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There's no way that's right: that has to have been shorted together when it shouldn't,

You were right. I checked against one of the other boards I have and it looks like I shorted a trace under the socket (the solder wandered).

After fixing that, I'm still seeing the following from the CHR rom using Megaman 3 (the EPROMs work right on a 51555-2 board):

http://imgur.com/a/ULfdN

Are MC-ACC pin-compatible with EPROMs?

I have a few of these carts and there's no way to really tell the difference from the label - they all look the same. Some are 51555-2 (MMC3B) and others are MC-ACC boards.

Thanks again for your help.

I am reasonably confident that all the resist-lacking Acclaim PCBs just used standard JEDEC pinouts, and that that is the same as UVEPROM pinout for 1 and 2 Mibit ROMs...

But then I don't know what GameMachineJames's comment was about. Where in which Mega Man is that? It shouldn't be too hard to figure out what bank is being displayed vs which one was requested, and after we have that information it'll hopefully shed light on what's wrong.

On some level, given the picture, it has to be "the upper address lines are wrong" but that's so vague as to be useless.

This is Mega Man 3 (NA) using the Akklaim (Acclaim) MC-ACC MMC3 clone [53361-2 board] from a Roger Clemens MVP donor. The two other screen shots are from Shadow Man's intro and from the first part of the level.

The EPROMs are 27c020 UV EPROMs. The CHR ROM is doubled up to fit onto the EPROM (Mega Man 3's CHR is 128Kb). PRG is 256Kb. They work perfectly fine on another Roger Clemens board with a proper MMC3B on it.

http://imgur.com/a/trzm6 (works properly, I have this board with sockets installed for testing)

http://imgur.com/a/4bs9h (errors in CHR) <-- this is the board I'm working with. Same donor (in name only), same EPROMs.

Video of the CHR errors: http://sendvid.com/r67me113 - as you can see, it seems like it can read the first portion of the ROMs (notice how everything in the level select looks right), but maybe it can't switch banks properly? I'm not sure. There's not a lot of info on how to rewire MC-ACC boards.

Thanks for your help.

edit: Just a thought.. perhaps CHR only needs to fill half of the EPROM, and the other half needs to be zero-filled? (Something about it being pulled "high" or "low"?)

So somehow it's selecting the wrong bank.
On the first screen:
* The boss selector is tiles in banks $7C-$7F, all tiles. Additionally sprites from bank $34 are used to fill in white-person-skin-tone bits. All display correctly.
* When Shadow Man is supposed to be striking a pose, his sprite tiles are supposed to be bank $2F, and the sprites are tile indices $F8 through $FB. Instead we see the smirk portion of a face, which comes from bank ... $3F.

On the next screen:
* All the background tiles are supposed to be from banks $5C-$5E, indices $0C-$0F at the top line; $1C-$1F and $2C-$2F in the middle; $3C-$3F above the platform, and instead we see the letters that are in bank ... $7C-$7E.
* Mega Man's sprites are in bank $00, and they display correctly.

In the first case, the A14 line is high when it shouldn't be; in the second case, the A15 line is high when it shouldn't be. And ... that's all I can tell. I don't know whether it's a wiring problem (although GameMachineJames implied it is) or a logic problem or whether the wiring problem is between the ROM and PPU, PPU and mapper, or CPU and mapper. But if I had to take a guess, I'd look closely for a short between CHR A14 and A15.

I'm confident it's not that...

Wow. I'm blown away. Good call.

There was a tiny solder blob under A15 that was shorting to A14.

THANK YOU! It works perfectly now.

By the way, we have an old kinda-dubious pinout of the MC-ACC here ... but
There is the possibility, if the pinout is correct, that pin #39 on the MC-ACC might be PRG A18. At least, in terms of spacing it's right.

No idea what the disconnected pins 6-8 are. They might be an enable for RAM, though.

If you feel up to it, you could consider this a request for verifying the pinout that old post...

I have one more MC-ACC board left, I'll give it a shot.

I was able to get Mega Man 3 running on my dev/test (socketed) board, I'll run the MMC test suite on it this weekend.

Thanks again for your help!

Question for genepensive

So, in the end, what wiring did you have success with for each type of acclaim board (51555-2 and 53361-2)? Is it just standard TLROM wiring or did you have to make additional changes?

I had success with both. There was no re-wiring required, just drop the EPROMs in, IIRC. I'll verify for you this weekend.

The biggest issue was that the pins are so easily shorted..

Yeah that actually worked! I got a TLROM running on a 53361-2 (w/40 pin mmc3 clone). No bending pins, no wires. Just dropped in two 4mbit chips.

The PRG socket wiring didn't quite match a normal TLROM board PRG socket. I started to go through tracing every wire, but then I figured why waste the time I could always take the chip out if that didn't work.

Thanks for the help!