The Simpsons missing characters stage 3

tnglc79

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I have a dedicated Simpsons which is all original. Had been in storage for 15 years because the power supply went out. I replaced the power supply and the game plays great, but...

In stage 3 the intro characters show, but once gameplay starts there is only the shadows on the ground. This remains the same until close to the end of the graveyard scene, then everything comes back. You can walk across the threshold one way and they disappear, then back the other way and they come back. The Scene in Moe's does it for about six inches of the whole scene as well. No other part of the game seems to have any other issues.

So far, checked voltage, cleaned EPROMS and sockets. Checked board for small cracks (had never been removed prior) Cleaned edge connector and harness. While cleaning the EPROMs, I verified them (mask roms) against a known good dump and they all checked good.

Just ordered some 27c010 eproms to write new ones (plus I am going to burn the freeplay rom) just in case there is some bad code the verification is not reading.

Is there anything else I should look for in the mean time to see if the problem is elsewhere?
 
Man issues like this suuuuuck because 99% chance it's going to be a leg on a surface mount custom chip or fpga or whatever the big square chips are called. Very hard to troubleshoot and then you have to have someone skilled enough to make the repair if a chip has to be replaced. To make it even worse, the board 'almost' works, so it's teasing you. To make it worse, on top of that, it only screws up 15 minutes into the game.... so you can't even troubleshoot it quickly, if you find someone that can troubleshoot it.
 
Phil- I did run all system tests and everything shows okay. Of course in the past I have learned that this means nothing in some cases.

Lyons- Sounds like you have had some experience in this or something like it. Fortunately I do have the ability to do the repairs, I also have the equipment to troubleshoot, but on the other hand I am not too good with following logic, maybe this means it is time to learn to use the o-scope right.......Definitely not a board I want just mostly working.
 
Okay, so I haven't looked at the board again, but I did just watch a playthrough on the game and realized I am missing more sprites than just those. On the first board a couple of the background sprites (the kid in the arcade being one) are not there until they come out of the background. On the second board the bear is missing until he busts out of the cage, etc. So I guess tomorrow I will have a look and see if there is any obvious damage to the board then decide where to go from there. Oh the joy. Was hoping this would be a simple fix.
 
Okay, so I haven't looked at the board again, but I did just watch a playthrough on the game and realized I am missing more sprites than just those. On the first board a couple of the background sprites (the kid in the arcade being one) are not there until they come out of the background. On the second board the bear is missing until he busts out of the cage, etc. So I guess tomorrow I will have a look and see if there is any obvious damage to the board then decide where to go from there. Oh the joy. Was hoping this would be a simple fix.

Can you shoot a video of the problem? I have a couple of theories.
 
Okay, so I haven't looked at the board again, but I did just watch a playthrough on the game and realized I am missing more sprites than just those. On the first board a couple of the background sprites (the kid in the arcade being one) are not there until they come out of the background. On the second board the bear is missing until he busts out of the cage, etc. So I guess tomorrow I will have a look and see if there is any obvious damage to the board then decide where to go from there. Oh the joy. Was hoping this would be a simple fix.

Take a look at this, it may be a good start

http://www.jammarcade.net/konami-simpsons-repair/

paris
 
Okay, finally got a chance to burn the new EPROMS and add the freeplay rom. Started up with test button held in. Everything checked out okay. Freeplay mod works fine, but the sprite issue persists as I thought it would. Just took a video. Sorry for the crap one hand play one hand record but it is the best I can do right now.

Shows the tez cup guys missing in back ground, then appearing in playfield as well as the bear. The next little section shows Level 3 starting and then everything except shaodws disappearing all the way until they come back. Then a little walking back and forth to show how the characters are there then gone. Odd crap..... The youtube link is: https://www.youtube.com/watch?v=tuWdcyffW7Y


I would really like to fix this issue as I will be keeping the game at the house. It will never make me money, so I would like to keep the repair cost at a minimum. Already have more in this game than anything else I own, but well worth it in my book as is, just wish it was perfect.
 
This looks like it could be a priority/ordering issue. The IC that determines which layer (e.g. sprites or backgrounds) should be visible for each pixel is the 053251.

The priority code from the sprite chip (053247) arrives at the PR10-5 pins (see the schematics but note that only a small subsection of the video hardware is included). Assuming the 053251 is ok, I'd work backwards from there.
 
This looks like it could be a priority/ordering issue. The IC that determines which layer (e.g. sprites or backgrounds) should be visible for each pixel is the 053251.

The priority code from the sprite chip (053247) arrives at the PR10-5 pins (see the schematics but note that only a small subsection of the video hardware is included). Assuming the 053251 is ok, I'd work backwards from there.

Just did some testing. and learned this: The missing sprites are only when pin 29 of the 053251 is high. If I ground the pin via jumper the missing background sprites become visible, but also sort of in front of the foreground. Board 3 is perfect though. I will post some pictures of what the grounded pin 29 is doing or maybe another video.

So now we know something is up here. As for me I have no f***ing clue at this point. It's 3:30 in the morning and I should have been asleep by now, lol.
 
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Okay, so in a last ditch effort I desoldered, cleaned the pads and surrounding pcb and resoldered legs 27, 28, and 29 on the 053251. (NO FUN BTW- definitely easier to replace a hole ic than do this). The game is up and running 100%. While I had the legs desoldered and bent out I noticed pin 29 (if memory serves me correctly) had a through hole connection, which at the time had no continuity. I cannot verify if it had it before or not, but it does now. I know this answer still seems like a crap shoot for someone who may have the same problem in the future, but in all honesty, I really didn't think it would work or I would have taken notes as to exactly what I did.

I do believe it was simply a faulty connection in the through hole passage, but I cannot verify 100% and since it is working, I don't plan on experimenting to see if that was the true culprit.

I would also like to extend a huge thanks to all of you for the ideas and help, Definitely Phil Bennett for pointing me to the 053251. Saved me a few hours of going from the outputs backwards.
 
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