Friday, August 14, 2009

Apple IIc plus 240V modification

I have recently acquired an Apple IIc plus. This is the fastest "stock" Apple II made by Apple Computer. It was only available for a short time, and only sold in the US.

Because of that, they only have a 120v power supply available. I initially plugged it into my 240v to 120v transformer. It's a bit inconvenient (because it is both big and heavy) and I don't really like lugging the transformer around. At first I thought there might be a provision for a switch inside... nope, no such luck. The other option would be to substitute an ATX power supply. Mark referred me to this:

http://www.weirdstuff.com/cgi-bin/item/22157

It looks ok.. and it *might* even fit into the IIc plus case... but it looks more like the size of a IIe power supply.

My intention was to keep everything looking "stock". The power supply had to stay internal with no power bricks, etc. I also considered using James Littlejohn's LittlePower Adapter IIc+:

http://www.reactivemicro.com/product_info.php?cPath=1_28&products_id=150

and placing a picoPSU-60WI and a 12v supply inside, but I am unsure I will be able to fit everything inside. I may reconsider going this route later on if I ever decide to make the IIc plus a truly portable battery-powered computer.

I then did a random google search and found this site:

http://homepage.mac.com/jorgechamorro/a2things/a2c+Web/index.html

Jorge has posted schematic diagrams and how he modified his IIc plus to allow it to be powered directly from the 240v mains.

This is the power supply after I took it out of the IIc plus.

This is the space it used to sit in.

Unfortunately, The replacement capacitor I got was too tall. It would fit just exactly but I did not want the metal shell pressing down on it. So I decided to mount the capacitor sideways

This is the replacement capacitor beside the original one:

This is how it looks mounted:


The electronics shop I get all my parts from (Jaycar) did not have the 20v 5watt zener diodes that Jorge used. I thought that instead of 7 20v ones, I could use 10 15v ones.

7*20v=140v (Jorge's mod)
10*15v=150v (My substitute)

This should give me Vab of 190v (which means I don't really have to replace the capacitor)... But as my luck would have it, they only have 9 remaining units of the 15v zener diodes.

9*15v=135v

Giving me a Vab of 205v.

So I took a pcb and soldered the diodes on the solder side (that way I don't have to worry about insulating the other side from hitting other high voltage stuff). This is how it looked:

Before closing the lid, I cut off a corner of the PCB because the yellow wire is a bit stretched. I also placed a piece of clear tape on the cover in case one of the legs touch the top of the case.

Then I tested it with a multimeter and the voltages looked right (I know. I should not power up a switching power supply with no load... but.. but it's only for a little while). Then hooked it up back to the IIc plus, and it fired up without a problem. (no smoke, nothing)

The unit does get warm in the area near the diodes. I have left it on running a BASIC program drawing random stuff on the hires screen. It's a bit warmer than what I would like but seems to be acceptable. If you do a lot of disk access (continuously cataloging the disk, it tends to get hotter).

Overall I'm happy with the way this turned out. The IIc plus still looks stock on the outside and I'm now able to plug it in anywhere without lugging the oversized transformer around. I have kept the jumper I took off and the capacitor in the event I want to restore it back to default.


1 comment:

Underpants Charleston said...

PSU mods for the win! One of us needs to dig up a photo of Brett's PSU mod on a network switch. PC PSU, made it look like a supercharged dragster switch!