Pr3tty F1y
Beginner
I have an Atari Dig Dug board that's a bit rusty and crusty. The PCB looks fine but a lot of the DIP chips have corroded pins. When I initially got it, it wouldn't boot.
I've slowly been getting it back to operational order, but my troubleshooting skills are limited.
All of my ROM chips should be good (with the exception of the EAROM at 10G as I'm just not familiar with it and I was planning on leaving it be for the time being). All EPROM chips either tested good or I UV erased/reprogrammed the bad chips that were receptive to being UV erased. For the ones that were not able to be cleared, I used replacement 2732's and 2532's which all test fine now on my XGecu T56.
I replaced a SN74LS298N at 2H/J that was physically cracked (no idea what happened, nothing else around it looks damaged). I also reseated all of the socketed DIP chips on the board.
I replaced the RAM chip at 9M with a good TMM2016BP. I also socked the AM9149-55DC RAM chips at 4J and 3G as I thought that they may be bad, but when swapped out with replacements; they were not the issue. So I socked all 6 2114 RAM chips from 9J/K through 9E/F.
So my problem at the moment is that I have a short between ground and +5V that measures between 109-121 ohms on my multimeter for practically every chip/via on the board. I've read that I may be able to identify the shorting chip by it having a lower resistance the other chips, but I'm just not having any luck. Maybe it's my technique (i.e., should I be hitting the chip legs only or is it OK to touch the chip legs against where they're soldered to the board?). Either way, the symptom is really weird.
The board will still boot in this state, but ONLY if one of the 2114's are missing. I apparently did have one bad 2114 because swapping in any combination of the existing/replacement chips that I have all cause a horrible buzzing and the board doesn't boot at all. With all 2114 sockets populated with good chips, you get a corrupted cross-hatch grid that gray and moves in a slight jittery wave (i.e., I've seen similar "wavy" graphics that look like they're being combed with bad RAM chips on other boards). However, if I remove any one of the 6 2114 RAM chips, I get to the scrambled tile boot up sequence and there is no buzzing sound. Of course the board gives a RAM error for whatever slot is missing (from page 2-3 of the manual here: https://www.arcade-museum.com/manuals-videogames/D/DigDug.pdf) but it actually looks like the boot up sequence of a working board.
So there is something about populating all of the 2114 slots with good RAM chips that is causing the ground fault to just fizzle everything out (at least that's my working assumption). I'm also thinking that the ground fault may have been what killed one of the RAM chips so I've only been powering on the board briefly to test.
Has anyone else seen anything like this or have any thoughts? I'd be happy to hear from you because it seems like this thing is so close to booting. I'm just not quite sure where to go from here.
I've slowly been getting it back to operational order, but my troubleshooting skills are limited.
All of my ROM chips should be good (with the exception of the EAROM at 10G as I'm just not familiar with it and I was planning on leaving it be for the time being). All EPROM chips either tested good or I UV erased/reprogrammed the bad chips that were receptive to being UV erased. For the ones that were not able to be cleared, I used replacement 2732's and 2532's which all test fine now on my XGecu T56.
I replaced a SN74LS298N at 2H/J that was physically cracked (no idea what happened, nothing else around it looks damaged). I also reseated all of the socketed DIP chips on the board.
I replaced the RAM chip at 9M with a good TMM2016BP. I also socked the AM9149-55DC RAM chips at 4J and 3G as I thought that they may be bad, but when swapped out with replacements; they were not the issue. So I socked all 6 2114 RAM chips from 9J/K through 9E/F.
So my problem at the moment is that I have a short between ground and +5V that measures between 109-121 ohms on my multimeter for practically every chip/via on the board. I've read that I may be able to identify the shorting chip by it having a lower resistance the other chips, but I'm just not having any luck. Maybe it's my technique (i.e., should I be hitting the chip legs only or is it OK to touch the chip legs against where they're soldered to the board?). Either way, the symptom is really weird.
The board will still boot in this state, but ONLY if one of the 2114's are missing. I apparently did have one bad 2114 because swapping in any combination of the existing/replacement chips that I have all cause a horrible buzzing and the board doesn't boot at all. With all 2114 sockets populated with good chips, you get a corrupted cross-hatch grid that gray and moves in a slight jittery wave (i.e., I've seen similar "wavy" graphics that look like they're being combed with bad RAM chips on other boards). However, if I remove any one of the 6 2114 RAM chips, I get to the scrambled tile boot up sequence and there is no buzzing sound. Of course the board gives a RAM error for whatever slot is missing (from page 2-3 of the manual here: https://www.arcade-museum.com/manuals-videogames/D/DigDug.pdf) but it actually looks like the boot up sequence of a working board.
So there is something about populating all of the 2114 slots with good RAM chips that is causing the ground fault to just fizzle everything out (at least that's my working assumption). I'm also thinking that the ground fault may have been what killed one of the RAM chips so I've only been powering on the board briefly to test.
Has anyone else seen anything like this or have any thoughts? I'd be happy to hear from you because it seems like this thing is so close to booting. I'm just not quite sure where to go from here.
