Hey. I’ve been spending a lot of time the past week or so working on the Vidiot board from my Baby Pac-Man. The last thing I mentioned here is that I was getting 8 flashes from it on boot. You should get 10 when everything is working properly. 8 usually indicates that the TMS9928 chip in U16 is bad. I ordered (2) NOS replacements from Jeff at Classic-Arcades.com. I don’t think they are listed on his site, but he mentioned he had them in the RGP newsgroup. I figured it would be good to order an extra because they are hard to come by.

I waited patiently for the chips to arrive, and popped the replacement in. Unfortunately, it still had the same problem. :(

I’m suspecting the crystal that controls the timing for U16 might be bad. Someone mentioned they had that problem (in the RGVAC newsgroup?). I don’t have another crystal, so I ordered some. I’m hoping they’ll be in tomorrow. In the meantime, I tested just about everything I could on the board. I won’t bore you with all the details, but let’s just say I spent a ridiculous amount of time working on it this past weekend. I worked on it most of the day Saturday, up until about 4AM Sunday. Then, I slept a few hours and went back at it again. (Yes, I’m insane).

One of the things I noticed is that there was a capacitor (C87) that was broken off the board:

IMG_3477

Seeing this made me excited, because it was obviously wrong. Changing it didn’t do squat to fix the problem with U16, but at least its replaced now.

I figured I would replace the rest of the old sockets with machine pin sockets in case one of them was making a crappy connection. I started with U8, because that’s the chip that is reporting that U16 is bad. By the time I got to working on this, I had lost a lot of sleep. I’m not sure if that factored in or not, but I really screwed up a trace. I usually cut off the old sockets, exposing the pins. Then, I grab each pin with pliers, heating the solder until it melts, and the pin pulls right out. On one pin, the trace came right up with the pin:

IMG_3479_commented

This is the first time I’ve ever lifted a trace like that…I hope it’s the last! I repaired it on the underside with a 24 gauge solid core jumper:

IMG_3484

I told you I wouldn’t bore you with all the details, but I guess I lied. I’ve been keeping a list of everything I’ve done in notepad on this board…here it is in excruciating detail:

  1. All voltages on board OK
  2. Changed socket for U16 and put new chip in….still N/G
  3. Every pin on U16 is connected to where it should be, via continuity test
  4. C73 is OK
  5. C62 & C63 seem OK (they surround the Y2 crystal)
  6. Tried to get a pulse on crystal Y2 via logic probe and couldn’t…not sure if it should pulse or not.
  7. Changed C54 - no effect
  8. Diodes are OK: CR1, CR2, CR3
  9. C87 was broken off…replaced it  - didn’t fix problem
  10. Pulled all socketed chips, cleaned, reseated
  11. Swapped 2114 RAMs in U13 and U14. No change…put old ones back.
  12. Changed C92
  13. Changed C107
  14. Changed C109
  15. Tried a 10mHz crystal from Kangaroo….N/G
  16. Changed C62 & C63…N/G damn it
  17. Changed socket for U8.

I’ll let you know what happens when I put the new crystal in…