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MV-1A Issues – Salvageable?

CMYKhazi-Dan

CMYKhazi-Dan

Student
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Nov 11, 2021
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Near Bournemouth, UK
I have acquired a couple of MVS boards and some carts but the MV-1A gives me a Backup RAM Error.
The board is quite clean and nice, I assume got it's original battery, the JAMMA connector looks a bit worn.

This is what it does...

After leaving it a while before powering on I get greeted with this screen...

1-slot-error-01.jpg
If I press A, B or D I get a black screen with some buzzing. I power it off and on again and this screen appears...

1-slot-error-02.jpg
and also this one amongst others with one line of text like FFAFF

1-slot-error-03.jpg
Power off then back on again, black screen and some buzzing.
I am using it with a UniBIOS 4.0 as the original BIOS just gives me these crazy flashing alternating images!

1-slot-error-04.jpg

1-slot-error-05.jpg

Expert advice on whether this is fixable would be most welcome and appreciated – thanks in advance ^^
 
This appears to be a common issue. Check for continuity of the traces around the battery. And also remove the original battery.
 
Its' a bad 256 near the backup ram. Write and Adress should match, looks like the upper data is corrupted. If i remember right the upper ram is the closest to the jamma edge
 
Neo-Alec said:
And also remove the original battery.
Click to expand...
I was waiting for this advice – what does this actually do? I have a third board that has the battery removed but it only works with the UniBIOS not the original BIOS
 
your removing it:
1 - to stop it leaking
2 - to inspect under it incase it has leaked or a previous one leaked
3 - because you want to do a coincell mod when it's fixed anyway

btw, if your board wont run with stock bios then you may have a clock-chip issue.
no real surprise as it's battery related.
 
stj said:
btw, if your board wont run with stock bios then you may have a clock-chip issue.
no real surprise as it's battery related.
Click to expand...
The other board I referenced – my main one, an MV-1 – looks like the battery leaked at one point and corroded the crystal that was next to it. I was going to sort it out but never got around to it, was also a bit reluctant as I'm quite good at destroying PCBs :D
 
stj said:
your removing it:
1 - to stop it leaking
2 - to inspect under it incase it has leaked or a previous one leaked
3 - because you want to do a coincell mod when it's fixed anyway
Click to expand...
and
CMYKhazi-Dan said:
The other board I referenced – my main one, an MV-1 – looks like the battery leaked at one point and corroded the crystal that was next to it. I was going to sort it out but never got around to it, was also a bit reluctant as I'm quite good at destroying PCBs :D
Click to expand...
if it hit the crystal then you should probably replace the 2 related ceramic capacitors too.
 
IIRC, the MV1A has the lithium battery so you should be fine there as they don't normally leak. On the ones with NiCd they leak and eat traces causing hell with that backup RAM section.

You have a problem with the Backup RAM on the upper data lines. It's an 8 bit RAM chip tied to a 16 bit data bus so there are 2 of those RAM chips to meet the 16 bit data path of the CPU.

I don't have a 1A in front of me so the only advice I can give is to get the pinout of the 68000 CPU and check continuity of its data pins to pins 11 to 13 and 15 through 19 of the Backup RAMs. One will be tied to D0-D7 and isn't showing the error while the other is tied to D8-D15 and will be the one you need to replace.

The Backup RAM and the Work RAM are both tied to the CPU's data bus. You can tell them apart by checking pin 28. While out of the cabinet the Backup RAM will have battery voltage on pin 28 (If the battery has voltage) where the work RAM will not. If the battery is flat check contiunity of pin 28 to the +5v pins on the JAMMA edge connector. The work RAM will have contiuity to it while the Backup RAM will not.
 
Pictures 2 and 3 give the impression you have trace corrosion (trace is dark/black under solder mask) all over the place.
 
Check the continuity, but with the error you're getting, it looks like a bad chip to me.
 
Cheers guys, so is this thing worth bothering with? I bought it along with a working MV1B board, genuine Metal Slug cart, genuine Puzzle De Pon cart and what appears to be a bootleg Puzzle Bobble cart for £130. Guy said he would give me a refund for non-genuine or non-working items.
 
so what i start with,
scrape the green laquer off with the BACK of a knife and give it a couple of strokes with a fiberglass brush,
then tin it with solder to add a protective layer.
then check it with a meter - if it really has a break then solder a strand of copper wire along the track over the break.
 
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