Sega 16b green scrolling screen and locks up.

aapuzzo

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I have a spare parts board if needed. Where should I look first for fixing a Sega 16b with known good rom board that has a scrolling green screen that locks up? If I am fast I can hear hear the game start with music but it glitches in a loop. I think I was able to get into test 1 time but haven't been able to repeat. Attached is a screenshot. I validated continuity on all rom board pins to main board. The rom board is ESWAT. I tried a working Shinobi rom board and that one does nothing.
 

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I have a spare parts board if needed. Where should I look first for fixing a Sega 16b with known good rom board that has a scrolling green screen that locks up? If I am fast I can hear hear the game start with music but it glitches in a loop. I think I was able to get into test 1 time but haven't been able to repeat. Attached is a screenshot. I validated continuity on all rom board pins to main board. The rom board is ESWAT. I tried a working Shinobi rom board and that one does nothing.
I have now left it off a few hours and it seems to have changed to red. I can tell I am getting into test because I can hear the sound test running. I'm thinking I have bad memory somewhere but am open to suggestions. Which memory would I want to replace first? I am pretty sure I have a ton of these memory chips because I think they are the same ones the NES uses.
 

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I made some progress. I replaced the LS374 chip at J16 because the picture distorted when I ran my fingers over the pins with it powered on. I then probed the pins and found the output pins were dead even though the chip was enabled and shouldn't be in the 3rd state. Now the picture is still red and locks up a few seconds when trying to start the game but the test mode is at least readable in red. Screenshot attached. Now it says I have memory errors at H13, J13, H15, H16. I tried piggy backing memory chips on the 2 6116 chips and it didn't make a difference. I can socket and swap all of these chips out but should I look at something else first? The fact the J16 chip was bad means more could be fried but I'm hoping other with experience may have more insight on what I should replace first. I attached the schematic below. I have a donor badly corroded traces board for parts and can replace everything I just hope it's not the custom chip because that wouldn't be fun. Since the rom board sits on top it is very hard to probe.

Memoryerror.jpg
Screenshot 2025-05-26 134613.jpgScreenshot 2025-05-26 134613.jpg
 
Now I have swapped all the memory chips an am at a loss. I could swap the custom chip.
 
I'd guess that you don't have all that bad ram and something else in that circuit is failing and stopping the test from verifying the ram properly.

Look to see what is coming between all those.
 
I'd guess that you don't have all that bad ram and something else in that circuit is failing and stopping the test from verifying the ram properly.

Look to see what is coming between all those.

I socketed and swapped J15 now too. I hate to say it but it could be the custom chip. I'm trying to see if I can cleanly remove it from my donor board. Do you see any other chip that can cause all 4 of those ram chips to fail? My soldering skills are far better than my troubleshooting skills.
 
I socketed and swapped J15 now too. I hate to say it but it could be the custom chip. I'm trying to see if I can cleanly remove it from my donor board. Do you see any other chip that can cause all 4 of those ram chips to fail? My soldering skills are far better than my troubleshooting skills.
Follow schematics and see what may be common. I'm in warehouse today organizing so I can't pull up anything.
 
Follow schematics and see what may be common. I'm in warehouse today organizing so I can't pull up anything.
I made progress. All of the memory tests now pass. There were 2 more bad LS374 chips at H12 and G12. Each one restored 2 of of the 4 bad memory tests. The colors are still all corrupted and I have a random scrolling garbage pattern going through the screen but the game now plays and doesn't lock up. What part of the sega system 16b affects the colors?
 

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Color is fixed. I have to be getting close now. Wow this isn't a simple repair but I am learning a lot. The HC273 logic chips located at J11 and J12 were bad. Now all I am left with is no sprites and scrolling garbage through the screen which is probably related to the missing sprites. I think If I fix this now that will be the last problem. I'm probably going to call it a night. If somebody knows the chips related to the sprites that would be a big help. I think it has to be a bad logic chips because I already tried piggy backing all the memory chips with no change.

