Backup RAM errors...

Got three faulty 1-slots (models MV1A and MV1FZ) from an arcade op, all with back up ram errors. When you get a READ 55xx (where x=any number), then the problem is related to the "lower" ram, that is the ram whose data lines (D0-D7) are connected to D0-D7 of the CPU. When you get a READ xx55, the problem is the "higher" ram, with data lines connected to D8-D15 of the CPU. Check Nightmare Tony's many and very useful posts on the subject.

The MV1FZ, which I dealt with for first, gave this error:
http://img.photobucket.com/albums/v65/nassivera/backupramerror1.jpg

At first I thought it was a bad lower ram that needed to be replaced. However after having replaced it I still got the same error which meant the ram wasn't bad at all. A more accurate continuity test revealed that the connection between pin 27 (write enable) of the ram and pin 8 of the 74HC32 (location U17) was broken somewhere (not visible). Connecting these pins with a wire fixed the problem completely:

http://img.photobucket.com/albums/v65/nassivera/neoram8.jpg

So when I set out to fix the other two boards (that were giving similar error messages) the first thing I did was check the same connection and much to my surprise both boards had the same problem:

http://img.photobucket.com/albums/v65/nassivera/backupramerror2.jpg
http://img.photobucket.com/albums/v65/nassivera/backupramfixed2.jpg

MV1A: ADDRESS 00D0000 WRITE 5555 READ 5540
http://img.photobucket.com/albums/v65/nassivera/backupramfixed1.jpg

In these cases too it was practically impossible to see the exact point where the trace was broken, it certainly wasn't due to an accidental scratch either on parts or solder side. I assume it was corrosion in one of the points where the traces change side. It may be noted that the printed circuit on these 1995 boards has the same quality of high serial home systems, a quality definitely inferior in my view to that of the early MVS boards (MV1, 6-slots, older 4-slots) and low serial AES. I think the failures had partly to do with this cheaper PCB quality.

Now this is incredible...

besides the 1-slots I also got a 2-slot from the same arcade op, again with a backup ram error but this time it involved both ram chips:

http://img.photobucket.com/albums/v65/nassivera/backupramerror2-slot2.jpg

And guess what the problem was?

http://img.photobucket.com/albums/v65/nassivera/backupramfixed3.jpg

yup, both rams had the same broken trace from pin 27 to the 74HC32...

Problems were not over though as after repairing the ram traces the board booted with a calendar error:

http://img.photobucket.com/albums/v65/nassivera/calendarerror.jpg

This was due to a certain trace broken in three (!) points. Repairing this trace gave me a fully working 2-slot:

http://img.photobucket.com/albums/v65/nassivera/calendarerror2.jpg
http://img.photobucket.com/albums/v65/nassivera/calendarerror3.jpg

And I have yet another faulty 1-slot from the same op...

Great info you've gathered up -- should help a lot of people...

Jeff

Nice work MKL

Re your sig quote.

"Originally Posted by ttooddddyy
I wish to own a home system. The cabs are sweet but I need AES badly"

Did I really say that ?

lol yes you did, I was searching the archives yesterday and found this:

http://www.neo-geo.com/forums/showthread.php?t=60016

and you really sound serious about it

one too many beer that day or what?

Thanks for the info MKL, I will surely try to get falty MVS boards for real cheap in hopes of getting a hidden gem.

JMKurtz said:

Great info you've gathered up -- should help a lot of people...

Jeff

Click to expand...

Yea,... Ditto..

Man is that interesting..

...................................
This should be stickied or something,so it doesn't get lost ..
Just make it one big Backup RAM error thread..(stickied)

MKL said:

lol yes you did, I was searching the archives yesterday and found this:

http://www.neo-geo.com/forums/showthread.php?t=60016

and you really sound serious about it

one too many beer that day or what?

Click to expand...

Must have been an imposter using my account

I just aquired a 4-slot with a backup ram error:
Address Write Read
00D00000 5555 55FF
From what I understand from the previous posts, this is a lower ram issue, but where is the lower ram located on a 4-slot... connectors on three sides

edit- I just swapped the upper board with a 4-slot with a test hatch screen issue that battery fixing didn't fix (:[), and got a different read number for it... I got B240... what would this mean (if anything)?

