INSTALLING A FAN IN A C-128DCR

Ed.note: This article was authored by Ray Carlsen, who is well-known in electronic circles for his skill in bringing dead Commodore hardware back to life.  Don't hesitate to contact him if your C= machine goes belly-up on you, as his rates are quite reasonable.  I reformatted this article for easier reading, added some information about fan types and sources, and added some photos of a C-128D with a cooling fan installed.

Although there is a place cut and drilled for a fan on the inside rear panel of the metal-cased C128D, few (if any) were sold with the fan installed. The benefits of forced-air cooling should make it a priority for anyone who owns one of those models to install a fan.  Unlike the "flat" C128, the DCR doesn't have the metal shield that touches the chips to draw the heat away, so convection cooling is all there is. The box was designed for the fan to pull air through the front of the computer (vent holes in the lower front panel), over the chips and out through the rear panel opening.

Fans are usually marked with two arrows to indicate the directions of rotation and airflow.  If your fan is not marked, a temporary hookup to the fan will tell you "which way the wind blows".  You want it directed out the back of the computer. Since the case was designed that way, the effect of drawing air out of the computer case has a minimal effect of drawing dust into the internal disk drive.  Still, it's a good idea to check it at least every six months, and more often if you live in a very dusty area (Ed.note: or if you keep pets in your home).  It's easy to blow the dust out with compressed air.  (Ed. note: by "compressed air," it is meant the stuff you buy in cans at the local computer store, not what comes out of an air compressor.)

Since the C128D's internal power supply puts out both +5 volts and +12 volts DC, either of those voltages could be used for a fan.  Although a 120VAC type would work as well as a low voltage one, I couldn't find any 120 volt fans that small, and the 5 volt versions are more expensive.  Connecting any of the three types of fans to the computer is easy.  You only need to know where to tap off the power.  I'll give you instructions for connecting a 12 volt fan since it's the most common type and is readily available.

The maximum size of the [fan] opening is 2.5" high by 2.5" wide by 1.5"deep.  The spacing of the four mounting holes is exactly 2" center to center.  A "standard" fan case size is 2.36" square by about an inch deep (Ed. note: the fan being described is a 60 millimeter fan, similar to the types used on CPU coolers in modern PCs).  It makes sense to buy a fan that exactly fits, rather than trying to modify the opening for something else.

Mouser Electronics 1-800-346-6873) has three fans that will fit the opening: part numbers 432-31432, 432-31434, and 432-31436 at $12 each.  They are all 12 volt ball bearing models and differ only in the amount of air they move (called CFM, or cubic feet per minute).  The higher (part) number is the higher CFM rating, by the way.  Of course the faster the air flow, the noiser the fan, but because of where it's mounted, noise shouldn't be a problem.  You'll get used to a bit of noise if you know it's cooling those precious chips!  Mouser has a web page for those interested: www.mouser.com.  They are an industrial supplier and maintain a good stock of parts, so you shouldn't have to wait long for your order.

Allied Electronics Inc. @ 1-800-433-5700 is another outlet that has a good selection of suitable fans that range in price from $8.50 to $20. Their web page is: www.allied.avnet.com. They have more than a hundred outlets nationwide, so you might find one near you.  Some fan part numbers from their catalog: 592-0750, 592-0760, 592-0770 selling for $8.50 each.  Note that the -lower- numbers are for the higher CFM (and noise) rating.  Low cost fans are sleeve types rather than ball bearings, but even the "cheapies" will last for many years (Ed. note: true to some extent, but they will get noisier as they age).  Ball bearing equivalents of the above numbers are: 592-0690, 592-0700, 592-0710 selling for $11 each.  Here again, the lower numbers are the higher CFM and noise rating fans.  Allied Electronics also has a pretty good selection of standard and mini DIN plugs used in Commodore computers.

Jameco Electronics @ 1-800-831-4242 (www.jameco.com) also sells fans, and has a small selection of Commodore IC chips available as well.  I counted seven fans in their latest catalog that would fit the 128D case that sell for under $10 each, such as: part number 75352 for $7.95.  If you want to order one, what you need to specify is: 2.36" square (Ed. note: 60mm), 12 volts DC, the type of bearings (ball or sleeve), and the CFM rating.

I would go with the highest CFM rating to get the most cooling.  The noise only reminds me that it's working!  Most fans have 12" lead wires, but some will come with only 5" of wire, so you may have to "pigtail" extra wire to make it reach...no big deal.  Insulate any bare wires to keep them from shorting to each other or anything else.

