Focus drift problem in IIIA monitor caused by failing voltage tripler

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2006Monitors forum

20 years old. Gear and prices may have changed since.

A IIIA monitor that starts with sharp focus but gradually becomes blurred over one to two minutes, usually progressing from right to left, and resets when powered down is typically caused by a failing voltage tripler in the base housing
The vertical hold adjustment is located inside the base of the monitor and can be accessed with a small red or orange knob connected to the board at the tube base
A temporary fix involves adjusting the red or orange control knob at the base, though the focus will eventually drift again
The voltage tripler is a plastic housing filled with silicone that contains a high voltage cascade, and when failing may show visible sparks or arcs under the silicone in a darkened environment
High voltage capacitors inside the tripler frequently fail and can sometimes be replaced by removing components from the silicone housing
A solid state cascade from a color television can be substituted for the failing tripler, typically costing around four dollars
A replacement solid state cascade unit can be mounted directly inside the monitor housing with rewiring to reduce reliance on umbilical cords, requiring only a resistor to limit current through the rectifier tube
When a IIIA monitor fails completely, the entire base and electronics housing below the gimbal are typically discarded since the monitor is integrated into the overall setup

The repair difficulty and feasibility of replacing the voltage tripler varies, and expert assessment is recommended before attempting repairs
Temporary adjustments may only maintain focus for short periods before drift recurs
A solid state cascade replacement is feasible but requires knowledge of high voltage electronics and access to appropriate measurement tools
The manual describing this repair may no longer be available in accessible forums