eprom on EWROM board not working EDIT: working now, but why?

I'm trying to socket the prg chip on an EWROM board- HVC-EWROM from a Sangokusi Ii cart to be specific. It does not seem to work. I'm wondering if I am missing something.

1. reasonably sure the board is good- was able to boot the game before removing the stock prg.

2. reasonably sure my eprom is good and appropriate- using 27C020

3. reasonably sure the data is good - dumped the stock prg and compared it with a good rom and bootgod db and wrote the chip and read it back and everything seems right.

4. wiring:

pin 1 up
pin 2 -> hole 24 (a16)
pin 24 -> hole 16 (gnd)
pin 30 -> hole 1 (a17)

just get gray screen at power on. I'm primarily using a famicom to try it out but also tried in a NES with the gyromite adapter.

Any ideas what the issue might be? I'm about at the limit of my diagnostic abilities here.

super frustrated here. i pulled the socket to start over and have been tracing holes to the mmc5 to verify how an eprom needs to be rewired.

I'm using this document for mmc5 pinout:

http://kevtris.org/mappers/mmc5/index.html

based on what i've traced so far, I have this:



16 and 22 are connected via plane, I'm going to assume that's GND and 22 is /OE or /CE
32 is on a different plane, I will take that as 5V for Vcc

A06 seems to be in the right spot on pin 6
I think A07 is on pin 5, and I'm guessing without looking that pins 7-15 are ok

pretty much everything else I've traced here makes no sense.

so, can someone confirm the kevtris page is correct or not? if it's not, is there a correct version? the nesdev wiki seems to be the same.

if it is correct, wtf is going on with my board?

Your pins seem to be almost entirely off by one from the MMC5 mask rom pinout as documented on the wiki.

yeah, it seems like the pins at 58 to 70-something are off by 1.

Here's my tracing work so far:


assuming i'm following the traces on the back to the right remote point, and i'm getting the path right under the resistor, does anything jump out as being wrong with here?

There's a zag you missed in your tracing under the white silkscreening that looks like

dammit I see it now. thanks for pointing that out. i'll start over.

hooray, I got it working. Can someone explain why I had to run pin 24 (/OE) to hole 31, which traces back to the MMC5?

I used this arrangement for 27C020/040:

pin 1 (Vpp) up
pin 2 (A16) -> hole 24
pin 24 (/OE) -> hole 31 /CE from MMC5 ??
pin 30 (A17) -> hole 1
pin 31 (A18) -> hole 2

I only tried it with a 2mbit chip to verify it's working.

I'm using to connecting pin 24 to pin 16 to tie it permanently low. Is that wrong? Why do I have to connect it to the MMC5 in this situation?

fyi I retraced the important parts and this is what I came up with:

Be sure to disable the lockout chip on your NES with this one folks. I being
the silly fella I am totally forgot there wasn't a lockout chip in the fami-adaptor
I was using and it wouldn't boot at all. Soon as I disabled the lockout chip all
was well.

For all the mappers that come to mind tying /OE to gnd is the right thing to do. Obviously from your experiences this isn't the case for MMC5. The mapper is obviously controlling that line which isn't normal for most mappers. They must have had some reason to do this differently for MMC5, although I can't imagine it's of much use...

Maybe something to do with ExRAM or all the PRG-RAM chips it could support? Maybe because of some board configuration they never even used.