Worked with some friends on the HD's today.
Because both HD's had monitor issues (one was happily burning away it's HVT, the other has bad sync problems) we first hooked up a VGA monitor using one of those cheap Chinese CGA/EGA to VGA converter boards. Excellent little things, worth every cent !
We got picture with self test screens OK on it. Although it chopped off the left-most part of the picture, it was definitely workable. (Probably could have fixed it if we had tinkered with the settings, but we decided to spend the time on getting some HD boards running.
We first ran the tests and sure enough 3 of the VRAMs were indicated as bad. We then piggybacked all three and ran the test again, to our own slight amazement, we were left with only one bad ram, so the other two were successfully piggy-backed.
For the third one we assumed there had to be a short in that one, preventing the piggy backed RAM to work, so with snapped out the body of the old IC and then piggy-backed the new one again, and we had a 100% success !! All VRAMs working !
Not this HD still had some sound problems indicated which we will need to investigate further, but at least we could start up the game, see attract mode running fine, credit it and start a game by turning the key. The gas-pedal didn't seem to work though as the car never moved from it's spot. The steering wheel does weird things to, but that's all for later.
The 2nd HD had more problems on the PCB's. It also had four VRAMs indicated as bad. Again, the piggy-back trick helped and again we had to snap off one body to get it to pass the tests.
However, this set also gave errors on the ADP board. I made a picture:
All the red one's are supposedly dead RAMs.
However this type of RAM seems completely unfamiliar to me.
On the chip it says: hm3-65768m-5
In the schematics (From Jed Margolin) it says that these are 8168D45 RAMs.
Any idea where to get these or what chips are equivalent ?