INSTALLING A RESET SWITCH ON YOUR C-64 (and C64C)

     You don't really need a schematic... I can talk you through it. You need a momentary
contact pushbutton switch (available from Radio Shack), a few lengths of wire and some
hand tools, including drill and soldering iron. The switch momentarily grounds the input
to a chip (pin 8 of U20, a 556 timer IC) which is used to generate a reset pulse every
time the computer is turned on.
     Connect one side of the switch to the junction of capacitor C105 (a 0.1uF disk
ceramic), resistor R50 (a 1 meg 1/2 watt), and pin 8 of the IC. NOTE: C105 is C34 in some
versions of the 64. It's easiest to tack-solder onto the resistor leg nearest the
capacitor on the top of the PC board. You don't have to pull the board out of the case.
The other side of the switch goes to the nearest ground foil, found at the edge of the PC
board near the resistor. By the way, don't mess up and connect to the far side of the
resistor... that goes directly to the +5 volt supply! Grounding that line will kill
chips! Want to make the modification fail-safe? Add a 100 ohm 1/4 or 1/2 watt resistor in
line (in series) with the switch. Then if you make a mistake, it will do no harm... it
just will not work.
     With the proper lengths of wire, you can mount the push button anywhere it will fit
on the case. I like to install it on the lower left side near where the wires connect to
the PC board. If mounted to the lower cabinet half-shell, the wires will not be disturbed
when the keyboard (top half shell) is removed/installed. Drill the appropriate sized hole
for the push button and mount it so that it doesn't touch the PC board and cause a short.
Solder the wires and you're done. Solder quickly, by the way... those little switches are
plastic and melt from too much heat. 
                    
                      A RESET SWITCH FOR THE C64C
     
     You must remove the metal shield (heatsink) from the top of the board to get to the
junction of capacitor C43, the anode of diode CR5, and pin 5 of IC U23. Tack solder one
wire of your added pushbutton to pin 5 of the chip... it's the only available connection
site without removing the PC board. The other side of the added switch is connected to
ground. Again, for safety's sake, it's advisable to install a 100 ohm 1/4 or 1/2 watt
resistor in series (in-line with one wire) with the push button switch.
     Mounting the switch in a C is a bit tricky. You must prevent the switch terminals
touching the shield when it is reinstalled. Bend the shield or cut a small portion of it
away if necessary to avoid a short circuit. When reinstalling the shield, make sure the
little fingers touch all the chips. It is a heat sink and helps to lengthen the life of
those precious ICs. If necessary, bend down all the tabs slightly before installing the
shield.

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