Introduction I friend brought me his Atari 800XL that was not generating any video signal. I confirmed with a multimeter that the chips were all getting good voltages. None of the chips were overly hot, and I confirmed with a working machine that they were all good. Case Study Given
Read postCase Studies in Retro Computer Repair #14: Diagnosing and Fixing a Faulty Non-Maskable Interrupt (NMI) Signal on an Atari 800XL
Introduction I recently received an Atari 800XL from a friend that was booting to a black screen. This required breaking out the oscilloscope to track down the problem. Case Study I started troubleshooting this computer by probing the pins of the 6502 with an oscilloscope after making sure all the chips were
Read postCase Studies in Retro Computer Repair #13: Fixing an Atari 800XL with a Stuck Key
Introduction I purchased this Atari 800XL locally. It was in decent condition and spruced up nicely after some scrubbing with 99% isopropyl alcohol (IPA). I did not know when I bought it whether it worked and was happy to see it boot right up to the Ready prompt with a
Read postCreate a Diagnostic ROM Chip for Your Amiga Computer Using a 27C400 EPROM and a TL866 Programmer with Adapter (30-60 mins)
Task: Create a Diagnostic ROM Chip for Your Amiga Computer Using a 27C400 EPROM and a TL866 Programmer with Adapter Needed: 27C400 EPROM, TL866 Programmer, EPROM adapter, Diagnostic ROM file Time: 30-60 minutes Introduction I have previously posted about building a diagnostic cartridge for diagnosing problematic Commodore 64s. A similar
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 postRepair a Nonworking Retro Computer by Replacing the Motherboard (15-30 mins)
Task: Repair a Nonworking Retro Computer by Replacing the Motherboard Needed: A working motherboard Time: 15-30 minutes Introduction As you have seen from some of my other posts, I have gotten pretty good at diagnosing and repairing 8-bit computers by fixing traces, replacing components, and soldering in new chips. However,
Read postReplace a Faulty SID Sound Chip in a Commodore 64 or 128 With a Newly Made Nano SwinSID (15-30 mins)
Task: Replace a Faulty SID Sound Chip in a Commodore 64 or 128 With a Newly Made Nano SwinSID Needed: Nano SwinSID Time: 15-30 minutes Introduction I have previously posted about the Raspberry Pi Pico-based SIDKick replacement for the SID sound chip found in Commodore 64s and 128s. I recently
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 (#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 postWatch My YouTube Video on the Diagnosis, Repair, and Modification of Vintage Computers (45 mins)
Task: Watch My YouTube Video on the Diagnosis, Repair, and Modification of Vintage Computers Needed: Web browser Time: 45 minutes Introduction I prepared a presentation on the diagnosis, repair, and modification of vintage computers for the Vintage Computer Festival SoCal in 2025 and decided to record it and put it
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 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 postUse a Multichannel Oscilloscope to Test Multiple Pins of an Integrated Circuit Simultaneously (15-30 mins)
Task: Use a Multichannel Oscilloscope to Test Multiple Pins of an Integrated Circuit Simultaneously Needed: Multichannel Oscilloscope with Multiple Probes Time: 15-30 mins Introduction I have previously posted about using an oscilloscope for testing and troubleshooting failed chips such as the 6502 CPU and ANTIC. However, this was done one signal at a
Read postRemove and Replace Batteries from Retro Computers to Prevent Damage to the Circuit Board (10-15 mins)
Task: Remove and Replace Batteries from Retro Computers to Prevent Damage to the Circuit Board Needed: New battery Time: 10-15 minutes Instructions A number of later retro computers included batteries on the circuit board to preserve the Parameter Random Access Memory (PRAM) that stored settings for the monitor, keyboard, and
Read postPurchase Contact Cleaner for Reseating Chips and Cleaning Contacts on Retro Computer Circuit Boards (5-10 mins)
Task: Purchase Contact Cleaner for Reseating Chips and Cleaning Contacts on Retro Computer Circuit Boards Needed: Contact Cleaner Time: 5-10 minutes Introduction I have been posting about tools and technology that can be used to assist with the repair of non-working retro computers. For example, I recently posted about purchasing
Read postPurchase a Hot Air Rework Station for Removing Bad Chips from Retro Computer Circuit Boards (30-60 mins)
Task: Purchase a Hot Air Rework Station for Removing Bad Chips from Retro Computer Circuit Boards Needed: Desoldering Iron, Circuit Board, Hot Air Rework Station Time: 30-60 minutes Introduction I previously posted about purchasing and using a desoldering iron to remove bad chips from Atari circuit boards that are not
Read postPurchase a Desoldering Iron for Removing Bad Chips from Retro Computer Circuit Boards (30-60 mins)
Task: Purchase a Desoldering Iron for Removing Bad Chips from Atari 8-Bit Computer Circuit Boards Needed: Desoldering Iron, Circuit Board, Hot Air Rework Station Time: 30-60 minutes Introduction Repairing retro computers inevitably requires removing and replacing bad chips. Some circuit boards include sockets that make removal easy. The new chip
Read postPurchase an Oscilloscope for Troubleshooting Problematic Retro Computers (30-60 mins)
Task: Purchase an Oscilloscope for Troubleshooting Problematic Retro Computers Needed: An oscilloscope Time: 30-60 minutes Introduction As I reviewed in my previous post about multimeters, I have been learning how to troubleshoot and repair Atari 8-bit computers. Central to this effort is an oscilloscope that can be used to measure
Read postPurchase a Multimeter for Troubleshooting Problematic Retro Computers (15-30 mins)
Task: Purchase a Multimeter for Troubleshooting Problematic Retro Computers Needed: A multimeter Time: 15-30 minutes Introduction It is difficult to collect and use retro computers without developing some repair skills because they do fail. I recently decided to level-up my repair skills and have successfully fixed several Atari 800XLs and
Read postPurchase a Soldering Station for Retro Computer Hardware Projects (10-15 mins)
Task: Purchase a Soldering Station for Retro Computer Hardware Projects Needed: Web browser Time: 10-15 mins Introduction Repairing retro computer will inevitably require soldering. There seem to be two very popular solutions which most people in the community go with. The first is the Weller line. Weller is a German
Read postTest Integrated Circuits Using a TL866 Universal Programmer (10-15 mins)
Task: Test Integrated Circuits Using a TL866 Universal Programmer Needed: Web browser, TL866 Universal Programmer, Compatible IC to Test Time: 10-15 minutes Introduction Troubleshooting a failed retrocomputer can often come down to determining whether any of the integrated circuits (ICs) have shorted and failed. There are several options for testing
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
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