Introduction I picked up a Commodore 64 at a Vintage Computer Festival that the seller disclosed had a broken power switch that would not move. I was able to get it at a significant discount hoping that was all that was wrong with it. Fortunately, it was! Case Study Replacement
Read postCase Studies in Retro Computer Repair (#12): Diagnosing and Fixing a Commodore 64 with a Previous Kernel ROM Modification
Introduction I purchased this untested English Commodore 64 from a local friend. Unfortunately, it booted to a black screen and hit my desk for repair. Interestingly, it passed all the diagnostic tests and would boot games from cartridge. However, when booting to BASIC it would yield a black screen. Case
Read postCase Studies in Retro Computer Repair (#11): Diagnosing and Fixing a Commodore 64 with Micron Technologies RAM that Boots to a Black Screen
Introduction I purchased this untested Commodore 64 from a local friend. I was not surprised to find that it booted to a back screen. On the plus side, the machine was clean and in good condition. I detail the repair below along with some comments about a mistake I made.
Read postBuild a 2-in-1 Dead and Diagnostic Test Cartridge for Diagnosing Non-Working Commodore 64s (1-2 hrs)
Task: Build a 2-in-1 Dead and Diagnostic Test Cartridge for Diagnosing Non-Working Commodore 64s Needed: 2-in-1 circuit board, two EEPROM chips, an EEPROM programmer, two 100 nF capacitors, soldering iron, cartridge case and screw(s) Time: 1-2 hours Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from
Read postCase Studies in Retro Computer Repair (#10): Diagnosing and Fixing a Commodore 64 with a Garbled Screen by Reseating the VIC-II Video Chip
Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction I purchased this very nice Commodore 64 off eBay. It was listed as not working and sold for parts. It has a clean 250407 Revision B board and boots to a garbled screen as
Read postCase Studies in Retro Computer Repair (#9): Diagnosing and Fixing a Commodore 64 with Intermittent Black Screen and Nonworking Keyboard by Reflowing Cold Solder Joints
Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction This Commodore 64 with a 250407 Revision B board came in a lot six nonworking computers that I purchased from eBay. This one seemed to boot but was flaky and would sometimes crash or
Read postPurchase an A/V Adapter for the Commodore 64 for Standard S-Video, Composite, and Audio Connectors (5-10 mins)
Task: Purchase an A/V Adapter for the Commodore C64 for Standard S-Video and Audio Connectors Needed: A/V Adapter Time: 5-10 minutes Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction The Commodore 64 comes with either a 5-pin or 8-pin DIN connector for
Read postCase Studies in Retro Computer Repair (#7): Diagnosing and Fixing a Commodore 64 with Wavy Video Output
Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction I purchased this working Commodore 64 326298 Revision A board (1982) with a 5-pin video connector for $100 from a friend. It did indeed work fine when I got it home. However, after it
Read postCase Studies in Retro Computer Repair (#6): Diagnosing and Fixing a Commodore 64 with a Nonworking Socket
Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction This Commodore 64 (250407 Revision A board with 8-pin video din connector) came to me in an eBay lot of six labeled not working. However, it was able to boot and passed all the
Read postCase Studies in Retro Computer Repair (#5): Diagnosing and Fixing a Commodore 64 with Broken Traces
Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction I purchased this nice 250407 Revision C motherboard as part of a lot of boards. It was missing the PLA (U17) and the VIC-II video chip (U19) as shown below. A new GAL-PLA (e.g.
