Jul 272019

Some time ago Team Europe has had success in resetting the security fuse on 8751 MCU’s.
See these posts
Post 1
Post 2
Post 3

While looking for something else among my own hoard of stuff I came across an old Choplifter PCB that has been used over the years for parts but the MCU was still present.
Inspired by the work of Team Europe I decided to give it a go myself.
Removing the cap was a bit tricky because I don’t really have the tools required for the task. I ended up using a small file and making a lip so I could fit a screwdriver under it and pry the lid off.

Adding some nail varnish generously donated by my daughter and we have this familiar sight.

I threw it in the UV eraser for 15 minutes and tried reading.
I got data back but was it good?

Comparing to the one currently in MAME I had 1 byte different at address 0x100.
Now, looking at the MAME source we can see that it applies some software patches.

The byte at address 0x100 is indeed on of the patched areas.
Not sure why address 0x27b is also patched. Without this one applied there is no need to compensate by patching address 0x2ff.
Anyway I removed these patches from MAME and booted with my dump and all seems to work just fine. Hopefully the MAME team will agree its a good dump and add it too.

Thanks to Team Europe

 Posted by at 4:18 pm
Jul 262019

This is another ‘poor man’s’ custom IC reproduction I made with no use of CPLD or other complex programmable logics.The part reproduced is the Konami ‘083’, a 28 pin 600 mil in DIP package which most of times comes with scratched-off part name :

It can be found on several Konami PCBs, you can refer to this useful spreadsheet (credits to ‘mattosborn’ on KLOV forums)


As always I observed how its functions were reverse-engineered on bootleg boards and made my own reproduction with simple TTL gates logics :

Final successful testing on a Mega Zone PCB:


 Posted by at 11:05 am
Jul 262019

Received for repair from New Zealand an original Bubble Bobble PCB.Set is made of a CPU board

And a VIDEO board:

It came already adapted to JAMMA so it was just matter to plug it in.I did it but nothing came up on screen. I noticed wires were soldered onto the pins of ‘H’ connector and then a molex connector was used to carry power to JAMMA fingerboard:

I didn’t like this solution because it can cause loose connection so I removed the molex connector and soldered wires directly to JAMMA fingerboard.In this way the board properly booted up, games was perfectly playable with sound too but every alternate horizontal line of graphics was missing :

From top of my experience I know this kind of issue are most of times caused by bad counters (74LS161/163/169).Looking at board I spotted two rows of 74LS169 on bottom VIDEO board:

From schematics I could see they are involved in VIDEO RAM data bus, this made sense :

I went to probe these 74LS169 in circuit with my HP10529A logic comparator, all of them passed the test except the one @IC64 that gave troubles on all its outputs:

I pulled the part out :

It failed the out-of-circuit test on my BK560 :

I installed socket and a fresh IC :

This cured the issue and fixed board completely.End of job.

 Posted by at 10:56 am
Jul 262019

I received from Portugal a couple of Space Invades DX PCBs, a game released in 1994 by Taito (more or less a port of the original Space Invaders, with a few new features).

Both boards were in very good condition but completely dead.Here’s the first one:

All I got on power up was a steady black screen.Probing the 68000 main CPU revealed the address/data busses were active but the three interrupts inputs (IPL0-IPL1-IPL2) were all in fixed high logical state.I traced these inputs back to a PALCE20V8 marked ‘D72-07’ :

Then I disassembled the fusemap of the MAME dump of this PAL being able to identify its inputs and outputs:

/** Inputs **/
Pin 1 = i0;
Pin 2 = i1;
Pin 3 = i2;
Pin 4 = i3;
Pin 5 = i4;
Pin 6 = i5;
Pin 7 = i6;
Pin 8 = i7;
Pin 9 = i8;
Pin 10 = i9;
Pin 11 = i10;
Pin 13 = i12;
Pin 14 = i13;

/** Outputs **/
Pin 15 = o15; /**(Combinatorial, No output feedback, Active low) **/
Pin 16 = o16; /**(Combinatorial, Output feedback output, Active low) **/
Pin 18 = o18; /**(Combinatorial, Output feedback output, Active low) **/
Pin 19 = o19; /**(Combinatorial, Output feedback output, Active low) **/
Pin 20 = o20; /**(Combinatorial, Output feedback output, Active low) **/
Pin 21 = o21; /**(Combinatorial, Output feedback output, Active low) **/
Pin 22 = o22; /**(Combinatorial, No output feedback, Active high) **/

Pin 20-21-22 were outputs to 68000 interrupts lines and they were confirmed to be stuck high along with all other outputs :

Although PAL was secured I tried to read it in my programmer, this would have at least told me the state of ‘health’ of the chip.Reading failed hence the chip was faulty:

I burned a GAL20V8 (GAL and PALCE are most of time interchangeable) with MAME fusemap :

Board booted up with no further issue.First board repaired.


The second board:

As said, it was completely dead.Probing the 68000 main CPU revealed the clock input was stuch high:

I traced it back to a 74F161 @IC51 which acts as a clock divider of the 32Mhz signal generated by the near oscillator :

There was nothing coming from the oscillator into the clock input (pin 2) of this 74F161 counter:

At first glance I thought the oscillator was dead but before replacing it I made a visual inspection on solder side.I found a dry joint on its output pin :

I promptly reflowed it and then powered up the board again.It booted up with no further issues.Double repair accomplished.

 Posted by at 10:34 am