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Repairing CFLs 101!

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Medved:
There are little variants in the output stage too, mainly when dealing with medium wattage tubes on the 120V mains as an attempt to go around the problematic doubler on the input (the weak output compromise the filament fusing functionality as an EOL protection).

The 3-way lamps are technically dimmable ballasts, so you need a bit more complex controller then the simple 2-transistor power oscillator.

Vince:

--- Quote from: GEsoftwhite100watts on October 07, 2011, 10:36:20 PM ---can you send me the diagram for the GE helical 26w? By the way, are all GE helical wattages similar?

--- End quote ---

You can download the PDF document right here!

Just make sure you are familiar with electronics and diagrams before getting started!  ;D

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Now more details about tests of the most commonly failed components:

Capacitors

Capacitors are probably the #1 most common cause of ballast failure. Two capacitor types are widely used in CFLs, the electrolytic and the polyester film.

Electrolytic caps are known for their large values, mostly in the uF range. In CFLs they are used to filter the rectified alternative current to get a DC current with a higher mean voltage, which will be more efficient. In other words instead of "bumps", the current form will look somewhat like blunt sawtooth. Those filtering caps are exposed to a peak voltage varying from 170V to over 300V. Despite being kind of low, the cap is exposed to more or less intense heat, conditions in which they don't age too well.

Most capacitors of this kind will fail shorted. It is easy to check that with an ohmmeter. A capacitance meter is even better, since a shorted cap gives 0uF.

Electrolytic film capacitors can be made with very high breakdown voltages and are usually in the nF range. Don't be surprised to see 1.5kV rated caps in a CFL ballast! But even if they are rated that high, capacitors and high voltages don't make the best combination. The capacitor connected in series with the tube filaments (C3 in the diagram above) is exposed to hundreds of volts each time you turn on the CFL. If that capacitor ever shorts, the tube will never start.

Here again you can check that type of high voltage caps (removed from the board please! D: ) with a capacitance meter, or an ohmmeter if you have nothing else. A reading of 0nF of 0 Ohm indicates a shorted capacitor.

Medved:
The capa-meter reading of the shorted out cap strongly depend, how the meter exactly work. Normally it should read "overflow" (as infinite capacitance yield zero impedance), but many instruments go out of correct operating point, if the terminals are DC shorted and then read the zero.

For electrolytic is very useful the ESR meter. It is not as common tool, but the only one able to show you the soon-to-fail electrolytic capacitor (the failed seal, so water deficiency in the electrolyte, demonstrate itself by rising ESR, while the capacitance is still unchanged).


@Vince: In the 4th section you have a typo: The word "electrolytic" should not be there...

SeanB~1:
ESR meter is more important than capacitance meter on high value electrolytics, as many will show high ESR well before any signifigant capacitance loss. On high voltage low value electrolytics you need to measure both, as the impedance is becoming an important part of the measurement.

On motor capacitors and PFC capacitors I measure both capacitance and insulation resistance, as these capacitors tend to suffer from breaking down under running conditions.

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