Neo Geo 1 slot screen goes black after a few minutes

Kodos

Timid Neo Newbie
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May 23, 2022
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I have a 1 slot Neo Geo MVS that is starting to show its age. I initially had some screen issues with lost colors and blurred images that was attributed to caps on the CRT control board. I purchased the kit for a QNIC CGM-2500 and replaced all the caps including the filter cap.

After reinstalling the board everything worked fine and screen looked good so the caps seemed to have fixed that problem. A short while later the screen went black. Cycling power will restore screen for a period of time but it will eventually go black again. The system is booting and while black I can still hear the audio from the game.

I have searched this issue but nothing seems to match a rom actually booting and then the screen going black.

I'm looking for suggestions on what I should look at to diagnose this problem.
 

Neo Alec

Orochi Spam Riot
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If you have a Unibios installed, be aware that while in one of the Unibios menus the screen will go black automatically if nothing is pressed for some time. This is a screen saver, and the screen will come back after any button is pressed.
 

Kodos

Timid Neo Newbie
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May 23, 2022
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If you have a Unibios installed, be aware that while in one of the Unibios menus the screen will go black automatically if nothing is pressed for some time. This is a screen saver, and the screen will come back after any button is pressed.
It is original unmodified logic board and original SNK ROM. Magician Lord is loaded now but I have tried KoF 95 and King of the Monsters 2. I saw your post on the other forum. I'm new to the online Neo Geo community. I have lucked out that the cabinet has be working for over 25 years and now I need to learn how to refurb these machines.
 

BIG BEAR

SHOCKbox Developer,
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If you have another logic board you may want to swap it out so you can isolate the problem.
My thinking is your monitor is the culprit and not the board but again if you have any other jamma logic board you should use it and see what happens.
BB
 

Kodos

Timid Neo Newbie
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May 23, 2022
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If you have another logic board you may want to swap it out so you can isolate the problem.
My thinking is your monitor is the culprit and not the board but again if you have any other jamma logic board you should use it and see what happens.
BB
I don't have any additional spare parts to work with. I figure the likely candidate is the QNIC CGM-2500 that I removed and worked on but I had a friend with good soldering skills do the cap replacement and the board looked good prior to reinstalling it. It also fixed the screen problem I was having prior to the black screen.

Based on some research even though it probably won't fix the problem I can try cleaning the rom and rom slot and do the board cleaning I did for the monitor board just to remove all the dust. I also figure I can try booting without a cartridge and see if the monitor stays on longer or in diagnostic mode.
 
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BIG BEAR

SHOCKbox Developer,
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I don't have any additional spare parts to work with. I figure the likely candidate is the QNIC CGM-2500 that I removed and worked on but I had a friend with good soldering skills do the cap replacement and the board looked good prior to reinstalling it. It also fixed the screen problem I was having prior to the black screen.

Based on some research even though it probably won't fix the problem I can try cleaning the rom and rom slot and do the board cleaning I did for the monitor board just to remove all the dust. I also figure I can try booting without a cartridge and see if the monitor stays on longer or in diagnostic
I'm pretty positive there is no issue with your motherboard..
This reads like a problem with your ground or sync with monitor.
You never had to work on the mobo and the last part worked on(the monitor) is where the issue lies.
BB
 

Kodos

Timid Neo Newbie
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May 23, 2022
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I'm pretty positive there is no issue with your motherboard..
This reads like a problem with your ground or sync with monitor.
You never had to work on the mobo and the last part worked on(the monitor) is where the issue lies.
BB
Agreed that the thing I touched is the most likely candidate. Unless I can find something obvious like a lose connector or something I fear I'm going to need the help of someone who can test and service the board. Obviously my attempt to do that was incomplete. I'm not sure I want to buy additional boards of unkown condition to try just yet. May come to that eventually. My cabinet is a pain to work on in the back. It only has a small angled access panel above tube and one at the bottom. The big section behind the tube doesn't remove with screws. I'll open and and at least take some pictures in case someone asks for info I don't have. I have a feeling I have the very first generation one slot based on the pictures I have seen but I might as well confirm and take a look at the battery everyone posts about.
 

Xian Xi

JammaNationX,
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If it's playing blind then it isn't the board. Definitely start by checking the connection between the board and the monitor.
 

Kodos

Timid Neo Newbie
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May 23, 2022
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Updated info, I removed ROM and powered it up while timing it. Grid was on screen for 20 minutes then went black. I inserted ROM and went into diagnostic. Everything seemed to check out so I went back into game mode. I played for over 30 minutes with no issue so don't know if it is activity related or not. I went ahead and pulled the board out because the battery is toast but it doesn't seem to have effected nearby components. I'll clean the board up and all the connectors. I didn't notice erratic screen behavior when I touched the ROM cartridge. I'll check all the CRT connections when I reinsert the main board

IMG_4491.jpg.IMG_4489.jpg
 

Kodos

Timid Neo Newbie
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May 23, 2022
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I replaced the battery on the main board just to prevent future problems there and checked all the connections. I didn't really find anything. My main suspicions now is something heat related. I think the game board is ok so it it has to be something on the CRT side of things. It will run for a period of time and something must overheat. Once it cools it will work again. I am not sure what the time cycle is. I played it for an hour with no issue but I am confident it would have turned off at some point. I felt around looking for hot components. The heat sink on the QNIC CGM-2500 gets hot. I could put my hand on it for a few seconds but not keep it there. I am not sure what normal is.

IMG_4520.jpg
 
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