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Scrutinize the daughter board next. Looks for bad traces or sockets and verify all roms if you haven't yet.
The rom board is definitely good. I have about 5 working SEGA System 16b sets and this one was tested. I removed the working ESWAT ROM board to make a Cotton conversion. I was trying to repair a broken SEGA 16b main board so I can move Cotton to this one and restore the matching ESWAT set. I have also tested continuity between all pins of the 4x 50 pin connectors.
 
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Great news on getting the board working this far! With testing the LS374 IC's, are you using a logic probe to test the inputs and outputs for each IC? I have a board with similar issue which I've not had any time to work on, but once I do I'll check the LS ICs first up based on your experience above
 
Great news on getting the board working this far! With testing the LS374 IC's, are you using a logic probe to test the inputs and outputs for each IC? I have a board with similar issue which I've not had any time to work on, but once I do I'll check the LS ICs first up based on your experience above
I used a combination of touching chips while powered on looking for screen output changes, a logic probe, and piggy backing identical chips on top of others in the circuit I am troubleshooting. I think what I will try next is to run the board with one or 2 eproms removed at a time. If I remember correctly from a Golden Ax board I had with corrupted sprites which ended up being a bad memory chi[ when I found the correct circuit removing the Eprom made the corruption go away. Granted the sprites still weren't present but it at least pointed me in the right direction. This board is a little difficult to probe because the area I am working on is under the rom board.
 
List pics of the board also.
Here is a picture of the boards as requested. The Red circle represents everything I added sockets to.

- The chip marked in Yellow at J16 fixed some text and made it so I can read the diagnostics screen.
- The orange marked chips at G12, H12 both fixed the memory errors. Each one restored 2 of the 4 failures.
- The blue marked chips at J11 & J12 restored the colors.

If I was a gambling man I would probably start randomly piggybacking chips really close to those since all of the failures are near each other.

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I'm not having any luck at all fixing the sprites. There are definitely small pieces of sprites scrolling through the screen. I have now piggy backed almost every memory and ls chip with no impact on the output. I may have to just pull the ram but am open to suggestions.
 
Now I tried socketing all the chips circled in purple and swapping them with no difference. However if I test the game without them installed the corrupted scrolling sprites completely disappear so the issue must be somewhere with this. With my Golden Axe set these were bad and caused something similar. I'm starting to run out of ideas.


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I have now socketed and replaced all the chips that I think are part of the sprite circuit besides the custom chip 315-5196 with no luck. Testing the board without some of the LS chips or the memory chips H5 & H6 remove all the sprite artifacts also. I can try swapping the custom chip with another but I think I have a good chance of breaking it while trying to remove it. I don't want to do that unless it is really the last thing I can do. As said I am 100% sure the rom board is good. Screenshots of the 16b board and schematic I think is the entire sprite circuit below. A red circle has been placed around all the chips from the below schematic that I have replaced. I'm now going to try testing all the continuity between these points but I have already tested anything that could possibly look like a scratched trace. I haven't found any not visible corrosion on this board so far. If the consensus is to swap the custom chip would a better tool increase my odds? I have a Hakko FR-301 disordering gun, Hot air gun, and have been using low temp solder. If there is anything else that would increase my chances of success within reason I'll buy it. At this point it's not about the money, I just want to see if I can fix it and learn. Are their any chips outside of what is in the below schematic that can cause these symptoms of corrupted scrolling sprites besides connectivity to the ROM board?? I have fixed so many other problems on this thing I don't want to just give up.
Screenshot 2025-05-28 111351.jpg20250528_110334.jpg
 
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Game over I fixed it. I literally started checking every trace on the board and found 2 bad traces. The first one going from the GAL to the custom chip which DIDN"T make any difference with this game. I I was thrilled only to find out it didn't do anything and then I eye balled another on the top of the board in the photo which restored all sprites. testing the traces to the custom chip was the biggest PITA I ever did. What I did was hook my continuity tester to a piece of aluminum foil and apply pressure until I heard a tone which isn't easy because you get many false positives. If I couldn't' find it I tried with a known good 16b board and tested the actually pins on my bad one. I'll later clean up the board add some hot glue and photo resist.


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