'Fix' Restore Key
Project: Make RESTORE key behave like all the other keys
Target : C64 (not necessary for new boards)
Time : 15 min.
Cost : <1 US$
Use : Never hear the RESTORE key singing
'Killing me softly ...' again.
Replace 'NMI-capacitor' C38 by a 4.7nF one.
The value of the builtin capacitor responsible for triggering
the NMI via the timer 556 is too little (51pF) in
old C64 boards).
On account of the pressure dependant resistance of the keys,
pressing the RESTORE key just as softly as the other keys is not
sufficient for producing a trigger signal at the timer's TRIG
input. Therefore, we will replace it with a 4.7nF capacitor.
The problem described above was fixed in the
new PCBs and in the SX-64.
- Pull off all cables and open case.
- Search for capacitor C38 (51pF) below the leftmost CIA. In
most boards it is built into a resistor case with green base
color! Its color code is: green-brown-black
- Unsolder it and replace it with the 4.7nF one.
- Connect power plug.
- Switch your C-64 on. After the startup screen appeared, press
[RUN/STOP]-[RESTORE] just as softly as you would usually hit the
other keys. Repeat that procedure a few times and if the
RESTORE key seems to behave like the other keys, close the
- Replaced the wrong capacitor. Often the capacitor is built into
a resistor case.
Updated: September 23rd, 1997
Created: February 3rd, 1997
Status : Verified on September 16th
Site copyright © 1997 by Marc-Jano Knopp
This document is part of MJK's Commodore 64 & LCD Page
Brought back to life by Peter Schepers, Dec 10, 2005 because I really liked this site!