PLD Archive news

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Jun 102018

The PLD Archive is currently in the process of being moved to a new wiki.
There may be a delay is adding new files while the wiki get populated. This is currently over half way done but the process is long and tedious bear with us.
In addition to the normal PLD files there is also scope to add more detail and pictures so if anyone has any good quality PCB pictures or extra information like missing PLD IC location details or names then please let us know.

The old table will be kept up for now until we are sure all the detail has been moved over correctly.
You can take a look at the wiki at

 Posted by at 9:18 am

Atari 800xl repair log #2

 Computer Repair Logs, General, Repair Logs  Comments Off on Atari 800xl repair log #2
Jun 022018

Although I grew up with a Commodore 64, I have a soft spot for Atari 8 bit machines. My mission in life is to save them all from going into landfill.

I spotted this grimy Atari 800XL on Gumtree very recently as untested, it came with an Atariwriter Word Processor Cartridge. I met the friendly chap selling the item and we did the exchange for the computer at Town Hall steps, which is a popular meeting place in Sydney.

Taking the machine apart, I was happy to see that the machine was fully socketed and that the PCB was in excellent condition despite it needing a good clean. Actually, I was expecting a fully socketed machine because it was made in Hong Kong just like my 600xl was. Another pleasant surprise was the brand of DRAMs used ( OKI ) instead of the mT variety, which have a bad reputation for reliability and were used extensively in the Atari 8 bit and C64 line.

I had a close friend of mine over after work and we went through the troubleshooting together. Unfortunately, not much happens after power it up. A black screen most of the time and sometimes an intermittent picture, obviously this is a sync issue.

Sometimes I manage to get a screen that looks like this. This is a good sign. At least I know the CPU, ROMs and DRAMs are working to some extent to produce this screen.


Luckily I  have a fully socketed 65XE to swap parts to and from.  I also tried a known semi good GTIA which was bad on one output only but produced a nice clean picture in a working machine. The GTIA is responsible for generating the luminance, color and csync signals to produce an image to the screen.

Replacing it doesn’t change a single thing so I consult the schematics, the signals go directly to a hex non inverting buffer ( 4050 ) so I switch my logic probe to the CMOS setting and start probing the chip. Output 6 ( lum0 ) is good, lum1, 2 and 3 were all bad and all outputs were floating. I wanted to check the CYSNC line (  composite sync ) and that was also floating ( no signal at all  ).

I short the input and output pins of the 4050 ( pins 14 & 15 ) with my logic probe briefly which restores the picture to the screen.

Replacing the chip completes the job!

Now onto the next challenge, cleaning the motherboard and case!

Dogyuun repair log #2

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Mar 212018

Got from Portugal another Dogyuun PCB (after the one of some months ago), this was declared as ‘dead’ by the owner :

And it was so.All I got was a steady black screen, no activity on board, no clock on 68000 main CPU.I checked voltages on edge connector and there was no +5V  so the board was actually not powered :

A quick inspection revealed corrosion on edge connector:

Once cleaned it the board booted and played fine but sound samples were muffled and some static noise was present :

Some sign of electrolytic capacitor leaking was present on sound section :

I fired up my ESR meter and started measuring capacitors.A couple of them, the 220uF 16V @C7 and the 10uF 16V @C9, gave no reading so out of range of my meter (0-99 Ohm)

I replaced them, this restored clear sound.No other issue were found so board 100% fixed.

 Posted by at 5:19 pm

Recreating the Commodore 16 PLA

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Mar 132018

I recently picked up a nice boxed Commodore 16 for not too bad a price.
The PLA found in this is a MOS variant of the PLS100 PLA chip. I don’t believe it can natively be dumped as it seems to have its connection on pin 1 severed internally and decapping done some time ago revealed it was neither a PLS100 or 82S100 device either despite the pinout being the same.

I wanted to make a replacement using the NOS PLS100 chips I have because some people like that sort of thing and there doesn’t seem to be anything out there publically already.

I hooked up the PLA to an Arduino MEGA and wrote a small program to count through all combinations of the address pins and log the outputs to a 64KB binary file.
From here I wrote a program that converted the file to a truth table

and finally into equations which I could compile to a PLS100 fusemap using the old easyABEL program.

From here I could program a blank PLS100 and test in a real machine.

Still need to do some testing but early signs are looking good.

 Posted by at 7:39 pm

Backing up an old BBC Micro cassette tape

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Feb 252018

My friend was wanting to backup an old BBC Micro cassette tape that he believed had a game on it his grandad had made. The tape was marked up as “The Wizards Mountain”

I’d never backed up a cassette tape before and I didn’t even own a tape player anymore.
I originally tried buying a really cheap and nasty portable tape player

This was a total disaster and I kept getting inconsistent reads on various parts but between several reads I had what looked like a complete good read.
Using the ‘BBCTAPEDISC’ program I was able read the data directly from the ‘line-in’ source and it also gave a live update on each block recovered so I could see what was failing.

I originally tried stitching different parts together to make a good file but I just couldn’t get it to work properly so I asked around to see if I could borrow a better tape player. Fairly quickly I ended up with this

This gave me an almost perfect read first time. I ended up with a disc image instead of a tape image but thats fine with me as it loads faster.
The outcome is a text adventure game that appears to have been made with GAC.

Its actually a nice story which I still need to finish once I get some time but we are both really happy to have this saved.

 Posted by at 9:26 am