Received this Mach Breakers PCB from a friend for a repair (it turned out to be an undumped World revision, I alread submitted it to MAME)
Game was released by Namco in 1994 and runs on a powerful hardware platform called ‘NB-2’.Here is ovrview:
- Main CPU: Motorola 68EC020 32-bit processor @ 25 MHz
- Secondary CPUs: C329 + C137
- Custom graphics chips: GFX: 123, 145, 156, C116 – Motion Objects: C355, 187, C347
- Sound CPU: C351
- PCM Sound chip: C352
- Control chip: C16
The board was faulty, most of sprites had jailbars:
Sprites data are stored in ten 16Mbit MASK ROMs (Fujitsu MB8316200B in SOP44 package) located on the MASK ROM daughterboard:
Probing them with a scope didn’t help much since each column of devices has shared address and data busses.So I proceeded in this way.I created some empty binary files (2MByte each one) and loaded them one at a time in MAME in order to reproduce the issue and pinpoint which devices were bad.When I did it for the ones @8A-8B-8C I got pretty same artifacts under emulation:
So I went to remove these MASK ROMs starting from the one @8A of the column :
And I hit it since I was not able to get always same CRC when dumping it so device was really bad.Replacement for the MB8316200 is a Macronix MX29F1610 Flash EEPROM which has same pinout (except for pin 1 and 44 which are used for programming)
Luckily I was able to find among my spares a donor board where to take the devices from :
Time to program it using a SOP44 to DIP adapter:
After soldered it on board I got a big improvement, jailbars were gone away but there were still dots on sprites:
Again I went to corrupt the MAME ROM files and I could pinpoint which was the involved device: the one @4C.I removed it :
I dumped it several times and obtained different CRCs at each reading, it was really bad.As further proof I loaded one of these bad dumps in MAME and I was able to reproduce exactly the issue:
I programmed a new MX29F1610 EEPROM as replacement, this fixed completely the board:
Not only bad TTLs from Fujitsu!
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