Dig Dug repair guru?

JoeB1355

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Got any tips? I'm trying to understand the relationship between the 3 CPU's. My board keeps watchdogging and I can only get activity on CPU 1, how and when do other CPU's come into play?

pin 40-30 have activity on cpu 1 and on cpu2 and 3 nothing no hi or low dead. I tried all cpu's in slot 1 and they all have activity so I think the cpu's are good or at least not 100 % dead as they appear when in slot 2 and 3.

right now I thinking of pulling the 139 chip since roms and 2 and 3 never get selected only 0 and 4 get selected. We'll see if that gets me any further right it has a display with graphics an mostly the number 5 that flickers when the cpu is reset same display if I ground wddis just no flicker

the board was corroded and had some damage to about 10 or 11 traces I think I have all that fixed prior it was just graphics garbage no flicker. Kinda the way it acts with no CPUs installed

so after trace repair I think I'm a tiny bit further, but not too far I don't think!
 
I had a problem with a board starting and it drove me nuts (doesn't take much). The problem was a marginal z80 cpu. I replaced all 3 of the z80 cpu chips and game boots and plays but I get no sound when the player, sprite, is moving. The pumping sound is there and the fire breathing sound is there just music is missing.

Your case, I would replace the z80 cpu chips with some new z80a's or z80b's then I would verify the voltages and rom chips. Recheck all traces making certain they are connecting ONLY the the points they should. Use a logic probe after and look for floating pins on roms and addressing lines.

I currently have one of the original boards,latter revision, on the bench so if you need some pics of the traces that are damaged on your board let me know and I can take a med res. pic of the area for you.

Got any tips? I'm trying to understand the relationship between the 3 CPU's. My board keeps watchdogging and I can only get activity on CPU 1, how and when do other CPU's come into play?

pin 40-30 have activity on cpu 1 and on cpu2 and 3 nothing no hi or low dead. I tried all cpu's in slot 1 and they all have activity so I think the cpu's are good or at least not 100 % dead as they appear when in slot 2 and 3.

right now I thinking of pulling the 139 chip since roms and 2 and 3 never get selected only 0 and 4 get selected. We'll see if that gets me any further right it has a display with graphics an mostly the number 5 that flickers when the cpu is reset same display if I ground wddis just no flicker

the board was corroded and had some damage to about 10 or 11 traces I think I have all that fixed prior it was just graphics garbage no flicker. Kinda the way it acts with no CPUs installed

so after trace repair I think I'm a tiny bit further, but not too far I don't think!
 
I think I'll punt for now. I could replace a ton of sockets etc. Gonna wait until I find a good one and eventually fix this one as well when I can compare reading etc. I did swap the ls139 chip no fix same deal. I also tried new z80's and no luck.
 
I think I'll punt for now. I could replace a ton of sockets etc. Gonna wait until I find a good one and eventually fix this one as well when I can compare reading etc. I did swap the ls139 chip no fix same deal. I also tried new z80's and no luck.

I am in the same boat as you now. I have a working dig dug with the cpu chips in about the middle of the board and have one board I am working on that has all cpu chips on one side.

I had a bad 2114 ram chip It got extremely hot and burned my finger. I only replaced the one so I may have more bad.

I am looking into the addressing and decoding parts of the first priority cpu. There is also a 74ls128 chip I think that goes straight to the watch dog pin 26 of the cpu chip. There is several of the 139's and 367 all 74ls. The 32's right near the cpu is worth looking at as well. I have found a bad 74ls139 right near my 1st cpu chip.

What ver. board do you have?

You have to find out why the first cpu is not working first. That cpu chip does the primary testing ram and roms but if your board is doing what mine is doing, it is not even getting to the point where anything is being tested.

Since we are not seeing the ram ok that is probably where we need to start, after voltages, clock, nmi, and adress lines.
 
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I threw in the towel on the damaged board it was corroded all over as well. I end up getting 2 more board for a good price and 1 worked! the other kinda works -- no background but it plays. Eventually I get to it. I have one for my game though. The damaged one I think will just be parts now as I'm sure it would have always been problematic with the corrosion anyway.
 
I threw in the towel on the damaged board it was corroded all over as well. I end up getting 2 more board for a good price and 1 worked! the other kinda works -- no background but it plays. Eventually I get to it. I have one for my game though. The damaged one I think will just be parts now as I'm sure it would have always been problematic with the corrosion anyway.

I would like to look at the board. Can you post a pic. and are the cpu chips on one side or in the middle on the damaged board?
 
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