Task: Explore the Commodore 64 Pictorial Fault Guide for Troubleshooting a Computer with Problems
Needed: Web Browser
Time: 10-15 minutes
Introduction
The best place to start when diagnosing a Commodore 64 that boots to a black or garbled screen is the Pictorial Fault Guide. This web page has amassed countless image examples of the various symptoms people see when their C64 is not working correctly. A really nice feature of the site is that it also provides the root cause of the problem. I used the site successfully a few weeks ago to diagnose an otherwise working circuit board that would boot just fine but with a video signal that would start to get wavy and the progressively worse after being on a for a few minutes. Fortunately, others have seen the same issue and there is a page on the website for this particular fault pointing to a failed 74LS629 voltage-controlled oscillator chip at U31. I was able to desolder mine, solder in a socket, and replace it for $10 with a new one that fixed the problem.
Instructions
Navigate to the Pictorial Fault Guide web site and explore the images and faults.
Below is the image from guide that I recognized as my fault.
Comments
Here is a nice YouTube video from Jan Beta illustrating the process of diagnosing fault using the guide and the diagnostic programs.