Making a cart from scratch...

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Joe
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Re: Making a cart from scratch...

Post by Joe » Wed Mar 24, 2021 8:27 pm

It sounds like you have a counterfeit EPROM. Set your programmer to Fairchild/National Semiconductor NMC27C64Q and see if that helps.

But that assumes there are no other problems with them. (250ns is fast enough, right?)

the_wizard_666
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Re: Making a cart from scratch...

Post by the_wizard_666 » Wed Mar 24, 2021 8:41 pm

Well, I may have found another possible issue. The output on Famirom for the CHR chip is 2764, but my chips are 27C64. Gonna try my 128s and output for those instead, see if perhaps that changes things before I go too crazy on it. Switching the chip type worked, it detects it just fine now.

lidnariq
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Re: Making a cart from scratch...

Post by lidnariq » Wed Mar 24, 2021 8:44 pm

The "C" in the middle almost certainly doesn't matter, in this case. But as long as you have an erase you may as well see if using a 27'128 helps any.

the_wizard_666
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Re: Making a cart from scratch...

Post by the_wizard_666 » Wed Mar 24, 2021 9:00 pm

Well, I don't have an eraser, nor do I have the copper braid I need to desolder, but a friend of mine has both so I'll do the work at his place on the weekend. What I do have is 20 of each EPROM chip, and a couple extra boards to play with. So while removing chips will wait until the weekend, I have some room to test things out.

So, I tried a different ROM. This one had a smaller PRG but the same size CHR, so I used the 64K chip to test it out. Long story short, game boots with the same sort of graphic issues. So the way I see it, there could be a couple possibilities, both of which I'll check for. First, I'm going to do a third NROM game (might as well mix it up if there's no issues) and use a 128K chip. If that works fine, odds are it's just a matter of using a larger CHR chip. If it doesn't, I'll await the arrival of my capacitors and put those on the boards. Not sure what else could be the problem - it's clearly loading the PRG because the audio plays. Even though the visuals are garbled, at least I know something is loading.

lidnariq
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Re: Making a cart from scratch...

Post by lidnariq » Wed Mar 24, 2021 9:14 pm

It might help if you shared a picture of one of the garbled screens ... and told us what game was supposed to be onscreen too.

the_wizard_666
Posts: 37
Joined: Thu Feb 25, 2021 2:46 pm

Re: Making a cart from scratch...

Post by the_wizard_666 » Wed Mar 24, 2021 9:25 pm

lidnariq wrote:
Wed Mar 24, 2021 9:14 pm
It might help if you shared a picture of one of the garbled screens ... and told us what game was supposed to be onscreen too.
Cart 1: The Mad Wizard
IMG_20210324_221901346.jpg
Cart 2: Mahjong
IMG_20210324_221829019.jpg
Additionally, I played a few screens of Mad Wizard, and other than the visuals there are no issues...game plays fine, and the audio is perfect.

the_wizard_666
Posts: 37
Joined: Thu Feb 25, 2021 2:46 pm

Re: Making a cart from scratch...

Post by the_wizard_666 » Wed Mar 24, 2021 11:03 pm

Tested it out with a 128 CHR and it works fine. Guess it was chip compatibility after all. Thanks for the help guys :)

Oh, and another stupid ass noob question before it becomes an issue - if the CHR portion is nonexistent, do I still need to put a chip in? I'm assuming it wouldn't require data or anything, but I'm unclear whether it physically needs to be there. Thanks again!

lidnariq
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Re: Making a cart from scratch...

Post by lidnariq » Thu Mar 25, 2021 12:42 am

the_wizard_666 wrote:
Wed Mar 24, 2021 11:03 pm
Tested it out with a 128 CHR and it works fine. Guess it was chip compatibility after all. Thanks for the help guys :)
There's got to be something weird going on with those 8KB 'PROMs that causes that nonsense to show up ... but I have to admit I have no idea what it could be.
if the CHR portion is nonexistent, do I still need to put a chip in?
You'll need a SRAM. Almost always 8KB, but there are a very short list of original contemporary games that used more, and a longer list of modern homebrew (you can't actually buy new RAMs smaller than 32KB anymore)

Joe
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Re: Making a cart from scratch...

