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MudGuts83

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Hey all.

I recently picked up an Irem M92 Major Title 2. I bought it knowing there was a graphics issue. I am looking to repair it if it is within my comfort/skill level.

When in the test mode going through the red, green, blue screens these graphic glitches are most prominent. When certain graphics in-game are overlaid - they cover these graphic glitches.

I have re-seated several but not all socketed chips. I will be buying a cap kit to replace the ELNA capacitors.

Watching a few repair videos, I did press down on a the qfp chips to see if they might have been the problem - and that doesn't seem to be the case.

I do have a logic probe on order. Any helpful recommendations/direction is appreciated.
 

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I did compare a few of the roms against Mame. IC 34 for majtitl2b only gives me a 99 percent match with a few bytes being off. Guess I could buy some eproms and burn a new one.
 
Taking out IC34 doesn't get me past the garbled picture before the ram rom screen. But, I'm pretty sure I'm still seeing dots where they had lined up prior.

I took out the IC above it, IC33. In the rom/ram test it pauses on the report saying "something something NG". The next screen, the one that tells me the adapter or whatever that was used for major title 2 isn't hooked up is the first obvious screen where the pixels are obvious.
 
Definitely start by replacing the ROM at IC34. According to MAME, that ROM holds a portion of the code for the main CPU. A few bytes being off could definitely cause the issue you’re seeing. You’ll want to use a 27C020 EPROM.

Garbled graphics and flashing colors at startup is normal - that’s the board running the diagnostic checks.

Unfortunatley there aren’t any M92 schematics out there that I’ve ever been able to find. MAME is always helpful for figuring out which ROMs do what.

914EB1B6-382B-400A-B34D-7D0C2F32E2D3.jpeg
 
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I appreciate all the replies. I'll look to put in a buyicnow order this coming week.
 
I finally got around to recapping the brown Elna caps. I also replaced a few damaged resistors. No change. I also programmed and replaced the one IC I found that had not matched the .bin in Mame. No luck.

I have a few programmer adapter boards on their way. I will program a new set of roms. If that doesn't do the trick... well, I'll need to get serious and learn how to use a logic probe and follow traces.
 
Looking your original post again, the jailbars in your graphics reminds me of the jailbars I was seeing on an M72 I repaired a few months ago. The jailbars on the faulty M72 was from two failed KNA6034201 customs - they stream data from the graphics EPROMs and push the data out to the line buffers. We don’t have schematics for M92 unfortunately but I wonder if it’s a similar chip on your board that’s having trouble. It could be the line buffer SRAM as well - the line buffer feeds each horizontal line of graphics to the CRT gun as it draws each line.

Let me do some more research on the M92 hardware tomorrow when I have more time and a board in front of me.

Are the jailbars only on those columns on the right side of the screen? And do they show at all times no matter what’s being displayed?

Also, do you have another M92 board? It would be helpful to swap upper and lower boards with a known good one to isolate whether it’s your top board or bottom board that’s causing the fault. I could possibly loan you an M92 board for comparison testing if need be.
 
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Thanks, I appreciate it. I'll start messing around with the logic probe this week.

The jailbars are consistent/only present where they show in the picture. They are constantly showing - but depending on the graphics layer shown they can be covered up (e.g., the title screen obscures most of them).

Nope, just got the one board. I'm certainly open to swapping boards for comparison.
 
OK, knowing that the title screen covers them up is helpful. I’ll do some research and post back here again in a day or so.
 
Thanks for the video - that’s very helpful.

The M92 supports three tiled background layers and it looks to me like the jailbars are affecting one of them. There’s three large custom chips involved - the OBJ27504A1 custom on the bottom board that streams data out of the graphics ROMs, and the GA21 and GA22 customs in the lower-right corner on the top board that render the graphics data. Physically press down on each chip with your thumb while the game is running and see if the jailbars flicker at all. I suspect that one of the customs has a loose leg or two and needs to have its solder joints reflowed.

If pressing on each custom chip doesn’t make any difference then shoot me a PM and I can loan you a working M92 board set that you can test your board set against so we can narrow the problem down to either your top board or bottom board.
 
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