Adding a cooling fan to the Commodore 128DCR

Call it a "refurb weekend sequel" to our previous work on my beloved Commodore 128DCR. It's been a hot, horrid summer in Floodgap Very Sub-Orbital Headquarters and I was somewhat concerned about the heat in the house computer lab even with the A/C cranked up to "Vegas weekend for Southern California Edison's Board of Directors" levels. But it's even worse for cooling when your one and only rear vent looks like this:

(No, I don't know what spilled there either.) The European plastic-case 128D (not this metal-cased "D Cost Reduced") has a cooling fan — and I recently landed an Australian one, more on that later — but as part of becoming CR the fan was eliminated, relying entirely on that vent and whatever warm air comes out of the rear ports to save the 8502 from being "well done." Fortunately Commodore determined it was also too much C to remove the mounting holes, so let's put in a fan instead of hoping the convection cooling is good enough.

Although even now most 128DCRs don't have one, adding a fan historically isn't a very rare modification, enough so that there are some general recommendations. Since most 5V fans won't generate enough airflow with that vent baffle in the way, the usual advice is a 12V unit. The mounting holes will fit a standard 60mm PC case fan; I selected an off-the-shelf 60x60x10mm unit but there is enough room for something thicker. For the details on cracking open the case and getting the power supply out, see the prior post.

We have several options to power the fan. There are solder points you can connect to on the top of the board and some people have even tapped the points and traces on the underside, though that requires removing the board the power supply sits on. The easiest in this case (and the way recommended by Ray Carlsen, Commodore repair demigod) was to get it directly from the power supply wires just as they exit into the board power connector, since happily there was enough exposed metal that I could solder directly to them. The yellow wire is +12V DC and you can use either of the ground lines. I put on a connector here to make replacing the fan later more straightforward, checked voltage and polarity, and then plugged in the fan.

The next question is mounting. Many folks use bolts, but other than when the disk drive is running, the 128 is a silent machine and I didn't want a rattle on top of the fan noise. The anti-vibration silicone mounting pins usually used in silent PC setups will sort of fit, but the normal approach to insert them in the back and pull them through doesn't fit with the 128 mounting holes.

After dithering over drilling the holes out a little wider, I decided instead to install the pins in reverse and pull the tip of the pin out the back.

This fit, but the downside of doing it this way is that, with the fan's airflow pointing out the back, the fan will have a tendency to push itself away from the mounting bracket. If you use long pins as I have here, though, you can sandwich them between the case and the power supply bracket. This not only keeps the fan in place but also allows the pin tails to serve as a handy gasket for further sound deadening.

With the fan installed, I used a small hook to pull the tails up and clear of the airway at the same time I screwed back in the rear mounting screws next to it so that the pin tails were firmly pinched in place. Make sure you don't bend the power supply bracket in the process.

Installed, with the fan cable looped out of the way. (Remember: the power supply connector is not keyed. Ensure the white wire on the connector is closest to the front of the machine or you'll let out the magic smoke.) I never had a thermometer on it before, so I can't say how much of a difference it's making, but air is moving and it's still a pretty quiet machine. You can never have too much insurance with these things.