Decoupler test tool

[Terry]

Good idea but you are only checking for lost capacity. When capacitors fail its the dielectric that breaks down, so you should check for leakage first, this means disconnecting one end from the circuit it is in. I have also found that a leaky cap will read low capacity, so your test may be trying to tell you that the cap is leaky

My experience of the tubular ceramic decoupling capacitors used in most vintage TVs is that most go open circuit, causing the IF stages to go unstable. However, such instances were isolated and I never recall having to replace more than one in any set I repaired, thus it was not worth the time and money involved in carrying out a blanket replacement programme on any set, particularly if it was hand wired - much more efficient if you could accurately track down the culprit rapidly, which this tool does.

Usually a shorted ceramic would be self evident on sight if there was any blackening of the ceramic coating or, if the HT feed to it was fed through a series resistor (as was normal) the charred resistor would point the way. Voltage checks would pin point a leaky capacitor.

This tool is purely and simply for tracking down a specific known fault after other obvious alternatives have been checked.