INSTALLING A RESET SWITCH ON YOUR C-64 (and C64C) 05-22-99
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 a drill and
soldering iron. The switch momentarily grounds the input to a chip (pin
8 of U20, a 556 timer IC in the C64) which is used to generate a single
reset pulse each 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