Well, this is the pinout for the CPU and backup RAM so you can figure out which is which:

http://img394.imageshack.us/img394/2429/68000ram7rv.png

Do you always get that error (55FF) without swapping the top board?

As for the B240 error, there are a couple of old posts by Nightmare Tony where he says it's quite a nasty problem.

Thanks for teh pinouts. WHere on the mobo are these chips? If they're on the upper board, then it's alright, because I already know that mobo set has issues, and can just let it be, but if it's on the lower, I may have a bit more trouble... I can fix broken traces, but desoldering a whole IC is a pain in the ass, and I would rather not have to do it. I did a search, and came up with two other threads about the B240 issue... they don't really say what exactly to do in that situation, other than don't buy...

All the ram is on the bottom board:

http://img208.imageshack.us/img208/6746/4slotram4ux.jpg

If you have this 4-slot (older model) the Toshiba flatpack chips (marked 43256 on the PCB) are from the top:

video ram
video ram
work ram
work ram
backup ram (lower)
backup ram (higher)

If you have a different 4-slot look for the same chips (they could also be Sony) and those that don't have pin 28 connected to the main 5v rail are the backup ram.

ok... wtf? I get way different than I think I should be getting... If I'm reading right, I should get (on the left) and what I read (on the right)

pin on backup ram to pin on cpu to actual pin on cpu
1-42-26
2-40-23
3-35-36
4-34-35
5-33-34
6-32-33
7-31-32
8-30-31
9-29-30
10-N/C-29
11-N/C-61
12-N/C-60
13-N/C-59
14-N/C-16/53

28-14/49-n/c
27-N/C-n/c
26-41-42
25-36-37
24-37-38
23-39-40
22-N/C-n/c
21-38-39
20-N/C-n/c
19-N/C-54
18-N/C-55
17-N/C-56
16-N/C-57
15-N/C-58

these are my readings from the chip located at h7 and 8, labelled 68000-12.
This seems a bit TOO far off from what it should be... only three pins are reading what I think they should be... and they're all reading nothing... so, what's the deal?

Note that the address lines on the CPU start with A1 while on the RAM they start with A0. Sorry for the discrepancy but that's the only picture I could find...
So the connections should be like:

RAM___CPU

1______43
2______41
3______36
4______35
5______34
6______33
7______32
8______31
9______30
10_____29
21_____39
23_____40
24_____38
25_____37
26_____42

etc.

There are 3 pins for each backup ram chip that are not connected to the CPU:

lower ram:

20_____74HC32 (13) located at D10
22_____PRO-C0 (16)
27_____74HC32 (8) located at D10

higher ram:

20_____74HC32 (13) located at D10
22_____PRO-C0 (8)
27_____74HC32 (6) located at D10

I really need to dig up my one slot with the dead backup ram and see if this can help

great info, thanks

double post of the post below so i have removed it!

(cant have 2 pictures on that large side!)

I know this thread is 6 years old! but it today helped me fix a MV-1AX board with the backup ram ADDRESS 00D00000 WRITE 5555 READ B255

It was indeed RAM4 pin 27 not making continuity with pin 3 of the 74HC32, but insted of running a wire back to the 74HC32 i decided to trace where the open circuit was. I discovered it was ok untill just before the track ran under the RAM3 chip, so did a wire jumper from the through hole to the RAM4 pin. Have put a pic below as looking carefully you can just see where the green lacquer changes colour! this i suspect is where the open circuit occured!




Cheers
Andrew

Sure you zoomed in on that close enough?

yes i think thats just about close enough!
quite suprised it came out as well as it did!

Hi, this is my first post here. I recently got a beatup MV2 with backup ram ADDRESS 00D00010 WRITE 5555 READ 5540. Any 100% tips what to do other than probing the shit out of the board? Greets and thanks

Check the lower backup RAM, could be corrosion.

Yeah, thanks for your kind answer, will report back If we get it fixed!

Any news about this? I have this problem:

00D00000 5555 5540

On a Neo-MVH MV2-01

Will post pics soon.

I cleaned it thoroughly with an old toothbrush and cleaning alcohol. Now it is getting some sort of artifacted green screen (will make a video). Is this a sign that I just worsened the problem or may this be some sign of getting better?

Good sign I guess. That's the (stuck on green) calendar error screen. Check the battery and RTC area for corrosion and bad traces. Also check the crystal, those will often fail from corrosion as well.