24/04/2026
Microbee Monitors (AKA Thomson VM3101 and Commodore 1201). A labour of love on display here / no stone left unturned. Outline of Work Completed for both monitors unless indicated otherwise
Component Replacement and Upgrades
• Capacitors: All electrolytics were replaced, visual inspection shows physical leakage (e.g corroded legs) along with sticky surface to PCBs. Date codes show 186 (2025-1986=39 years). The Commodore spec has sound and required a few more caps for that circuit. Majority of replacement capacitors are of identical value in uF, I do remember ‘upgrading’ the 1000uf 10v to 16v.
• Special note: Panasonic ECW-F ultra high ripple current bipolar capacitor fitted in place of existing HF BP cap; mains filter cap 2200uf x2 in parallel with rubber melt fixation; resistor “RA105’ 100ohm 1watt replaced with x2 220ohm 1watt resistors in parallel for twice the heat dissipation nd replaced was indicated as both originals were physically crumbling to touch
Cleaning, Lubrication, and Maintenance
• Potentiometer Cleaning: Light application of Deoxit F5 to clean and lubricate all potentiometers, including front 3 and all adjustment pots
• Soldering Supplies: Used Loctite 60/40 rosin-core solder and Caig rosin flux with a temperature-calibrated Sequre soldering iron.
Fuse and Connection Repairs
• Fuse terminals: All fuses were removed. Dremel micro with brass brush was applied to all terminals to clean off oxidisation and salt speckles then gone over with alcohol and cotton bud.
• CRT Neck pins: Usually crusty as shown in photos, cleaned in multiple passes and lubricated with Deoxit gold protectant
Component Checks and Testing
• Spot Checks: Flyback transformers in good condition, passing ring test
• Passive components: Factory resistors meter in spec and no shorts to ground found
• CRTs: As new visual performance in both e.g sharp text edge to edge at maximum picture level, burn-in absent.
• Excellent outcome in potentiometers: The deep clean and lubricants were tolerated well.
Additional Modifications and Documentation
• Capacitor Specifications: Nichicon PS , Kemet and Panasonic power supply grade caps
• Documentation: Photos were taken and replacement caps tallied. Digikey prices have really gone up. White sticker to both rear shells summarising repair works.
Structural Work
• Reflowed Joints: Most factory solder joints reflowed or de-soldered and resoldered fresh.
• Anode Cap Maintenance: Both cleaned right back with degreaser then fresh Deox R14 well applied to the cap A and B sides and high voltage lead to flyback. Surround CRT bell wiped dry to reduce flashover.
• Internal C8 socket: Rubber fixation and heat shrink to terminals, line cord strain relief incision made to ‘slot’ in replacement C8 cable as supplied by Jeff.
Final Testing and Observations
• Soak Testing: Both monitors were ran for at least 6 consecutive hours using a PAL test pattern generator. I did not test the sound on the Commodore.
