I have no background in electronics or programming. Everything I have learnt over the years has been through self teaching and the help from other kind people willing to lend a hand.

Feb 282019

Some time last year I attended an arcade meet of UKVAC user ‘Bonehead’. It was here that I met up with Virtvic who brought along a couple of boards that needed repair. Among them was this Arkanoid 2 which has had a few attempts of repair by a few different people. Because of this it also came with a list of suspected bad components.
Among the list of suspected dead parts was the Z80 Sub CPU. I tested this and it was indeed dead.
After a quick visual inspection I fired it up and got a “SECURITY ERROR” on screen.
The security error is generated from the sub CPU and is all to do with the MCU which is part of the sub CPU section.
I pulled the ROM and it failed in the programmer with an “OVER CURRENT” error. At this point I was getting suspicious and set about checking other chips on the same busses. Everything on the same bus as the sub cpu was dead. The list includes:

I desoldered and removed them all but I was worried now as the MCU is currently undumped and I wasn’t even sure the game would work even if I replaced all of this.
I fitted a new Z80, RAM, ROM and PAL as I had them on hand. I then set about patching both the main and sub ROM’s in order to bypass security checks and to verify the game worked. It did so I attached the Fluke 9010 to the sub CPU socket and simulated various coin and button presses by writing expected values to the shared RAM.

It was a good start and now I was assured the game would actually work I set about thinking of ways to get around the MCU being dead.
My options were:
-Replace the MCU with a modern one programmed to act similar
-Program my own 8741 from scratch
-Create a PCB to fit in the socket to make necessary connections and bypass certain checks in ROM

I started off attempting to replace it with a more modern ATMEGA MCU. I made up a small adapter PCB which would match the pinout of the 8042.
This didn’t work well at all as the ATMEGA doesn’t have dedicated chip selected lines or any of the other control lines I needed. As a result i scrapped the attempt and decided to start learning 8741 assembly.
I spent quite some time learning the ropes on this one dealing with all its limitations and pouring over the MAME source which simulates this MCU. It really was a great experience for me and I enjoyed it a lot.
Phil Bennett gave me some assistance in setting up a MAME environment to use a real MCU file rather than the simulation and I finally ended up with something that seemed to allow me to boot the game.
I went to test my first attempt but realised that I would need some kind of debounce routine for the coin up processing.

I continued working on the MCU features in the background and started to look at getting hold of the missing chips.
I needed a new Y2203. Without this I have no sound and the game also boots straight into test mode as the Y2203 also processes the DIP’s. For now I was patching this check out too.
Getting the Y2203 was fairly easy and I found one on a scrap board.
I eventually got some 8741 MCU’s for a decent price from eBay and was about ready to test for the first time

Success! Coin up was implemented and buttons were implemented too.
The sticking point was the NEC uPD4701. This handles the spinner inputs and I couldn’t find one anywhere.
Hammy was going to send me one with the next batch of things to dump but Caius came to my rescue sooner and sent me one from a Cabal PCB (thank you Caius and Hammy).
I don’t have any spinners to test controls so I hooked up an Arduino to simulate left and right movement.

From my point of view that’s this PCB fully working. Its taken me months to get to this point but its also been one of the most satisfying things I’ve done in this hobby.

There are some ‘features’ missing from my MCU replacement but I don’t think its anything disastrous. The game no longer caps at 9 credits and the tilt signal doesn’t work within the test mode. There is probably other stuff too but I can work on those if they become a problem. Once it has been tested then I will release it.

 Posted by at 9:07 pm
Feb 282019

I got the same Black Tiger bootleg board back as in my repair log #3.

The sound had stopped working completely.
I did all the usual visual checks and reseating where I could but no joy.
I probed the Z80 CPU and found following a brief flicker at power on the /HALT pin was always asserted. I pulled the ROM and checked it in my programmer but it came back as good. There is nothing in the way of buffering in between the CPU and ROM.
I decided the quickest way to see what was happening here was to attach the logic analyser to the CPU address bus with the trigger set to the /M1 signal.

From here I could see that it started off good but failed when returning from a call. As the return address is pulled from the stack I decided to remove the RAM and test it. This turned out to be faulty reporting that bit 3 had become disconnected.
Replacing the RAM brought the sound back.

 Posted by at 8:42 am

BINman program update

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Jan 022019

Today I’ve uploaded the latest version of my BINman software.
This version is v4.3.2 and has had some rewrites and a few extra features added.
First is the ability to deinterleave the bytes of a file into nibbles.
Second feature added can be found under the “Special” menu. It was added as a request from a user. This swaps the nibble values from one byte and the adjacent byte then deinterleaves that file. For example an original file of: “12 34 AB CD” will output two files, one containing “13 AC”, the other “24 BD”.
Its not something I’ve ever had the need for but obviously someone wanted it so here it is.

As usual it can be found in the “Downloads/PC Software” section.

 Posted by at 7:04 pm

CK2605 Logic Diagram

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Nov 262018

While searching through some documents from Data I/O I came across a bunch of logic diagrams for various PLD’s. One of them was for the CK2605.
As I’ve not seen this in the wild before I thought I’d upload it.

*click the picture for PDF

 Posted by at 6:11 pm
Nov 012018

Some time back I bruteforced the A-17480 PAL16L8 chip from Mortal Kombat II. This was untested until recently when UKVAC member JonHughes tested it and found it didn’t work properly.
We tried several things but always got the same issues so he sent me his full PCB to do some testing of my own.
While I could find anything wrong from an operation point of view I did find that the original TIBPAL16L8-10 PAL chip transitioned states about 4ns faster than the fastest GAL chip I have to hand. I had experimented with GAL’s ranging from 10 to 25ns but the slower ones did just make the issue worse.
In desperation I ordered a NOS TIBPAL16L8-10 from eBay (not too cheap these days) in order to be 100% sure of my work. The result was a perfectly running game.

So what are the issues? Well not a lot really. A GAL substitute will still allow the game to play very well but it did show errors during the POST

The game itself also plays fine but there are some graphical issues here and there, most noticeably on the ground during actual gameplay.
On the video you can see the ground keeps glitching black. This is pretty much the only fault I can see but its definitely worth noting

The video is not the best quality, capturing CRT screens with my phone is never great but hopefully you can see.

 Posted by at 4:50 pm