The cover of the C128Dmust be removed to do the fan installation.  Remove two screws along the side bottom front edges and three more on the sides and top of the rear panel.  The top cover must then be slid back about 3/4" and lifted up and off.  (Ed. note: it may be necessary to use a small blade screwdriver to pry the cover back enough to disengage it from the chassis.)

The fan and case mounting holes will accept four standard 6-32 by 1.25" long machine screws.  4-40 screws will work if you use washers on the smaller diameter hardware (Ed. note: not recommended).  Don't overtighten the screws or it could damage the plastic fan housing.  A dab of glue on the screw threads will keep them from loosening up over time.

Mounting the fan with screws and nuts requires that you first remove the power supply from the 128D.  As an alternative, a thin bead of silicon rubber sealer can be used to"glue" the fan in place, and you will not need mounting hardware or need to remove the power supply (Ed. note: again, not recommended). Silicon rubber takes about an hour to "set up" and is fully "cured" in about 24 hours.  Don't get any sealer on the blades or it may cause the fan to stall, or vibrate from the imbalance.

To connect the fan to the power supply 12 volt DC source: locate the short wire bundle that goes between the power supply and the motherboard.  There are six wires in that bundle.  The brown and white wires are the 9VAC, the red wire is +5 volts, the two black wires are ground, and lastly, the yellow wire is +12 volts DC...the one you want for the fan.

The polarity of the fan hookup is important.  Most fans come with two wires, one black (-) and one red (+).  Connect the red fan wire to the yellow wire of the C128D power supply, and the black fan wire to either of the black power supply wires.  You can pull back the insulation a bit on the power supply wires (or trim a little insulation away with a knife) and just wrap the bare ends of the fan wires around them if you want.  If you make a good electrical and mechanical connection, you don't need to solder it.

Ed.note: there are two holes in the power supply printed circuit board immediately adjacent to where the above-mentioned wires are connected.  These holes can be used to connect the fan wiring.  Use a solder sucker to clear solder from the holes, strip about a 1/4 inch of insulation from the fan wires, insert them into the holes and solder.  Examine the underside of the board to determine which hole goes to +and -.  Remember: the YELLOW wire is positive.

Make sure your added wires don't short to each other or any other wires or metal.  Wrap electrical tape around exposed wiring if necessary.  If you unplug the power supply from the motherboard for any reason, make sure you get it back in the right way.  If you reverse it, you will damage the computer.  Note that one black wire of the bundle goes to pin 1 of socket CN7 on the motherboard...pins 1 and 6 are marked on that board.

Ray Carlsen CET
Carlsen Electronics

Ed.note: I've attached two pictures taken of my C-128D after installing a cooling fan into the power supply.  The fan I used was an Antec 60mm case fan, UPC number 761345760065.  To attach the fan to the power supply subchassis, I enlarged the fan mounting holes with a 3/16 inch drill and used the self-tapping mounting screws provided with the fan.  Also note how I made the electrical connection, which arrangement allows the fan to be replaced without having to unsolder any leads.  Go to Antec's website for more information on this fan.

     Thank you for taking the original article and enhancing it with helpful editorial notes.

          Truly,
          Robert Bernardo
          Fresno Commodore User Group
          http://videocam.net.au/fcug
          The Other Group of Amigoids
          http://www.calweb.com/~rabel1/
          Southern California Commodore & Amiga Network
          http://www.sccaners.org

Sweet!  Which reminds me that I should have Ray Carlsen install a modern power supply in my C128DCR.

Truly,
Robert Bernardo
Fresno Commodore User Group - http://www.dickestel.com/fcug.htm
Southern California Commodore & Amiga Network - http://www.portcommodore.com/sccan

Quote from: RobertB on October 21, 2024, 03:55 PMSweet!  Which reminds me that I should have Ray Carlsen install a modern power supply in my C128DCR.

I thought Ray had retired from working on C= hardware.

Ray still manufactures his power supplies and video cables.  https://portcommodore.com/rcarlsen/customPS.html  In fact, I bought a VIC-20CR/C64 mini power supply and a custom a/v cable from him today when I visited his house.

Truly,
Robert Bernardo
Fresno Commodore User Group - http://www.dickestel.com/fcug.htm
Southern California Commodore & Amiga Network - http://www.portcommodore.com/sccan