Porchy

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.

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
Oct 272018
 

Due to certain things that have been going on elsewhere on the internet I have made the decision to remove the SEGA ROM’s from this site.
I have not personally been asked to take these down but given what I’ve seen happen recently involving SEGA ROM’s and previously with Nintendo too I thought I would play it safe and remove these files.

Sorry for any inconvenience

 Posted by at 7:38 am

Kicker (AKA Shao-lin’s road) (bootleg) repair log

 PCB Repair Logs  Comments Off on Kicker (AKA Shao-lin’s road) (bootleg) repair log
Oct 072018
 

Earlier this year I attended a meetup at UKVAC user Bonehead’s house.
One of the things I brought back with me was an unknown bootleg PCB that a was being given away.
I opted to take this particular PCB because it was 6809 based and I needed something to help me continue work on my Fluke 90 PC software that I started quite some time ago.

This PCB uses the Konami Classic pinout for which I already have an adapter for so following a quick visual check I plugged this in and powered up.

As you can see we have watchdogging going on.
Right next to the 6809 there are two 74LS244 buffer IC’s. A quick continuity check showed that these were connected to the address pins of the 6809.

Probing the 244 at E8 showed that all the outputs were dead. Removing this revealed a broken trace.

At some point in its life there has been a sort here.
I patched the break and fitted a socket and new 244 buffer and checked for shorts before retesting.

Powered up and all was well again.

Confirmed later that the sound is present too and controls are all working.
A quick fix this time.

 Posted by at 5:55 pm

1Mbit EPROM Confusion – JEDEC VS non-JEDEC

 Technical Info  Comments Off on 1Mbit EPROM Confusion – JEDEC VS non-JEDEC
Sep 232018
 

I’m unsure where this all started and who was the first to break the tradition but when it came to the 32 pin 1Mbit EPROM some manufacturers went rogue.
The difference between a JEDEC pinout and a non-JEDEC pinout is two pins swapped. The signals in question are /OE and A16 and the pins are pin 2 and pin 24.

Check out this picture for a visual description

Normally this information would be all we need to know. For example Macronix has the MX27C1000 eprom which has a JEDEC pinout. They also have the MX27C1001 which has a non-JEDEC pinout.
So far so good.

The confusion starts to creep in if you wanted to replace a Macronix MX27C1000 EPROM with say Sony’s CXK27C1000.
Its a natural assumption to make that these two are going to pin compatible but that is where we would be wrong.
Sony’s CXK27C1001 is actually the JEDEC pinout and the CXK27C1000 is the non-JEDEC pinout.

I believe that all manufacturers of the 27C010 use the JEDEC standard pinout.

Here is a table that we have put together that hopefully captures all the variants and their pinout type.

So if your replacing an EPROM of this type then make sure the EPROM you have is the correct pinout or your going to get problems.

Thanks to Caius and Simonden for their help putting the list together.

 Posted by at 10:55 am

Black Tiger repair log #3

 PCB Repair Logs  Comments Off on Black Tiger repair log #3
Jul 012018
 

Although this is a bootleg it follows the original PCB closely.
Couple of easy fixes on this one.
First a character issue and second a sound issue.


As you can see in the video above, the screen is filled with “A”s and none of the text is correct

There is a seperate EPROM used for characters on this game.

Pulling this and reading back with my programmer yielded a valid dump for Black Tiger.
Checking the adjacent associated 74LS273’s and 74LS245 showed I had at least one pin floating.
I traced this back to a nearby TMM2016 which had D7 floating.

Replacing this fixed the screen

The sound issue was even easier. The sound program EPROM was completely smashed. Replacing it fixed the issue.

Job done.

 Posted by at 11:49 am