Commodore PET 2001 General Maintenance

Commodore PET 2001 with top lifted open.

Proper maintenance of the Commodore PET 2001 is essential to preserve its functionality and prevent age-related failures. This guide covers cleaning, keyboard servicing, capacitor replacement, power supply care, and CRT-specific issues unique to early Commodore PETs.

Regular Cleaning

The PET 2001 features a hinged metal chassis for easy internal access. Dust buildup and oxidized contacts are common in these early systems.

Internal Cleaning

• Disconnect the PET from mains power.
• Carefully lift the PET's top panel to access the motherboard and CRT.
• Use compressed air and an anti-static brush to clean:
  • The motherboard (especially under ROM/RAM sockets)
  • Power supply area
  • CRT yoke and anode cup region
  • Cassette deck area (for 2001N models)
• Use isopropyl alcohol (>90%) and cotton swabs to clean stubborn areas, but avoid soaking.

External Case and CRT

• Wipe the painted metal case with a mild soap solution on a damp microfiber cloth.
• CRT screen can be cleaned using a lint-free cloth and glass cleaner sprayed onto the cloth.
• Avoid aggressive rubbing of the screen label ("Commodore") which may degrade over time.

Power Supply Maintenance

The PET uses an unregulated linear power supply without a switching regulator. While robust, they do require inspection:

Inspection Checklist

• Check transformer and rectifier board for heat stress and corrosion.
• Examine all RIFA X2 safety capacitors — these are known to explode with age. Replace immediately if original.
• Check solder joints around bridge rectifier and voltage regulators (7812, 7805, etc).
• Confirm voltages at the edge connector:
  • +5V, -5V, and +12V should be within 5% tolerance.

Capacitor Replacement (Recapping)

Like many late-70s electronics, the PET contains aging electrolytic capacitors.

Symptoms of Failing Caps

• Vertical hold issues on CRT
• Unstable startup or flickering screen
• Noise in cassette audio playback/record
• Random freezes or garbled text

Recommended Areas to Recap

• Mainboard decoupling capacitors (especially around the 6540/6550 chips)
• CRT analog section (for power filtering)
• Power supply (main filter caps, axial types)

See the Commodore PET 2001 Capacitor Replacement Guide for a full list.

Keyboard Maintenance

The chiclet keyboard on early PETs (especially the 2001-8) is notorious for key bounce, non-responsive keys, and deterioration.

Cleaning Procedure

• Remove keyboard from the chassis.
• Disassemble keycaps and springs (carefully photograph layout).
• Clean contact pads on the PCB using isopropyl alcohol.
• Polish carbon contact domes if applicable.
• Inspect for lifted traces or oxidized vias.

Repair Tips

• Use conductive paint to restore worn-out pads.
• Replace deteriorated foam/copper domes with modern equivalents (keyboard repair kits exist).
• For permanently dead rows/columns, trace the keyboard matrix and check solder joints or connector oxidation.

Common Failure Points

ROM and RAM Sockets

• The original PET 2001 uses ceramic-packaged 6540 ROMs and 6550 SRAMs in notoriously flaky sockets.
• Symptoms include:
  • Blank screen
  • Garbage characters
  • Lock-ups or repeating startup tone

Remove, clean, and reseat chips using DeoxIT. Replace broken sockets with turned-pin variants if needed.

Cassette Mechanism (Optional)

The internal cassette recorder in early PETs may suffer from:

• Broken drive belts
• Oxidized heads
• Dirty read/write contacts

Clean with head cleaner fluid and demagnetize if possible.

Display-Related Issues

• Cold solder joints on CRT neck board or deflection board are common.
• CRT brightness/focus may drift — use internal trimpots for focus and brightness (accessible on deflection board).
• If the CRT fails to light up:
  • Check filament voltage
  • Verify flyback transformer and HV section

Socket and Connector Cleaning

Many ICs are socketed — an advantage for repairs, but also a source of faults.

Steps

• Gently remove suspect chips (e.g., VIA, PIA, ROMs) using a chip puller.
• Clean pins with isopropyl or contact cleaner.
• Inspect for green corrosion or black oxide buildup.
• Reseat firmly or upgrade sockets.

Diagnostics and Burn-In

Diagnostic Tools

• Use a PET tester ROM (e.g., dead test cartridge or test harness) for RAM and ROM diagnostics.
• Use a logic probe or scope to check clock (phi2) and reset behavior.

Burn-In Tips

• Leave PET running on test pattern for several hours to identify marginal components.
• Monitor voltage regulators for excessive heat.

Voltage Test Points

Use a multimeter to check:

• +5V at 6502 Vcc (Pin 8)
• +12V on cassette motor supply
• CRT filament voltage (typically ~6.3VAC)
• Mains side capacitors should not show leakage or bulging.

Tools You’ll Need

• ESD-safe screwdriver set
• Chip puller or spudger
• Isopropyl alcohol (99%)
• Contact cleaner (e.g., DeoxIT)
• Soldering iron with fine tip
• Capacitor tester (optional)
• Logic probe or oscilloscope (advanced)

Related Pages

• Commodore PET 2001 Troubleshooting Guide
• Commodore PET 2001 Capacitor Replacement Guide
• CRT Discharge Procedure