Yesterday, I visited the person who was very kind enough to give me assistance. He had all the gear, oscilloscope, test system, chip readers, etc.
Very interesting experience as we weren't able to rectify but things that he did made the situation better...then worse throughout the day. He still has the board as he wanted to think it over. He suspects the Red 8 custom which is going to be dead board basically. I'll try to summarise things done (and results) to see what you guys might recommend trying further.
1) He checked signals (by putting signal through or is it shorting?) of the Yellow 3, Yellow 4, Blue, chips to the right of Green 1, above Yellow 4. He did it by checking these against their respective data sheets. Some weird things were found like no signal coming from some legs of the bottom Yellow 3 chip but they didn't look like they were going anywhere.
2) Bottom 3 chips of Yellow 3 removed, checked in chip reader to be ok. Turned on the board and problem sprites were missing from the screen (ie. nothing was there) so he was confident issue was around that area. Chips put back in.
3) Chip above Yellow 4 next to the C on the PCB, removed, checked in chip reader, replaced with another chip.
4) Checking signals (by putting signal through or is it shorting?) regularly froze the board.
5) Took out ROMs 5 and 6 and checked against MAME codes. I've suggested maybe to check 1H, 2H, 3H and 4H ROMs since they are the program ROMs?
6) He sprayed freezing solution on Red 8 and other chips to see if any erratic behaviour resulted. It did when it was sprayed on Red 8. Situation got worse than original.
7) Putting signals through the chips in Yellow 3 would affect the problems sprites as in it would make it better or worse. But the chips were ok.
He used non conductive material to to press the legs of the Red 8 chip to see if it affected it. It didn't.
9) He did much more but I couldn't understand or keep up. He was so kind in spending over 5 hours on it. Did other stuff like checking the connections between the Yellow 3 chip legs and the Red 8 chip via multimeter.
10) Why would putting signals through Yellow 4 make the board repeatedly freeze when they're sprite related? I would have thought this would have happened if it was done to the chips in Blue?
11) Apart from asking him to check the 1H, 2H, 3H and 4H Program Code ROMs, I stiill need to let him know I thought of something overnight. I noticed a rattle noise, I shook the board and heard it coming from around the area of the 1H, 2H, 3H and 4H CPU Program ROMs. When I took out the chips, I tried shaking and the noises disappeared. When I put the ROMs back in, the noise reappeared. Not sure if it means anyything.
Thanks for any help or suggestions!!!
Cheers,
Michael.