Post by Joe » Thu Mar 25, 2021 11:25 am

the_wizard_666 wrote:
Wed Mar 24, 2021 9:25 pm
Cart 1: The Mad Wizard
Are you sure this game uses CHR ROM? The copy I found uses CHR RAM...

lidnariq
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Location: Seattle

Re: Making a cart from scratch...

Post by lidnariq » Thu Mar 25, 2021 11:32 am

The demo is NROM; the later full release is UNROM

the_wizard_666
Posts: 37
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Re: Making a cart from scratch...

Post by the_wizard_666 » Thu Mar 25, 2021 12:01 pm

Yeah, found out after it was a demo version. D'OH! At least I figured out the issue though. Was mostly just trying to test some games to get the process down before doing the bigger, good stuff :P

the_wizard_666
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Re: Making a cart from scratch...

Post by the_wizard_666 » Fri Mar 26, 2021 3:56 pm

Joe wrote:
Wed Mar 24, 2021 8:27 pm
It sounds like you have a counterfeit EPROM. Set your programmer to Fairchild/National Semiconductor NMC27C64Q and see if that helps.

But that assumes there are no other problems with them. (250ns is fast enough, right?)
It appears I just found another counterfeit - this time it's an AM27C040 -120DC ...is there a list of counterfeits that I can check against, because I feel like this kind of issue is gonna keep coming up if I keep buying chips from China. Device ID comes up as 20 41 if that helps. I tried unchecking the check ID box on the burner software and ended up with a programming error, and as I only bought 5 of these chips, I'd like to get it figured out without having to blow through them all.

And thanks again for all the help. I know I keep popping total noob questions, and I know from my own experience on other forums how tedious these kind of threads can get. I tried searching, but it's a needle in a haystack. I'm just thankful that you are such a great bunch of people here, cuz I already feel like an idiot as it is :P So yeah, thanks for being so chill :)

lidnariq
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Re: Making a cart from scratch...

Post by lidnariq » Fri Mar 26, 2021 4:15 pm

is there a list of counterfeits that I can check against, because I feel like this kind of issue is gonna keep coming up if I keep buying chips from China.
Probably not. Even if the markings aren't counterfeit, you still don't know that it was working.
the_wizard_666 wrote:
Fri Mar 26, 2021 3:56 pm
Device ID comes up as 20 41 if that helps.
M27C4001, M27V401, or M27W401.

When I was looking around for a "eprom manufacturer code lookup", I found someone mention a specific piece of software ... which I've downloaded ... and discovered embedded into it is a verbatim C header file that contains this information. (Wacky)

I've heavily massaged that, trimmed it, and attached it so that you can do your own lookups. Maybe Joe knows of another database too.
Attachments
prom-manf-and-dev-ids.zip
(18.15 KiB) Downloaded 19 times

Joe
Posts: 460
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Re: Making a cart from scratch...

Post by Joe » Fri Mar 26, 2021 4:55 pm

lidnariq wrote:
Fri Mar 26, 2021 4:15 pm
the_wizard_666 wrote:
Fri Mar 26, 2021 3:56 pm
Device ID comes up as 20 41 if that helps.
M27C4001, M27V401, or M27W401.
Careful: M27V401 and M27W401 are 3.3V and require level shifters. You probably shouldn't use these chips.
lidnariq wrote:
Fri Mar 26, 2021 4:15 pm
Maybe Joe knows of another database too.
I'm pretty sure we're using the same database, except yours is newer (I found an old copy of the C header posted on a forum somewhere).

lidnariq
Posts: 10456
Joined: Sun Apr 13, 2008 11:12 am
Location: Seattle

Re: Making a cart from scratch...

Post by lidnariq » Fri Mar 26, 2021 5:05 pm

Joe wrote:
Fri Mar 26, 2021 4:55 pm
Careful: M27V401 and M27W401 are 3.3V and require level shifters. You probably shouldn't use these chips.
Both, despite being rated at 3.3V, have Absolute Maximum Rating of up to 7V on Vcc, so ... it might actually be ok. I don't know. The official programming process involves supplying Vcc=6.25V, so they have to work enough for verification at that voltage... wish I knew what it meant when one read this high of a rating relative to the intended operating conditions.

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