Green Eyed invisible ghosts Pacman

massatari

massatari

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I'm punching a little above my weight on this repair but I'm going to throw myself into this.

Got a pacman board that was powering up ok but giving a solid red screen over the maze.


redscreen.jpg

Replaced the RAM @ 2D per a number of online resources and reseated all socketed IC's. Full disclosure I didn't have a clean desolder. I will not attempt removing IC's again without a better desoldering tool(I used a pump and wick). I had to repair a couple broken traces but I have used a meter to verify all traces are repaired and clean. the IC continuity checks correctly to everywhere and does not appear to be missing anything or be shorted anywhere that I can see.

SO... I am here. I have cleared up the red screen and I'm playing blind now. The ghosts have green eyes in maze. and pac is invisible. My question for the forum is for general advice. Do I keep trying to troubleshoot 2D and see if there was any other issue that I created or is this problem possibly somewhere else on the board?






Now
 

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You might have a problem with one of the ROMs and or ROM sockets. Have you tried reseating them to see if it helps?
 
kingdbag said:
You might have a problem with one of the ROMs and or ROM sockets. Have you tried reseating them to see if it helps?
Click to expand...
I did reseat but I'll try again and take another look. I actually have a new set of ROMs on the way. Come to think of it I have some spare ROMs as well I can play around with. Thanks for the suggestion
 
I would start by making sure to test continuity from/to all the pins at 2D. May need to check the other ram in 2A-C as well. Follow the schematics. Also check the color proms at 4A and 7F. Make sure they are seated properly and clean.
 
madrits said:
I would start by making sure to test continuity from/to all the pins at 2D. May need to check the other ram in 2A-C as well. Follow the schematics. Also check the color proms at 4A and 7F. Make sure they are seated properly and clean.
Click to expand...
I will revisit 2D and follow the schematic thanks for the pointers.
 
Reseating ram, same.. but I was just resoldering 2D and this is what I got. I'm convinced that I did something to this when I swapped out this IC, I really want to fix my mistake if it was me.. I got Pacman to come back. but now I have 2 colored ghosts in the maze red and blue with messed up eyes.
 

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M(red, red, cyan, cyan)
Ms Pacman's blue center in ribbon is gone. Monsters have cyan eyes with yellow pupils.
2C bad, removed, shorted p15 to p16, or p7 is high.
Signal from 3A p9 to 2C p15 high.
Signal from 2C p7 to 3D p6 high.
3A p9 short to p16.
 
madrits said:
Do you have a logic probe? check pins 7 and 15 on 2D and 2C
Click to expand...

Waiting on one to be delivered, This is definitely the farthest I've gone in repair so I'm getting tools along the way. I am also building a test rig out of an old Midway Transformer board and harness I have had hanging around so I dont have to test in the cabinet. I will report back after testing. Thank you for these replies.
 
If you get a good desoldering setup and you have tested your previous work on 2D then I would pull 2C next
 
madrits said:
If you get a good desoldering setup and you have tested your previous work on 2D then I would pull 2C next
Click to expand...

Thanks, I'm going to get in there with the logic probe. I have the chips to do 2A-2D. I really think 2D is good right now. Can you recommend to me a better desoldering setup? I have just been doing components and caps with my pump and braid with decent results. Not a beginner but I don't do this for a living so I really just need a good mid-level setup. I'd really like to pull all these chips and replace with sockets but I don't want to do it with the tools that I have.
 
A search on here will provide soooo much info on this subject. If you're only doing this occasionally then a cheap 45w desoldering iron with pump will meet your needs. https://www.parts-express.com/ecg-j-045-ds-45-watt-desoldering-iron--372-202

Just tin the tip and keep it clean. practice on something first. let it get real hot. If it doesnt suck out all the solder, then just resolder that pin and try again. Old solder can be a stickler.
 
madrits said:
A search on here will provide soooo much info on this subject. If you're only doing this occasionally then a cheap 45w desoldering iron with pump will meet your needs. https://www.parts-express.com/ecg-j-045-ds-45-watt-desoldering-iron--372-202

Just tin the tip and keep it clean. practice on something first. let it get real hot. If it doesnt suck out all the solder, then just resolder that pin and try again. Old solder can be a stickler.
Click to expand...

I got boned on this one by going off script. I had some old solder on the component side of the board that just was not coming out from the bottom side. I saw some videos of people desoldering from the component side and I thought I could pull it off with a braid but I was not as careful as I should have been and damaged some traces. I ended up doing some repair work that I'm not wild about but it came out ok. I saw some people using some really nice guns and I thought I'll never do this again the way I did it. Thank you again for all your help.
 
desoldering braid is useless on a board like this. The Hakko 301 is $250 but has a learning curve. Easy to damage boards if not careful.
 
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