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Five bad Commodore 64s. One hour. All fixed!

Adrian's Digital Basement・54 minutes read

Adrian repairs five broken Commodore 64C machines in his digital basement, using troubleshooting tools like an oscilloscope to diagnose issues like faulty DRAM chips and CIA 6526 chips, ultimately restoring functionality to all machines. The repair process uncovers various issues like dirty keyboards, faulty chips, and potential manufacturing defects, highlighting the reliability of the Commodore 64C despite these challenges.

Insights

  • Adrian successfully repairs five broken Commodore 64C machines in his digital basement, showcasing his troubleshooting skills and knowledge of vintage computing hardware.
  • The machines' issues range from faulty DRAM chips, dirty keyboards, to malfunctioning CIA 6526 chips, highlighting the complexity and diversity of problems that can arise in restoring vintage computers, ultimately emphasizing the importance of thorough diagnostics and component replacement in achieving successful repairs.

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Recent questions

  • How does Adrian troubleshoot his broken Commodore 64C machines?

    Adrian uses tools like an oscilloscope, diagnostic cartridge, and reliable power supply to diagnose issues. He tests video output and power supply functionality with a ZIF64 machine.

  • What common issues does Adrian encounter with the broken machines?

    Adrian faces problems like faulty DRAM chips causing black screens, dirty keyboards affecting typing, and faulty CIA chips impacting functionality.

  • What components are crucial for the Commodore 64C's functionality?

    Components like the CPU, Sid chip, vic2, and clock synthesizer are essential. The 6526 chip is crucial, with alternatives like 6522 or 6520 not compatible.

  • How does Adrian identify faulty parts in the machines?

    Adrian uses diagnostic tools like a dead test cartridge, oscilloscope probe, and diagnostic harness to pinpoint faulty RAM chips and the 6526 chip causing issues.

  • What is the outcome of Adrian's repair efforts on the 64C machines?

    Adrian successfully repairs all five machines, replacing faulty components like CIA chips and RAM. Despite potential issues, he recommends the 64C as a reliable machine.

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Summary

00:00

"Fixing Commodore 64C machines in basement"

  • Adrian has five broken Commodore 64C machines in his digital basement.
  • The machines are short board models with later cost-reduced keyboards.
  • Short board 64s were less common outside North America due to the shift to 16-bit machines.
  • Troubleshooting tools include an oscilloscope, diagnostic cartridge, reliable power supply, and video output display.
  • Adrian uses a ZIF64 machine for testing video output and power supply functionality.
  • He encounters a black screen issue on one machine and suspects faulty DRAM chips.
  • Adrian uses a dead test cartridge to diagnose the issue with the DRAM chips.
  • Replacing the DRAM chips resolves the black screen problem on the first machine.
  • The second machine with a bad CIA issue is found to have a dirty keyboard causing typing problems.
  • Cleaning the keyboard resolves the issue, and the machine is fully functional.

14:30

"Faulty Sid chip replaced, restoring functionality"

  • The PCB color is green, unlike the yellow one previously observed.
  • The external color RAM is similar to the last one, but the backside appears untouched.
  • Components were hand-soldered, leaving flux residue, while the rest was wave soldered and cleaned.
  • Most components are soldered in, except for the CPU, Sid chip, vic2, and clock synthesizer.
  • Upon powering up, a flashing cursor indicates potential functionality.
  • A diagnostic ROM and test harness are connected, with contacts cleaned due to dirt.
  • The keyboard is identified as faulty, possibly due to dirt hindering functionality.
  • The Sid chip is deemed faulty, affecting paddle ports and keyboard functionality.
  • The 6526 chip handles keyboard and joystick ports, with potential issues identified.
  • The faulty 6526 chip is replaced with a known working one, restoring keyboard functionality.

28:21

"Troubleshooting 6526 Chip in Vintage Machines"

  • The chip 6526 is crucial for the machine's functionality, and alternatives like 6522 or 6520 are not compatible.
  • The oscilloscope probe on the keyboard connector reveals expected pulses necessary for keyboard operation.
  • Absence of expected pulses indicates a problem with the 6526 chip, confirmed by diagnostic ROM recognition.
  • A diagnostic harness is used to power up the machine, confirming the 6526 as the only faulty part.
  • The faulty parts in the machine are identified as two RAM chips and the 6526 chip.
  • The next machine encountered displays a black screen, likely due to bad RAM, which is quickly replaced.
  • The machine with a non-flashing cursor is suspected to have a faulty CIA 6526 chip, which is confirmed by diagnostic tests.
  • The machine's date codes suggest it was produced in 1986-1987, making it a reliable longboard model.
  • The non-flashing cursor issue is attributed to a faulty CIA chip, possibly damaged by static charge from joystick ports.
  • The PLA's chip select line is checked to ensure proper functioning, ruling out a potential cause of a black screen.

42:35

Repairing Commodore 64C Machines: A Success Story

  • Normal triggering of the other component, not controlling the keyboard
  • Power cycling the computer to address normal activity
  • Flashing issue rules out PLA as the problem
  • PLA outputs held low causing black screen, leading to bus conflict
  • Socketing the 6526 to potentially fix the machine
  • Pin detachment observed on the 6526 chip during removal
  • Damage on the chip, possibly due to melting, not from the back side of the board
  • Installation of a new socket and 6526 chip from another machine
  • Successful repair of the computer, with a strangely burned pin left on the chip
  • Discovery of a warranty seal on a 64C machine made in China, unlike others made in the USA
  • Opening the machine to find a broken power switch, despite the warranty seal
  • Replacement of a capacitor and testing the machine for functionality
  • Identification of bad RAM chips from different manufacturers in multiple machines
  • Repairing all five 64C machines, with some needing new 6526 CIA chips and empty sockets
  • Recommendation of the 64C as a more reliable machine, despite potential RAM issues
  • Speculation on the power switch issue possibly caused by shorted RAM chips
  • Observation of a possibly faulty capacitor from the manufacturing stage in one machine
  • Successful repair of all five machines, concluding a mini repair-a-thon video.
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