Porchy

Atari 2600 ‘Woody’ composite mod

Mar 132012

Stiggy gave me an Atari 2600 he had going spare when he came round.
Ive never owned one before but its always been on my list.

The old 2600 only has RF out which is completely rubbish on modern TV’s so it was off to the internet to see what kind of mods exist.
After a short while of checking different sites I came to the conclusion that there is no decent, definative guide for my version of 2600.
My mainboard seemed to be a little different in layout than what the guides were based on.

Looking at the other guides they show that the video signals all come from one IC which is standard across all the 2600 models so I traced out the SYNC, LUMA0, LUMA1, LUMA2 and COLOUR signals myself and ran some wires from the points and to the outside world.

As you will see, there is a “COLOUR” label with thats crossed out. This is because I originally followed the circuit through the resistor where I should have followed it from the resistor up to and through the capacitor above it. I ended up tapping into a +5v line by making this mistake so ended up with no signal at all.

I made a quick design in EagleCAD and etched a board based on a simple transistor based amplifier running the LUMA signals through various size resistors.
After taking my +5v from the nearby voltage regulator, fixing my mistake that I highlighted earlier and doing a test with a loaned Harmony cartridge I saw a fairly decent image on screen. Its a little dark and this can probably be changed with fine tuning some resistor values but this will be more than acceptable for me.

The pictures don’t look too impressive on the photos but they are a joy compared to RF.
Ive yet to hook the sound up but the wire is there for it, this will be tomorrows job along with properly fitting the phono plugs.

EDIT: Sound is now hooked up and fully working. All phono sockets are fitted. What a nice mod it was.

Virtual Boy repair log #2

Mar 112012

As with all VB’s and in my previous repair, one of the screens goes a little strange, in my case it was the left screen.
I initially used the oven fix method which worked well but only for a short amount of time.

I fired it up today and was greeted with the same left screen showing garbage.
Rather than use the oven trick again I decided it was time to try one of the more adventurous methods out there.
Turns out there is a nice video on YouTube of how to fix it using a soldering method.

Instead of dropping a load of solder onto it I used some liquid flux and a small amount of solder. You can see it working quite easily and no braid was needed to mop up the excess.

The whole thing only took a few minutes and worked perfectly when I put it back together.
Time will tell how long this lasts but I don’t see why it should cause issues again.

SEGA Master System repair log #2

Console Repair Logs, Repair Logs 1 Response »

Mar 102012

Stiggy dropped round today for a cuppa and brought his sick Master System with him. I have 2 of the mark 1 MS units so we did a swap.
Basically this system was always seeing the UP direction pressed on port 1 even with no controller connected.
Looking at the schematics it would appear that the custom IC 315-5237 has an internal pull-up resistance on each pin and the controller grounds this to register a button press. As I found the pin giving out a permanent low signal chances are something has gone wrong internally.
What I did was fit a resistor between this pin and VCC which changes the default state to a logic HIGH but will still allow the controller to drive it LOW for the button press. Almost certainly not the ideal way of doing it but I don’t know the MS very well at all so this will have to do.
The system now works perfectly. This MS also has a couple of built in games which my old one didn’t.

Commodore Amiga Phoenix PCB PALs/GALs

PAL Updates Comments Off

Mar 102012

During my random internet searches I came across some PAL dumps for a rare version of an Amiga 1000 motherboard.
I still don’t know completely what this board does over an original.

After contacting a few people from the forums asking for permission to offer these up for download I was given the name Andrew J Wilson who is the developer of the board.
I cant seem to find this guy to ask his permission so, Andrew if you ever read this and aren’t happy with me hosting them just let me know.
The files are in a .zip file and there is also a dump of the SCSI controller EPROM in there.

Thanks to jopower from the a1k.org forums and DonutKing from Vintage-Computer.com forums for their help.

Jumping repair log #2

PCB Repair Logs, Repair Logs Comments Off

Mar 042012

As mentioned in a previous post, when I converted my Jumping board to Rainbow Islands I noticed that all the text in game was black. Going back through some pictures I took when I first got the board I see its present there too.

So where do I start?
I know from making my conversion that the palette values are stored in the program ROMs and they are pushed out to the palette RAM at address 200000.
I looked at the RAM with a scope and all seemed fine plus all the other colours seemed fine.
I also know that all the values required for this text colour is when the 2 least significant bits (A0 and A1) are active, so I traced these out down to the video board.

After a long session of following various signals I came across a 74LS374 chip.

This had all its inputs stuck low but according the the scope had a fair bit of noise on them, enough noise in fact to make my logic probe see it as pulsing HIGH/LOW. Following these inputs over to the chip next door I see a 74LS273 with its outputs giving off this crazy signal.
I replaced the 74273 and booted the game

If you look carefully you can see the lower part of the text is missing and a bit scrambled. Taking another look at that 74374 chip and its outputs are still crazy despite having good inputs. After a quick desolder and replacment I got this

All fixed and now my conversion is totally complete.
I have left one bit of graphics the same as the Jumping. If you play the game, in the lower left corner, you number of current lives is displayed as blue stars. On the original these are small rainbows. Just a note in case I ever release my modified files and someone tries to sell it as an original or something.

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