INSTALLING A FAN IN A C128D (metal case C128DCR)   1-18-98

     Although there is a place cut and drilled for a fan on the inside rear
panel of the metal-cased C128D, few were actually 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 D 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 easy to blow the dust out with compressed air at a gas station if you
don't have an air pump at home. 
     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 out. 
     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 
Questions and comments are welcome! 
email: rrcc@u.washington.edu or rcarlsen@i-link-2.net
hten 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 
Questions and comments are welcome! 
email: rrcc@u.washington.edu or rcarlsen@i-link-2.net
re 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 
Questions and comments are welcome! 
email: rrcc@u.washington.edu or rcarlsen@i-link-2.net
 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 
Questions and comments are welcome! 
email: rrcc@u.washington.edu or rcarlsen@i-link-2.net