Random Color Changes and Hang Ups
Symptom: Color changes randomly, often followed by hang ups.
Sometimes only hang ups directly after startup or other
weird behaviour.
Target : C-64 and VC20
Possible sources of failure
Analysis
Note: The following procedures require a multimeter.
Voltage level correct?
Check the 5V supply voltage on pin 1 (GND) and pin 2 (+5V) of
the user port. If you are using alligator clips, you might wish
to use pin A-1 (GND) and B-2 (+5V) of the cassette port, where
the upper and lower side carry the same signals.
If the voltage proves to be in valid range (4.9 to 5.1V), you
should check it over a longer period. If it still seems to be
ok, see section 'Reset problems'.
5V voltage regulator ok?
If you have an old (big) board, check the 5V voltage regulator
located near the control ports. If its output voltage is not ok
(less than 4.9 or more than 5.1V) or if it gets extraordinaryly
hot, replace it.
Power supply ok?
Check the 5V on the power jack. If it is not within the valid
range (4.9 to 5.1V), see section 'Power supply'.
If the 5V show to be ok, it is very likely that the cause for
the low voltage level is the power switch. Impossible, you may
say, but it DOES occur occasionally (twice in our lives), so it
could be a good idea to either rock the switch several dozen
times, open and clean it or to replace it completely.
Color RAM ok?
If you have found the error causing hang ups and the colors
still change randomly, check the Color RAM's 2114 temperature.
If it gets boiling hot, replace it. If not, replace it anyway,
it is not that expensive and it has only 18 pins which makes
clipping off easy.
Updated: May 18th, 1999
Created: February 1997
Status : NOT VERIFIED!
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!