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 Computing Repair #17: Replace a Broken Power Supply in an Apple II Computer
Introduction I recently posted about purchasing an Apple IIe computer. Shortly after this the RIFA capacitor in the power supply unit (PSU) of my Apple IIe Platinum computer blew in spectacular fashion with load crackles and lots of smelly smoke. I had the computer one for an hour doing a
Read postClean the Heads of an Amiga 1010 Floppy Disk Drive (30-60 mins)
Task: Clean the Heads of an Amiga 1010 Floppy Disk Drive Needed: Q-tip / cotton bud, isopropyl alcohol, screwdrivers Time: 30-60 minutes Introduction All floppy disk drives need to have the drive head cleaned from time to time or they stop working. The drive head is the part that touches
Read postCase Studies in Retro Computing Repair #16: Diagnosing and Fixing an Atari 800XL Booting to the RAM Test
Introduction I recently received a nonworking Atari 800XL that would boot straight to the built-in RAM test instead of the Ready prompt. It failed the RAM test almost completely with a grade of âFâ. I discovered when I cracked it open that it was loaded with cheap Micron Technology (MT) DRAM 64Kx1 RAM chips
Read postCase Studies in Retro Computing Repair #15: Diagnosing and Fixing the Crystal Clock Oscillator Circuit in an Atari 800XL
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 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 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 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 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 (#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 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 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
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