be a faulty matrix chip (the ULN2803) which is located just below the batteries on the MPU board. After looking through all the switches on the playfield, checking diodes, loose wires, etc... I switched MPU boards with my TZ (changing ROMs, of course). The issue completely disappeared.
So, I ordered a new 80-cent ULN2803 chip from Pinbits... put it on the BSD MPU board and the game is back in business.
Subsequently, and totally unrelated, my DMD board crapped out. The power section needs rebuilding.
But, if anyone starts to see some strange behaviors (like I experienced) in their machine, keep that ULN2803 chip in the back of their mind. It could very well be the problem!
Special thanks to Gaz (over in Australia) and Chris Hibler for taking the time to think about this issue... their help was key and very appreciated!