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Introduction
I purchased this Commodore 64 with a 250435 board (1984) for $50 at VCF SoCal in 2025. The seller had it labeled as non-working with no information as to the symptoms. I was a bit reluctant to buy this one because the case had some cord burns on it where the power cord had been pressed against for a long time creating a chemical reaction with the plastic that leaves burn-like grooves. However, all the main ICs were socketed, and it did come with one of the better Revision 8 VIC-II video chips. I thought it might make a good parts board if nothing else.
Case Study
My first task was to power this c64 up to see what was wrong with it. Unfortunately, it was completely dead with no power whatsoever. I always use a newly made power supply, so I was sure that was not this issue. Anytime this happens the first thing I try is spraying contact cleaner in the power socket and inserting and removing the power connector several times to create some cleaning friction. I did this and also sprayed the power switch such that the contact cleaner (e.g. WD-40 from Amazon) could get inside the compartment where gunk can build up and prevent contact from being made that is necessary to complete the circuit and turn on the power. I sprayed a generous amount and turned the switch on and off (without the power cable plugged in) about 20 or 30 times to loosen up the contacts. I sprayed a little more and did this again. I plugged in the power cable and was very pleased to see the c64 boot into BASIC! The diagnostic tests all passed, and SID chip sounded pretty good.
Comments
This was an easy fix and a reminder of the power of contact cleaner that has repaired several computers for me including a c64 with a keyboard that wouldn’t work due oxidation and poor contact by the kernel ROM. Unfortunately, the case for this computer should probably be replaced given the chemical burn marks. The keyboard needs a little work and some cleaning. For example, the space bar only works when there is some force. Also, as shown below, this board has one MOS 7712 logic chip in it that should probably be replaced with a 74LS08 as it will likely fail at some point soon. They usually do! This c64 Wiki page has the compatible chip numbers for replacing MOS ICs. I will do these additional repairs when I am ready to finish this up and move it to a good home.
