TSPP MPU board strange behaviour

[robm]

Went to look at a TSPP for someone today, and was getting random resets, locked imaged on the DMD, and at one stage, the text on the small TV DMD on mini playfield would scroll when the coin door was open, then lock still when you closed it. sometimes the blanking LED would flash on the power driver board. I swapped power driver boards with my known good one from LOTR and still had same symptoms. Often it would say balls were missing, and switches wouldn't register. Then if you hit the coin door buttons it would sometimes boot OK, then it would reset 10 secs later.

I ended up bringing all the boards (including display driver and DMD driver) as well as ribbon cables and put them in my LOTR at home, one by one they all worked fine until the last one i put in was the TSPP MPU board with only changing the LOTR game ROM (so RAM, sound roms are still TSPP) - and got very similar symptoms. It can't find balls in the trough, coin door opening makes strange behaviour (sometimes resets, other times locks DMD), so it is definetly something on the MPU. The 5V is 5.03 and 12 is 11.95, and they stay quite constant.

Any ideas where to look or what to look at replacing on the MPU?


Thanks

Rob

[Strangeways]

Check the board - top right hand corner - any battery leakage ?

Remove the CPU and check the socket. I had a recent whitestar board problem where the visible corrosion was confined to the RAM and CPU, but then found it had traveled to the video connector and associated chips.

[robm]

Found some minor acid on u213 and swapped chips and it worked for a while. Then I put all my original lotr boards back in my machine and the same problem cropped up. It seems bizarre as the 18v goes into the dmd power supply board but no 12v out. This happens with 2 different dmd power supply boards....

Anyway all too hard for me so posted then all to beaky this morning!