February 11, 2018

Commodore 128 to 64 Power Supply Adapter



A couple of months ago I picked up a boxed C64 breadbin on Craigslist. Got it home and it wouldn't fire up. The LED was dim and it was giving me a black screen. I checked the voltage output on the power supply and it looked ok, so I started looking into possible fixes for this issue and during my tests had the power supply eventually stop giving any voltage at all. It just died. I opened the power supply to find it was one of the resin covered bricks, so basically, it's a goner. I have a few Commodore 128 supplies and learned that they output the correct voltages for a C64 as well. I considered butchering one and making a dedicated C64 supply, but hated to do that, especially if the C64 had enough wrong with it, that it'd be shelved anyway. So... I looked for some ideas online and found a person who actually made an adapter with a C128 female plug on one end and a 7 Pin DIN on the other end that would plug into the power supply and then into the C64. I liked this idea and wrote to the person, but they informed me that they no longer had any of the C128 plugs to use and would need to pull some off dead C128's.

THE IDEA:

So, my quest continued to bring this old C64 to life and I got the idea to wire some sort of connector such as a Female VGA connector to the end of the C128 power supply that could connect to two separate connectors I'd make, one being a Male VGA to 7 Pin DIN (for C64) and the other a Male VGA to 5 Pin C128 plug. This way I could connect either adapter cable to the Female VGA for whichever system I wanted to power. 

I threw the idea past Dale from Dungeon Dwellers Inc during a conversation we were having and he thought it sounded good, but suggested I didn't even need to use 3 connectors and that I could just use a Male & Female 7 Pin DIN connector. This method would allow me to plug the C128 supply directly into the C64 or plug the short Female 7 Pin DIN to 5 Pin adapter in for C128. It was perfect! As they say, two heads are better than one!

GETTING STARTED:

The idea behind this was to cut about a foot long chunk from the end of the C128 power supply, wire a Male 7 Pin DIN connector to the output end of the supply to plug directly into the C64.

Then, taking the chunk I chopped off with the C128 5 Pin plug, wiring on a Female 7 Pin DIN connector that could then be plugged back into the Male end, bringing back my option of powering my C128.

Well, this works fantastic and I'll show you how I did this...

MODDING STEPS:

1. First, I studied over the pinouts for both C64 and C128 connectors to make sure I knew exactly how I was going to wire it all up without blowing anything up.


2. I opened the C128 power supply and double checked continuity from the AC/DC lines to the corresponding pins on my pinout diagram. You only have yourself to blame if you do it incorrectly, right?


Luckily, the C128 supply isn't covered in resin!

You can use these points to double check continuity to the appropriate pins

3. Cut off the C128 plug, leaving about 6-12 inches of wire to work with and separate the wires.

Cutting about a foot from the plug and separating the wires. Make sure you peel back the grounding shield and connect it with the shielding of the new DIN plugs.

4. Peel back the grounding shield and tin each of the 4 wire tips with a bit of solder and solder on the Male 7 Pin DIN in this fashion...

C128 POWER SUPPLY TO 7 PIN DIN (C64):

9VAC (Brown) to Pin 6
9VAC (White) to Pin 7
5VDC (Red) to Pin 5
GND (Black) to Pin 2

Here I show how I had to slice along the seam of the shell to allow for the C128 cable to fit (wasn't pretty, but it worked!)

5. When soldering on the Female 7 Pin DIN, just keep in mind, it's backwards from the Male. As long as you use the pinout above, this shouldn't be a problem.

All finished!

6. After you have both plugs soldered. I'd suggest double checking all your wiring using a multimeter from back inside the power supply and from both the 7 Pin DIN and the 5 Pin C128 end. If testing from the C128 plug, it should be the same as when you started. You only have one shot at doing it correctly without possibly frying your computer! I can't be responsible for any mistakes you might make here.


7. If you did everything correctly, you now have a nifty C128 power supply capable of powering either a C64 or C128! Pretty cool, I'd say!


FINAL THOUGHTS:

After I finished making this adapter, I plugged it directly into the C64 and voila! I was greeted with a bright power LED and lovely blue screen! I must admit, I was shocked it worked without needing a PLA chip, as I had read it's a very common symptom of the Commodore 64 Black Screen.

Not sure how many people are in the same situation as I, wanting to power a C64 using a C128 power supply, but if you are and you'd like to have the option of powering both, this was a $1.59 solution that works great for me!

I'd like to give a special Thank You to Dale from DDI for refining my idea and helping this come to fruition.

Cheers!

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