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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


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

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!