I had been interested in picking up Blue’s Journey for my Neo-Geo MVS, however the going price online was a bit too high for my liking. So when I saw a cartridge listed as non-functioning for spares and repairs, I sent over an offer I was happy to risk the chance of not being able to repair it and purchased it as a project.
When the cart arrived I tested it in both my MVS and it would not boot at all.
So I opened up the cartridge to take a look at both the PCB inside:
Nothing looked out of the ordinary apart from the cartridge connector pins being very dirty, so I cleaned them and had to resort to using a Fibreglass Abrasive Cleaning Pencil to remove some corrosion that had started to appear on a few pins.
The MVS cartridge however would still not boot so a closer inspection was required and I found a broken burnt out trace on the rear side of the PROG8M42 (Program) Board:
This was easily repaired by soldering a jumper wire from the cartridge pin to the via:
Unfortunately the Blue’s Journey MVS cartridge would still not boot.
From researching online it became apparent that the reason a lot of MVS carts would not boot was because of a bad program Mask ROM and the only way for me to really test it was to remove it:
Now I needed to figure out a way to read the Mask Rom and for this I needed to find the Eprom equivalent which had the exact same pin out.
The program was situated at the P1 location with a silkscreen marking of HN62408P and the Mask Rom is a TC538200P which is a 42pin 8Mbit (1MB/1024KB) 512Kb Word x 16-Bit/1Mb Word x 8-Bit IC. After searching datasheets for 8Mbit eproms I found that a M27C800 was pin compatible:
So I set my TOP3000 Universal Programmer to IC M27C800 and attempt to read the contents of the P1 Mask ROM and I get an error. Pin 28 (D14) will not read:
This proves that the P1 Mark ROM is faulty. So using the 022-p1.p1 file from out of Mame’s Blue’s Journey ROM (bjourney.zip) I program a M27C800 eprom and solder it into the P1 position on the PCB as a replacement for this fault mask rom:
So let us test it again:
IT BOOTS UP and WORKS! But wait a moment, notice anything? Something is still wrong…
There is sound but some graphics are corrupt:
Before I continue I should explain which ROMS on a MVS cart do what:
Px ROM: Program Data
Vx ROM: Audio Data
M1 ROM: Sound Program
S1 ROM: Static element Data (such as Fonts and UI elements)
Cx ROM: Graphics Data
Because we have good sound and the game is running now, we know that the only ROMS left that could be problematic are the S1 and C1-C4 Mask Roms.
However, all static elements appear to display correctly as you can read the fonts and the High Score screen displays perfectly in its current state:
So we know that it is unlikely there is any problems with the S1 ROM which just leaves us with 4 Graphics Data Roms to check. However it is not possible to check them in circuit so they need to be de-soldered:
Both C1 and C2 are 8Mbit 42pin TC538200P Mask Roms however C3 and C4 are 4Mbit 40pin TC534200P Mask Roms and my programmer doesn’t support them.
Since they are also marked on the silkscreen as HN62408P they should also be pin compatible with a M27C800 eprom and after confirming with the datasheet they do indeed match.
The only caveat being that when I read the 4Mbit Mask ROM as a M27C800 I need to ignore the pin “1” can’t be read error as it doesn’t exist and I get a doubled up 8Mbit file which needs to be split into two 4Mbit chunks by a program such as BINman to be able to compare its CRC with a known good one.
So I read and dump the contents of the 4 Graphic Mask ROMS and find that C4 will not read pin 29 (D15) :
So I now know that C4 is faulty.
I then extracted all the relevant files out of MAME’s Blue’s Journey ROM to compare them with my dumps to confirm they are all good and they all match!
I can now solder back in the mask ROM for C1 to C3 knowing that they are good:
You can test MVS cartridges with missing Graphic ROMS without any issues. The only thing that will happen is that you will have missing graphic tiles and layers from the detached Rom which can be utilised to try to figure out which roms are faulty.
In my case the very last rom I removed (C4) was the one that removed the faulty graphics. It also can look quite funky seeing the game running with missing tiles as tested below with only C1-C3 soldered in:
Since I had no AM27C400 eproms at hand that are pin compatible with the C4 TC534200P mask ROM I instead used another M27C800 eprom to replace the faulty C4.
To do this I extracted the “022-c4.c4” file from out of the Blue’s Journey Mame ROM and then made a copy of it which I then opened in HxDen and then zero filled the entire 4Mbit (512Kb) file and saved this as “4Mbit_Blank.bin” . Then in BINman I merged the two 4Mbit files together to create a 8Mbit file:
I now programmed the resulting file to a M27C800 eprom and then soldered it into the C4 IC position:
Now time to test it again:
While this sort of repair can fix a lot of MVS carts certain games use 64Mbit Mask Rom’s (such as Strikers 1945 Plus) and eprom’s only go up to 32Mbit in size.
This took way too long to write up! Hope you enjoyed the read.