MVS 2 Slot Repair Help
- Thread starter r67055
- Start date
what should I watch? to fix the graphics bug?
I would look around the NEO-ZMC2 ic which is next to the hard dips. It common for battery leakage to cause damage which leads to sprite issues on 2 slot boards.
https://wiki.neogeodev.org/index.php?title=NEO-ZMC2
The path of sprite data goes SLOTS -> NEO-257s (picks the active slot) -> NEO-ZMC2 -> NEO-B1
https://wiki.neogeodev.org/index.php?title=NEO-ZMC2
The path of sprite data goes SLOTS -> NEO-257s (picks the active slot) -> NEO-ZMC2 -> NEO-B1
the battery did not leak. unfortunately, the zmc2 has such a tight leg distribution that I don't dare to start replacing it. it needs good quality flux, which I don't have at the moment. I'll look it over. I don't suspect the NEO-257 because the same error is visible in both slots.. I was very happy that I made it this far. in the morning I also loaded the 4slot mvs. produces the same error as this pcb.
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can you watch the bits?
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This is a different board? it says you are on slot 4. That one looks like the upper byte is stuck with value 0x61
I forget the button, but there should be a way to switch between slots when in the memory viewer. I would try putting games in all slots then switch between to see if they all have that stuck 0x61 for upper byte.
First thing I would do is look for damage around the battery, the program rom address/data lines run right under/next to it.
To the left of each slot are 2x 74LS245s, these are what the program data lines pass through. The left most one should be the upper byte, and the right one the lower byte. For whatever slot you have up in the memory viewer I would use a logic probe and verify that slot's 245s are getting enabled and passing data.
All of the output pins on those 74LS245's for each slot are tied together and go to CN10 in the lower left, which takes them to the lower board. On the lower board they should land on the 74AS245s @ B7 and B8, then onto the CPU when enabled. Perhaps ones of these is not getting enabled or is broken.
As you trace stuff out this can be useful to know which pins are which on the slots.
https://github.com/jwestfall69/neogeo-diag-bios/blob/master/docs/slot_pins_inserts.md
To the left of each slot are 2x 74LS245s, these are what the program data lines pass through. The left most one should be the upper byte, and the right one the lower byte. For whatever slot you have up in the memory viewer I would use a logic probe and verify that slot's 245s are getting enabled and passing data.
All of the output pins on those 74LS245's for each slot are tied together and go to CN10 in the lower left, which takes them to the lower board. On the lower board they should land on the 74AS245s @ B7 and B8, then onto the CPU when enabled. Perhaps ones of these is not getting enabled or is broken.
As you trace stuff out this can be useful to know which pins are which on the slots.
https://github.com/jwestfall69/neogeo-diag-bios/blob/master/docs/slot_pins_inserts.md
The pins of the two 74AS245 B7 and B8 are connected to the CPU. the Inputs of the 74AS245 are connected to the CN10 pins.
I saw signal levels on the three 74245 outputs and inputs on the upper board.
Unfortunately, I'm not very good at measurements, so I don't know what to look for.
I saw that
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I have a hard time believing that. That first trace looks like its almost completely gone.
Any traces where it goes dark is an indication of corrosion and could be resulting in a break. That picture has them all over.
Any traces where it goes dark is an indication of corrosion and could be resulting in a break. That picture has them all over.
It looks like that one is ok, but you need to check them all. There are darkened traces all round the battery area need to be checked. I would advise cleaning them up, which involves removing the solder mask, tinning them, then covering them back up with enamel or epoxy.