INSTALLING A FAN IN A C128DCR (USA model in metal case) 11-17-99


            INSTALLING A FAN IN A C128DCR (USA model in metal case)    11-17-99

  INSTALLING A FAN IN A C128DCR (USA model in metal case)    11-17-99

     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. It's easy to blow the dust out with compressed air.
     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 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.
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. 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,
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 C128D must 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.
     The fan and case mounting holes will accept four standard 6x32 by
1.25" long machine screws. 4x40 screws will work if you use washers on the
smaller diameter hardware. 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. 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. 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