nesdev.org

I've been trying for like 2 days to get this right, and I'm at my wit's end.

I have an original Just Breed famicom cart, and it tested working just fine with the original mask roms.

I thought I'd pop the Stealth translation into it via EPROMs, but all I have are MC27C801s (I got a box of like 40 of them from a friend who went to china).

I figured if I wired them up like I've seen on the net for MMC5 reproductions, and tied A19 and (and A18 on the CHR) to GND, the larger EPROMs would be limited to 512KB and 256KB, respectively, and run just fine.

Now, from what I've seen, the MMC5 eprom wiring is as follows:

Bend up pins 1, 2, 24, 30 & 31
pin 1 to hole 30 (grounded on PRG and CHR limit EPROM to 512KB)
pin 2 to hole 24
pin 24 to hole 31
pin 30 to hole 1
pin 31 to hole 2 (grounded on CHR with Pin 1 to limit to 256KB)

However, whenever I to run it on my NES, all I get is a solid color screen.
I can't get any sound, so it's obviously a PRG issue, but I've de-soldered the EPROM TWICE now, re-verified the content, erased and re-burned, then used ENTIRELY NEW CHIPS just to rule that out.

Please help!

Ok, update.

I managed to fix the rom, so it boots.

The problem was the Famicom to NES converter had expansion audio routed from pin 46 to 54 (I have a top loader).

With the pin cut, it runs just fine, but I have, obviously, no expansion audio.

I've seen some guides saying to put 2 10kohm resistors in series on pins 45 and 46.

This seems to make the cart work, but I get NO audio.

Anyone know what is going on?

The FC MMC5 carts explicitly route and amplify audio from the FC. (q.v. http://wiki.nesdev.com/w/index.php/File:MMC5_audio.png )

The NES-ExROM carts, on the other hand, completely omitted R3 and C4, and added R9 in series with the output...presumably to avoid over-loading the output of the MMC5's amplifier.

I'm not certain what I'd do to modify the adapter that wouldn't also pose a problem for other FC carts with audio...

Presumable, then, I could modify the cart itself to remove the audio circuitry, or modify my NES to allow 2A03 audio into the cart?

Yeah. I don't know, though; I'd have thought the 47kΩ mixing resistor as normally prescribed for mixing in audio on the front-loader would have been good enough.

What are you doing to mix audio on the top-loader? It sounds like it's shorting something out, causing the cart to not work. Or maybe you're doing something to the EXP5 pin?

per the powerpak mod, I'd modded my top loader to get audio from Everdrive (viewtopic.php?t=7880)

I have it wired to give output on an eternal phono jack through a 1Kohm trim pot.

So the audio from the cartridge isn't getting mixed in with the system audio at all?

It looks like it was being shorted by something.
I've fixed it, but now the audio is SUPER low on the expansion audio.

I'm looking at the cart for a resistor I can remove, since my 1K pot will only allow a very small level of audio out, so I figure if I lower the resistance of the audio out pin, it will be louder.

Edit-
SOLVED IT!

On the cart, I removed R2, R1, and R4 (6.8Kohm, 15k, 10K, respectively)

I replaced R2 with a 1Kohm resistor, bridged R1 with the the clipped leg of the resistor, and moved the 6.8Kohm resistor into R4.

The volume level with the trim pot for my Expansion Audio at near its a very setting (like 100-300 ohms) gives nearly PERFECT audio levels, and no clipping or pops.
The resistors in question are beneath the battery here:
http://bootgod.dyndns.org:7777/image.php?ImageID=10548

My electrical theory is a little rusty, and I don't perfectly get the layout of the board, but I seem to have stumbled on a nice solution.

On the MMC5 cart, you could try increasing the value of R4 ... that should make it louder, at the risk of potentially clipping.
Reducing R1 should also make it louder, and it's possible that removing R2 or C3 might also.

lidnariq wrote:On the MMC5 cart, you could try increasing the value of R4 ... that should make it louder, at the risk of potentially clipping.
Reducing R1 should also make it louder, and it's possible that removing R2 or C3 might also.

See the above post, I found a nice solution.

there's a little bit of a hiss in the audio, but it's negligible.

I could probably increase R2 to like 2.5-3Kohms to massage that out, but I've spent all damn day on this cart and I just wanna relax now.

R2/C3 should be the MMC5 DAC, which shouldn't be used by Just Breed ... so theoretically you could just remove it.

They seem to do SOMETHING, because when I removed them, the pitch of the expansion audio increased.

It was rather squeaky.

Oh dear. That's ... intensely weird.