NES - problems converting battery backed SNROM to no battery

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asdfqwer426
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Joined: Sat Nov 23, 2013 7:57 pm

NES - problems converting battery backed SNROM to no battery

Post by asdfqwer426 » Sat Feb 20, 2016 10:44 pm

I've made many NES repros for myself and most have gone fantastically. even ones where i slipped with the dremel and cut traces, i've managed to repair and get working. But I'm having a hard time with one game and i think i'm just missing something.

I'm trying to make a 128kb SNROM game cart for myself, but it just won't work. I've actually made 2 attempts now.

the game is mmc1 and requires both 8kb CHR-RAM and W-RAM, with no battery backup.

I used ultima exodus as my donor (sorry ultima), which has all the right hardware but has battery backed SRAM.

I wired up the eprom as usual and when it got to the battery part, as per the [NESDEV SxROM page](http://wiki.nesdev.com/w/index.php/SxROM), in the "battery data retention" section, i removed the battery, D1, D2, R1, R2, R3, and i connected the SL solder pad. I also removed the extra cap, but tried it both with and without it as the page doesn't mention it.

regretfully i still get a black screen with this game. before i desolder the eproms and start over again, I was curious if theres something simple i'm missing, possibly in the battery conversion process?

thanks!

lidnariq
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Location: Seattle

Re: NES - problems converting battery backed SNROM to no bat

Post by lidnariq » Sat Feb 20, 2016 11:09 pm

Almost always, battery-backed PRG RAM is a subset of not battery-backed. Have you seen if it works without removing the battery?

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tokumaru
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Re: NES - problems converting battery backed SNROM to no bat

Post by tokumaru » Sat Feb 20, 2016 11:20 pm

There shouldn't be any need to remove the battery in the first place...

FrankWDoom
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Joined: Mon Jan 23, 2012 11:27 pm

Re: NES - problems converting battery backed SNROM to no bat

Post by FrankWDoom » Sat Feb 20, 2016 11:46 pm

and if you insist on removing the battery, that's literally the only step. everything else can stay exactly the same.

asdfqwer426
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Joined: Sat Nov 23, 2013 7:57 pm

Re: NES - problems converting battery backed SNROM to no bat

Post by asdfqwer426 » Sun Feb 21, 2016 8:35 am

I'll try adding the parts back into the second one and see what happens i guess.

i followed the traces on them out of curiosity and it seems like all the parts i removed are just power circuit parts. it seems like the point of the SL pad is to reroute power between battery traces or system 5v. Anyone know what effect the SL solder pad has if theres no need to do anything with it?

I suppose it could be my rom file, but i was hoping i'd missed something simple in the wiring.

thanks all.

lidnariq
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Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: NES - problems converting battery backed SNROM to no bat

Post by lidnariq » Sun Feb 21, 2016 1:07 pm

The SL pad shorts out the diode D2, connecting Cart +5V to PRG RAM Vcc always, whereas if the diode is there it makes a simple backed-up power supply that can draw power from +5V when it's higher than the battery voltage.

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HVC-Man
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Re: NES - problems converting battery backed SNROM to no bat

Post by HVC-Man » Mon Aug 01, 2016 6:53 pm

If the game isn't booting, you should look at the PRG ROM and make sure it's wired correctly. A common problem is not lifting EPROM pin 1 and at least leaving it floating. Sometimes you have to tie it to VCC, depends on the model. You can also try setting pin 31 to VCC.

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