UMK3 - PIC Chip Bad error, but U64 is actually fine

dukesilverfan

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I picked up a UMK3 that had 5 ROMs that would show red on the boot sequence, then it would reset. I burned new ROMs and was able to see the rest of the boot sequence. All of the RAMs, the game ROMs, the sound ROMs, U33, U59, U63, U54, U49 - all green. The final part of the sequence gets to the U64 security chip, and that shows red with an error of "PIC Chip Bad, press any button".

I swapped a known working U64 in and it gave the same error. I then put the original U64 in a known working game, and it worked fine.

Visual inspection doesn't show any corroded sockets, no touching legs on the back side, and no trace damage.

Do U47, U45, or U35 have anything to do with the processing of U64? I am trying to find which area to poke around at next. Every search comes up with people replacing an actual faulty U64, but that isn't the case here.
 
It looks like U56 and U70 both communicate with U64 on this version of the Wolf board (no U55). I'll probe around those in the meantime, unless there is a smoking gun that I'm missing.
 
Still no luck, but I ruled out a few things:
  • I swapped both revision roms, as well as the U64 security chip from a working board - no change.
  • I swapped out each of the PLCC, one at a time - no change.
  • I looked over the bottom of the board for any touching legs or damage of any kind - found nothing.
  • I set all of the dip switches to the factory default settings of off - no change.
  • I changed the CMOS battery out - no change.
Each boot I am getting this exact same sequence, followed by the game getting stuck on the revision screen right before the serial number appears, and then the system reboots.
bad-pic.jpg
 
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