ADDING A FAN TO A C64
 
     The power pack for the C64 is marginal as far as it's power output, but a fan motor
represents a miniscule addition to the load it already sees. There is a source of 12
volts inside the computer, generated by the 9VAC source from the power pack. It was
actually designed to run the cassette motor, but since those are rarely used, it's a good
place to tap off that power. 
     Connect the fan motor across electrolytic capacitor C19, a 2200uF 16 volt tubular,
one of three on the right side of the motherboard. It should be marked on the board. Mine
shows it as the one in the middle, but different runs of PC board may have it in a
different place. The red (+) motor lead goes to capacitor positive, and black (-)  goes
to negative. Tack-solder the leads in place, or just wrap the fan wires around the
capacitor leads tightly, and make sure they don't short to anything else or get pinched
when you put the case back together. It should work just fine.
     You can mount a 2" fan to the top cover, directly over the cartridge port and RF
convertor area (behind the keyboard). There is almost a 1.5" depth clearance back there. 
It's best to space the fan back away from the vents slightly (but not so far back that it
sits on the PC board components). The small vent holes would restrict the fan if it were
to be mounted directly to the case top (unless you're ready to cut a hole in it). If it
were instead mounted on half-inch spacers off the top cover, the fan would simply aid in
normal convection of warm air flow outward. I strongly recommend adding heat sinks to the
chips that normally get hot in the computer: PLA, SID, MPU and (if not already sinked)
the VIC. That will help those chips even more than a fan would. Both would be better
still. If you want the article I wrote concerning installing home-made heat sinks, email
me and I'll send you a copy. 


                                ADDING A FAN TO A 1541

     A fan (internal or external) can be run off the drive's internal power supply. It is
not necessary to disassemble the drive or remove the PC board. You only need to remove
the top cover and the metal shield (if your drive has one) to get to the top of the PC
board.
     As you've noticed, the worst problem of installing a fan is finding the room for it. 
If one is mounted internally, the best you can expect to do is keep the air moving inside
the case and reduce "hot spots". The only kind of fan that would fit inside is the
minature type presently used for IBM microprocessor cooling. They are about 1.5 inches in
diameter and half an inch thick. One could be mounted (with silicon rubber as glue) on
the left side, over the hole in the metal frame (between the case and the frame).
Convection cooling is all there is for the 1541, with or without an internal fan. 
     An external fan can be mounted to the case top to draw warm air up and out, but some
increase in the amount of dust the drive accumulates should be expected. You could run
the fan at reduced speed. In one application, I ran a 12 volt fan off 6 volts to cut down
the noise. It ran at reduced speed, of course, but provided the necessary cooling without
pulling a lot of dust into the unit. Anything that boosts the normal airflow even a
little is beneficial. 
     Most of those little fans run off 12 volts DC at less than 200 mA. See NOTE below! 
You can tie into 12 volts from the 1541 power supply by connecting the fan across C16,
one of the big filter capacitors. It's a 4700uF 16 volt tubular (about 3/4" diam eter and
2" long), the one nearest the heat sink for the regulators. The positive motor wire
(usually red) would go to the positive side of the capacitor (toward the front of the
drive), and the negative lead (usually black) would go to the negative end of the
capacitor or ground. (Note: the metal frame is not a ground). You will not have to remove
the PC board... you can just wrap your wire around the capacitor leads and/or tack-solder
them in place. Don't let your wires short to anything else, and make sure they don't get
"pinched" when you put the drive back together. 

NOTE: make sure the fan you buy runs off 12 volts! If you can only get a 5 volt fan, you
will need to connect it to the 5 volt source in the drive... CR2 anode is a convenient
spot (small diode, near the rear of the drive). Diode polarity is indicated by a black
band around one end... that is the cathode. The anode lead (the one you want) is the
other end. Ground (fan negative wire) goes to the negative end of either one of the two
big filter capacitors. The negative capacitor lead is identified by a black bar on the
capacitor case in the shape of an arrow pointing to the negative end. 


                                ADDING A FAN TO THE SX-64

     There is enough room inside the SX to install a 2" fan. It only involves removing
the top cover. No holes need be drilled in the case, and power is readily available from
the 12 volt source feeding the internal monitor. The idea is to aid the normal convection
of warm air upwards to the outside through the top cover. The fan will be mounted near
(but -not- fastened to) the top cover, in the space between the speaker and the cartridge
port. Since the top cover has many small ventilation holes, you want the fan positioned
at least an inch away from it, and aimed to blow air upwards. If it were up against the
panel, only a small amount of air could flow through a few small holes directly in front
of the fan. I don't know of anyone who wants to drill holes in their SX. 
     If you've never had your SX apart: remove four phillips screws (two on each side
rear) that hold the two long, slender louvered side panels. The panels then slide out to
the rear of the case. That exposes the mounting screws for the top and bottom covers.
Remove the six screws (three on each side) holding the top cover and two more larger ones
at the rear right and left sides near the top... and lift the cover up and off the
computer.
     There are several ways you can mount the fan. I considered glue, making mounting
brackets, etc. Nah. Too much work. I soldered the ends of two pieces of heavy solid buss
wire to the metal shield that surrounds the monitor. With the ends of these wires
sticking upwards, I slid the fan over the wires, poking them through the fans mounting
holes, and bent them over at the top. The wires are stiff enough to hold the fan in
place, and the fan can be easily removed again if necessary. Don't mount the fan too low
in that opening, by the way. Watch out for the black wire that goes to the disk drive
head! If the fan snags it, it will stop the fan and/or chew up the wire. Don't tie the
wire down... it is the cable for the drive head, and it -must- be free to move back and
forth with the head assembly.
     Power for the fan can be taken from a connector at the left edge of the computer.
Locate a two pin connector (white plastic plug and socket about 1 inch long) labeled J1.
The two wires are color coded brown and black... brown is the +12 source and black is
ground. This is the power source for the monitor. The red (+) fan wire goes to the brown
plug wire, and the black (-) fan wire goes to the black plug wire. You can trim off the
insulation a bit on the wires of one of the connectors to attach your fan wires, or just
poke the bared ends of the fan wires into the connector (as long as it makes a good
connection, that's fine). If you trim the insulation from the plug wires to make the
connections, be sure to insulate them with tape so they will not short together or to
any other components. Route any excess wire towards the rear of the computer and tuck it
in the space behind the monitor electronics package.


Ray Carlsen 
CARLSEN ELECTRONICS... a leader in trailing-edge technology. 

Questions or comments are welcome: 
rrcc@u.washington.edu, rcarlsen@i-link-2.net