17 Oct 2018

Sega 837-6443 - System 24 FD controller reproduction

Floppy based games on System 24 are becoming incredibly hard to find, not that rom based games are easy... but at least way cheaper, probably cause they are crappy Mah-jong or Quiz games in Japanese.

I designed a reproduction of the floppy drive controller so anyone with a rom based game can enjoy floppy based games:



It's a 1:1 replacement, same dimensions, same layout and fits in place of the OG one. And it works just great :






10 Oct 2018

Act Fancer - Data East 1989 (repair log)

This board was given to me as faulty in a deal.


Upon power up game was stuck on a garbage screen:


I quickly noticed work RAMs were shiny ones (known to have a high failure rate) but I dumped the 3 program ROMs first: they matched the Japanese rev.1 romset in MAME. Probing the RAMs didn't revealed anything weird but by using the oscilloscope I could "see" main CPU was sending data cyclically. Cleary no valid code was executed and CPU was stuck in a loop. I pulled both work RAMs and both tested bad on my programmer. After replacement game booted mostly fine, with sound, texts and background but sprites were replaced by big misplaced blocks of garbage:



Again I pulled and dumped the 8 sprites ROMs but they all matched. RAMs didn't show anything weird either so I started probing the TTL around and noticed one of the inputs of the LS10 @J4 was stuck low. Being a triple NAND gate it meant the associated output was also stuck (high this time = NAND). I tracked the signal to the Q output of one of the latches of the LS74 @J1. All inputs were correct with activity where it should be but outputs Q and /Q were just stuck. Piggybacking a new LS74 chip on top of the suspected faulty one cleared the issue. I replaced it and sprites were fully back:



Game fixed.

3 Oct 2018

Sega 834-6510 I/O board reproduction - part 2

This time I received the blank PCBs.
As you can see layout is identical to the OG one:




Side by side comparison once assembled:









26 Sep 2018

Mutant Fighter - Data East 1991 (repair log)

Game took very long time to boot, then would play extremely slow, sometimes hanged, sometimes played overspeed for a second, and also had no sound. Otherwise board was in very good condition like it's never been operated:


I started by troubleshooting sound issue. First obvious thing I noticed was sound RAM @ J24 was a shiny one. Piggybacking a known good RAM on top of it restored sound. I replaced it and that was all that was needed in the sound section.

Then the second issue regarding speed of play, hanging, overspeed. Quite weird. I probed main CPU (68000 CPU in a custom QFP package marked '59') for a dodgy RESET or CLOCK signal: nothing to mention here. Then I found by touching a specific area of the board on the solder side I could get the game to play at correct speed for a second, and by doing so every second I could have the game playing normally. I thoroughly inspected the area and found a factory defect: one of the leg of the LS74 @ K3 wasn't soldered. I had the impression that by applying pressure on it game would play fine.


I resoldered it but nothing changed. Thinking the chip could be bad and not having the possibility to test it on board with my logic comparator because of it being SMD, I took the decision to replace it: no dice.
To me there was clearly a floating signal somewhere and by touching the concerned trace/pin with my hand I could restore the connection or at least drive the signal to a state where the board would be happy with it. I quickly found a floating trace, that lead me to an other LS74 @ J5. This time chips seemed soldered properly but by using my magnifying lamp I could see one of its legs was covered in solder, so as the associated pad but there was a really tiny crack in between. I tried to reflow the leg but solder was stubborn and didn't want to adhere to it. I had to add quite a big blob of solder for it to adhere on both the leg and the pad:


This time game played normally:



Game fixed.


21 Sep 2018

Sega System C2 multi kit - part 2

After assembly it was time to test the boards I routed:



Before installation ROMs IC4/IC31/IC32/IC33/IC34 must be pulled and jumpers JP5/JP7/JP17/JP18/JP19/JP20 must be set to 2-1.


The 2 boards fit like this:



Program (& graphics) romboard:




Sound romboard:






Interconnection:




Et voilà!




Everything works as expected!




12 Sep 2018

Neo Geo AES - SNK (repair log)

This console has been donated to me (well I had to pay shipping from the US which was huge!) as not working after a failed BIOS mod. I've seen failed BIOS mods before but that one was awful...
The person who attempted it for sure didn't have the appropriate tools and after what I think was a long struggle, managed to pull the original BIOS, ripping many traces in the process. Then, as holes weren't cleared properly, they chose to solder wires between the motherboard and a DIP40 socket:


And tried to patch some broken traces on the solder side too:


After realising it was a complete fail the board was used as a donor, one of the work RAMs has been pulled, and of course a pad has been ripped and few others lifted:


Admitedly I was quite disapointed. I cleaned the case the best I could and sent the motherboard to the scrap pile.
Many days later I went back to it, long story short and as suprising as it seems, I don't own an AES anymore so I found motivation to accept the challenge.
First, and out of curiosity, I checked the patching wires: 70% were good, 20% were absent, 10% were wrong.
I removed the bodge, cleaned the area a bit and cleared the holes:



I installed a socket:


Did the trace patching work on the solder side:


Then installed a new work RAM and patched the missing pad (incredibly other lifted pads survived the soldering):


Finally installed a UniBIOS (V3.3). It looks much better now:


All connections in the BIOS area checked good, so as work RAMs.
Time for a test.
We have a Neo Geo splash screen with the jingle playing!


Title screen of the game (sorry, only cart I have):


Everything works as it should (graphics, sound, controls):


Console fixed!

6 Sep 2018

Sega System C2 multi kit - part 1

After having hacked all Sega System C2 games to bypass security protections I had the idea of designing a kit to support all the games on a single motherboard.

As System C games (3 of them) are fully supported on System C2 I also included them.

That's a total of 14 known different games (plus 3 vending machine romsets, not really games so not included):
- Bloxeed (System C)
- Borench (System C2)
- Columns (System C)
- Columns II (System C)
- Ichidant-R (System C2)
- Poto Poto (System C2)
- Puyo Puyo (System C2)
- Puyo Puyo 2 (System C2)
- Ribbit! (System C2)
- Stack Columns (System C2)
- Tant-R (System C2)
- Thunder Force AC (System C2)
- Twin Squash (original rotary stick version) (System C2)
- Zunzunkyou no yabou (System C2)
And I also added my Twin Squash hack:
- Twin Squash (joystick hack) (System C2)

I went for a very simple approach: big EPROMs with bank switching logic and game selection by dipswitches (a header connector for connection of a remote dipbank is also included).
The System uses 2 independent ROM banks:
- one for CPU code, graphics and music
- one for sound samples
Then I drew the schematics and assembled a prototype (of course it was a bit messy with hundreds of jumper wires).
Due to the C2 board layout I designed 2 boards interconnected with jumper wires:


And tested all the games successfully:















At that point I was very satisfied by the results and decided to route PCBs:



Which came in the mail few weeks later:




Stay tuned for the next part ;)