latest updates and/or corrections: 1-16-08

           Included are instructions for the C64, 1541, and SX64
     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. That source 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. C19 is
marked on the board. Note that different versions of the C64 may have the
capacitor in a different place on the board. 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.


     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 to reduce "hot spots". The only
kind of fan that will 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
     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 on 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 (most drives), one of the large filter 
capacitors. Note: that capacitor is marked C52 in very early drives and 
C7 in the 1541C. It's a 4700uF 16 volt tubular, about 3/4" diameter and 
2" long, the one nearest the heat sink for the regulators. The positive 
fan 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 which is identified by a 
black bar on the capacitor case in the shape of a line or arrow pointing 
to its negative end. The metal frame of the drive is -not- a ground. You 
will not have to remove the PC board to make the connections. You can just 
wrap your wires 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: If you can only get a 5 volt fan, you will need to connect it to a 
5 volt source in the drive. A convenient spot is the anode side of a small 
diode CR4 (CR3 in the 1541C only) located 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 and you will 
connect the positive lead (usually red) of the fan to that point. The fan 
negative wire (usually black) goes to the negative end of either one of 
the two big filter capacitors. 


     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 the
wires 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 back of
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 always welcome.


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