mv1a not saving

littlecharlie

Neo Bubble Buster
Joined
Jan 10, 2018
Posts
52
Hi, my mv1a is not saving hiscores or unibios options.

I have encountered this problem before in other boards and was able to solve it either fixing a broken trace or replacing a component.
But this time I think I have covered everything and still not working.

I've done the basics, like erasing the backup ram in the bios, and checking that the BRAMs get above 3V all the time.

I've replaced both upper and lower BRAMs with new RAMs chips, and the 74HC32 beside them as well, which sometimes is the culprit.

I've checked all traces and they all seem good. I've checked the connections between both BRAMs and the BIOS(SP1) and the 68k. All fine.

Any ideas?
 

Neo Alec

King of Spammers
20 Year Member
Joined
Dec 7, 2000
Posts
10,277
I just removed the stock battery and replaced it with a socket and a LIR2430, so the charging circuit remains untouched.
The replacement battery used to work? That's the part that was worked on, so it seems like the most obvious thing to double check.
 

littlecharlie

Neo Bubble Buster
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Jan 10, 2018
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I didn't check when I got the board. I directly replace the old battery with a socket. The work was minimal.

I have done more checks: I've monitorized the pin Vcc of the RAMs in the Oscilloscope, and it goes from 4.8 v when on (5v power source) to 3.2 v when off (from the battery). No drop to zero in between. So the RAMs are getting enough voltage at all times.

I'm really missing what is going wrong.
 

maki

Krauser's Shoe Shiner
Joined
Jan 1, 2022
Posts
231
did you use a 161-in-1 cart?
IIRC those reset the settings/hiscores
 

littlecharlie

Neo Bubble Buster
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Jan 10, 2018
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That's true, those carts erase hiscores but normally they don't reset the Unibios settings (if you set for example your board to "Console", it remains that way).
But in any case, for all the tests that I'm doing I only use original carts (just to avoid any malfunction due to the 161 cart).

The 3 saving features that are erased every time i turn off/on the board are:
1- Hiscores
2- Soft dipswitches (like blood on MS) settings
3- Unibios seetings (Console/Arcade and Region)

BTW, apart from that, the board works great (audio and video).
 

ack

Fio's Quartermaster
10 Year Member
Joined
Apr 9, 2009
Posts
481
I would try the diag bios and see if it finds anything. Backup ram is read-only by default and requires some logic for it to become writable. Perhaps there is something broken with that.

other random things

- make sure you aren't picking console mode in unibios. neo geo consoles don't have backup ram so the game wouldn't even try to save hi scores.
- any chance the backup ram is not original chips? its possible replacement chips don't support keeping their contents with only ~3V from a battery
 

littlecharlie

Neo Bubble Buster
Joined
Jan 10, 2018
Posts
52
Thanks for the tips ack

The diag bios says all tests pass, and if a go to the specific BRAM test, it starts counting (not sure exactly what or up to how long), so I guess the BRAM is OK.
The second part you mention, you mean to check the signals WE/, OE/ and CS/?

Reagarding the new BRAM chips, there are not original (meaning they were not taken from another MVS), I bought them online . So it could be what you are suggesting (although I'm pretty certain I used the same brand/characteristics in another board repair).

Edit:
I added another 5v DC power supply directly to the battery circuit, so the RAMs get 5v at all times (when the board is on and also off).
Again, after an off and on, no settings are saved. So I'm ruling out that possibility.
 
Last edited:

ack

Fio's Quartermaster
10 Year Member
Joined
Apr 9, 2009
Posts
481
whats the model number on the chips?
 

littlecharlie

Neo Bubble Buster
Joined
Jan 10, 2018
Posts
52
I've tried 2 brands, ISSI 62c256AL-45ULI and SEC KM62256CLG-7L
the orginals were UM62256DM-70LL
 

littlecharlie

Neo Bubble Buster
Joined
Jan 10, 2018
Posts
52
I'm stuck with this.
The RAM chips are not the problem, I have replaced them with RAM chips working from another board, and still the same problem.

So far:
- checked both RAMs chips
- checked the 74HC32
- no errors with the diagnostic bios
- checked traces (they all seem OK)
- cleared backup RAM
- checked the battery circuit
- I have added (just to make another check) a continuous 5v independent power supply directly to the battery circuit, so the chips get 5v at all times. Still no saves after power off and on.

Any new ideas?
 
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