Read postCase Studies in Retro Computer Repair (#4): Diagnosing and Fixing a Commodore 64 with Keys that Don’t Work and no Sound
Introduction This Commodore 64 came in a lot of six I purchased off eBay. All were listed as not working. This c64 booted up just fine but had some key that did not work (e.g. space and return) and had no sound. Otherwise, it seemed like it was in good
Read postCase Studies in Retro Computer Repair (#3): Diagnosing and Fixing a Commodore 64 with No Power
Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. 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
Read postCase Studies in Retro Computer Repair (#2): Diagnosing and Fixing a Commodore 64 with a Bad PLA Resulting in a Black Screen
Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction I purchased a lot of six non-working Commodore 64s from a seller on eBay. I liked the description of the lot because it included the symptoms that each was experiencing. This gave me some
Read postCase Studies in Retro Computer Repair (#1): Diagnosing and Fixing a Commodore 64 with a Bad MOS 7708 Multiplexer Resulting in a Black Screen
Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction I purchased the following Commodore 64 on eBay for $90. The seller said it was not working and had tried to repair it with a GAL PLA. He further said it booted to a
Read postPurchase and Assemble a New Retro Fuzion Case for Your Commodore 64 Breadbin (15-30 mins)
Task: Purchase and Assemble a New Retro Fuzion Case for Your Commodore 64 Breadbin Needed: Retro Fusion Case, Commodore 64 Circuit Board, Philips Screwdriver Time: 15-30 minutes Disclosure: Note that as an eBay Partner Network Affiliate, I may earn from qualifying purchases. Introduction Commodore 64 breadbin cases are notoriously brittle
Read postTroubleshoot a Nonworking Commodore 64 by Testing the Continuity of the Circuit Board Traces (30-60 mins)
Task: Troubleshoot a Nonworking Commodore 64 by Testing the Continuity of the Circuit Board Traces Needed: Multimeter set to continuity mode Time: 30-60 minutes or longer Introduction I recently had a nonworking Commodore 64 with a 250407 board (Rev. C) in a breadbin case that I fixed by replacing a
Read postPurchase and Install an RF Replacement for Your Commodore 64 to Provide S-Video Output (30-60 mins)
Task: Purchase and Install an RF Replacement for Your Commodore 64 to Provide S-Video Output Needed: RF replacement board, desoldering iron, soldering iron, S-video cable Time: 30-60 minutes Introduction The RF module on the Commodore 64 was poorly designed and produces sub-optimal video signals. The Retro Channel has produced and
Read postPurchase and Install a Kawari Replacement for the Commodore 64 VIC-II Video Chip (15-30 mins)
Task: Purchase and Install a Kawari Replacement for the Commodore 64 VIC-II Video Chip Needed: A Kawari VIC-II replacement and a working Commodore 64 Time: 15-30 minutes Introduction The Commodore 64 used a video chip called the VIC-II that was the successor to the VIC chip used in the VIC-20.
Read postReplace a Faulty PLA Chip in a Commodore 64 8-Bit Computer with a PLA20V8 (15-30 mins)
Task: Replace a Faulty PLA Chip in a Commodore 64 with a PLA20V8 Needed: PLA20V8 Time: 15-30 minutes Introduction The Programmable Logic Array or PLA is key to managing the chips using the data bus in the Commodore 64. Unfortunately, the MOS-branded PLAs are prone to failure. The good news
Read postUse Heatsinks to Protect Integrated Circuits Prone to Overheating (10-15 mins)
Task: Use Heatsinks to Protect Integrated Circuits Prone to Overheating Needed: Web Browser, Heatsinks Time: 10-15 minutes Introduction One of the reasons integrated circuits (ICs) fail on retro computers is because they overheat. This is compounded by radio frequency (RF) shielding that can limit ventilation. An easy approach to protecting
Read postExplore the Commodore 64 Pictorial Fault Guide for Troubleshooting a Computer with Problems (10-15 mins)
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
Read postImprove the Sharpness of the Composite Video from a Commodore 64 with a Revision B Circuit Board (30-60 mins)
Task: Improve the Sharpness of the Composite Video from a Commodore 64 with a Revision B Circuit Board Needed: Commodore 64 with Revision B Circuit Board (#250407), Soldering Iron, Clippers Time: 30-60 minutes Introduction The quality of the composite video from Commodore 64 bread bins is not very good. The
Read postPerform a Dead Test on a Non-Working Commodore 64 Computer (10-15 mins)
Task: Perform a Dead Test on a Non-Working Commodore 64 Computer Needed: Dead Test Cartridge or Program, Commodore 64 Time: 10-15 minutes Introduction I have previously posted about using the Diagnostic Test to troubleshoot a non-working Commodore 64. However, there are a number of faults that can prevent this test
Read postPerform a Diagnostic Test on a Non-Working Commodore 64 Computer (10-15 mins)
Task: Perform a Diagnostic Test on a Non-Working Commodore 64 Computer Needed: Diagnostic Test Cartridge or Program, Commodore 64 Time: 10-15 minutes Introduction Nothing is more frustrating than a Commodore 64 that is not functioning properly. Commodore used its own diagnostic software to troubleshoot non-working C64s. This software is available
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