Caius

Apr 212017
 

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!

 Posted by at 9:19 pm
Apr 202017
 

Got for repair this Neo-Geo conversion cart of Zupapa! a platform released in 1994 only for MVS system and not on the Neo-Geo AES home console :

Most of graphics were blocky:

I opened the cart:

As I said, the cart was a conversion from a donor hardware, this requires the ROMs to be replaced with game code and data plus some other modifications like adding some ICs and jumpers.Doing a visual inspection on work done I found nothing of abnormal until I came across this:

One of the zero Ohm resistors used as jumper required by the conversion was badly soldered.I put it in place and magically all the graphics came back:

A simple but effective fix!

 Posted by at 11:21 pm
Apr 162017
 

Received this Wild West C.O.W. Boys of Moo Mesa PCB for replacing electrolytic capacitors on the infamous ‘054986A’ audio module although sound was still perfectly working :

As usually I opted for tantalum capacitors, this was the final result:

But when testing the PCB I noticed coin input of player 1 was not working, this was confirmed by I/O check which showed this input as stuck:

As workaround somebody put the game into free play:

This is a common issue on the all Konami boards that share the same hardware design.The input signals from JAMMA edge are first routed to some some custom resistor arrays marked ‘005373A’ then to four 74LS257 which multiplex them :

Checking the involved part revealed that input of the 74LS257 @Q3 was almost shorted to ground as well as obviously the output of the resistor array @S15 connected to it:

So the problem was in either of them.Using an audible milliohm meter I was able to locate the point of less resistance with ground in the 74LS257:

So confident I removed the IC:

It failed when tested out-of-circuit:

Replacing it cleared the issue, input was no more stuck.End of job.

 Posted by at 4:22 pm
Apr 112017
 

Bootlegs are worth a repair too especially when they are classic games like this copy of Slap Fight :

PCB was dead, no sign of activity.At a closer inspection, the main crystal which generates the master clock and the 74S04 inverter were missing from video board:

There are several bootlegs of Slap Fight and each one has a different layout and design but looking at online pictures mine was identical to original board.MAME source told me the exact value of the missing quartz :

/* basic machine hardware */
	MCFG_CPU_ADD("maincpu",Z80, XTAL_36MHz/6) // 6MHz
	 


I was not able to find a 36MHz quartz among my spares (it’s not a common value) so had to order it.I got it in few days:

With the correct clock the PCB sprang to life :

Game was playable but sprites and sound were missing at all:

Sprites data are stored in four 27256 located on CPU board.Data lines of these EPROMs are tied to the inputs of four 74LS166 8-bit shift registers:

Probing the components of this circuit I found that the shift load input (pin 15) in common of the four 74LS166 was stuck high.I traced it back to an output (pin 8) of a 74LS32 whose input pin 9 was stuck too.Tracing this back lead me to the cause of the issue:

 Patching the severed trace restored the sprites:

Now the lack of sound.”Listening” with my audio probe the output (pin 5) of the uPC1182 amplifier revealed that sound was present but for some reason it didn’t reach pin 10 partside of the JAMMA edge.A closer inspection revealed a missing electrolytic capacitor (used to filter the output of the amplifier)

I fitted a 1000 uF capacitor as suggested by the typical application circuit of the uPC1182 amplifier:

Another valuable bootleg fixed!

 Posted by at 11:46 pm
Apr 112017
 

Had this bootleg of R-Type (manufactured by Philko) laying around since some time:

On power up board was stuck on this garbage static screen:

Like in the original Irem hardware main CPU is a NEC uPD70116 (a.k.a. V30)

Probing it revealed that the RESET signal (active HIGH on this CPU) was missing, pin 21 was going  LOW on boot with no transition from HIGH state hence no initialization of the CPU itself

But if I manually resetted the CPU by briefly shorting pin 21 to +5V via a 100 Ohm resistor, the board successfully booted and played perfectly:

Traced pin 21 of the CPU back to pin 10 of the uPD71011 whose pin 11 receives the RESET signal and invert it  :

Also the /RESIN input had no initial transition so the problem was upstream.Compared to original hardware the bootlegers semplified the power-ON delay circuit purposely omitting the M51202 voltage comparator (although  there is silkscreening and room for it).They used insted few discrete components like a diode, a resistor and an electrolityc capacitor which actually was not present @C6 (most likely it went detached)

This was the cause of the missing RESET.I fitted a 100uF 16V electrolytic capacitor (after experimented different values) and board booted all the time.Job done.

 

 

 

 

 

 Posted by at 9:58 am