Backup RAM area

Neo Geo MV1FZS Battery and Backup RAM Error Fix

After having a great time with my MV2FS I was looking for something more compact that I could use in the living room. I came across a pre-consolized MV1FZS and played the entire Neo Geo library with it.

Consolized MV1FZS
Consolized MV1FZS

Then it suddenly stopped working:
BACKUP RAM ERROR
ADDRESS WRITE READ
00D00000 5555 B255

BACKUP RAM ERROR WRITE 5555 READ B255
BACKUP RAM ERROR WRITE 5555 READ B255

Up to that point, I avoided opening it up because it looked too suspicious from the outside. When I finally openend it, the inside turned out to be a mess of dust, wires and hot-glue, just as I as expected.

Consolized MV1FZS - inside
Consolized MV1FZS – inside

This is the BACK UP AREA, which holds the cause of the error most likely. The person who consolized this machine did not remove the coin battery. This is the first thing that must be done when touching a MVS board, otherwise the old battery will leak and eat through the circuit board.

Backup RAM area
Backup RAM area

Battery Fix

The back of the PCB is still protected by a sticker. All the goo needs to be removed before the back up area can be accessed.

MV1FZS PCB
MV1FZS PCB

The battery also has to go, along with some components of the charging circuit. (D1, D2 and R3; see Jamma Nation X and mmmonkey for tutorials)

Battery charging circuit
Battery charging circuit

Now there is much less dust than before, and I also inserted a new coin cell holder for easy battery replacement:

Backup RAM area - battery holder
Backup RAM area – battery holder

At this stage, the error still persists. One way to bypass this error is by using the Universe BIOS to force the Neo Geo into AES (home) mode. While this is sufficient to play the games, you will lose all MVS and backup memory features (e.g. insert coins, book-keeping, save settings and scores).

BACKUP RAM ERROR - UniBIOS bypass
BACKUP RAM ERROR – UniBIOS bypass

Backup RAM Error Fix

I searched the www and found many similar errors (e.g. in this forum). Fixing involved a lot a tracing and even replacing of the memory chips. As all of the traces were fine, I did not want to go so far and replace the memory. Eventually I came across this page which suggested to replace the 74HC32A (quad 2-input OR gate) logic chip U17.

U17 - 74HC32
U17 – 74HC32

The package of the original Toshiba chip is called SOP14 and larger than the more common SOIC-14 replacement chips.

Toshiba SOP14 vs. Motorola SOIC-14:

74HC32 SOP14 vs SOIC-14
74HC32 SOP14 vs SOIC-14

The pins still align, so it is easy to use the smaller package with the help of some solder. Even though it looks ugly, it works.

Backup RAM area - fixed
Backup RAM area – fixed

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