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Repairing CFLs 101!

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Vince:
As you may know, CFLs are usually not the highest quality electronic goods around. While a majority of CFLs burn for their entire rated life and burn out without any problem, a good, non-neglectable part of them die prematurely because one single component in the ballast fails. In many cases it's always the very same component, and this thread will show you how to find that failed component!

All you need is some electronics basics, a soldering gun, a desoldering pump, some solder and a multimeter (with capacitance setting if possible).

There are tons of CFL diagrams on the net, and I have the diagram for the GE helical 26W model if someone is interested to have it. The principle is always the same, few components change from a model to another. It is always based on a HF push-pull 2 transistors oscillator.



The diagram shown here is for a 230V CFL, but 120V circuits have few differences.

Here's how I proceed from the harvest at the recycling centre to free, working lamps:

- First, look for CFLs with non-blackened ends, this may be a sign of a bad ballast that can be easily repaired. Feel free take a couple of burnt out CFLs to get you a good supply of spare components.
- Open the CFL with a flat screwdriver. Be careful during this step! The base may be glued, if it doesn't seem to open at all, forget it. But most CFLs from major brands are just clipped and can easily be opened.
- Then take your multimeter to the Ohm setting and first check the fuse. If it's open, the bridge rectifier of filter capacitors may be shorted. In that case check both RF and voltage regulating caps, if one is shorted, replace it.
- Check the lamp electrodes. No need to troubleshoot any further if one electrode is open. Although you may want to check the ballast with a working tube if you have one in hand.
- If both the fuse and electrodes are good, set your multimeter to the capacitance setting and check the capacitor between lamp electrodes. This is the cap that receives the highest voltage peak at startup, and usually the one that fails. Your multimeter should normally find a value anywhere from 1 to 4nF. If it doesn't move, the cap is shorted. Replace it and in most cases the CFL will then work fine!
- If that cap is good, check the cap in series with the lamp (C6), that cap being shorted may only cause the CFL to flicker and won't usually prevent it from starting, although it may be open, which is rare but possible.
- In the case the two previous caps are good, check all the other caps in the circuit. In the diagram above, If C1 or C2 is shorted, it may prevent the oscillator circuit from starting. Otherwise the problem could be related to the HF transformer of the other oscillator control components, these are harder to troubleshoot but are fortunately rare. Such problems may cause the transistors to blow, or not to start at all.

Most prematurely failed CFLs are fortunately easy to repair, and with a little work, like 20 minutes at the most per CFL, you may get a virtually unlimited supply of CFLs! The only downside is the kinda unpredictable lifespan of the repaired lamps. But they're free anyway LOL.

Form109:
Very Nice Vince!

Medved:
The only failing components I've seen:
Result of lamp EOL and/or dry joint: Fuse, transistors with R1, R2, R3, R5, sometimes C3
C4 EOL: fuse, sometimes lamp and consequently the above.
If only the lamp filaments glow white (discharge is present), on ly C3 fail by itself and it's replacement would fix the problem.
If lamp filaments only glow yellow (only incandescent glow, discharge not present), again the C3 is failed, but due to lamp EOL. Sometimes the lamp is damaged as consequence of above, but such damage is rare, as most likely the filament would physically break.

Generally repairing the ballast make sense, when you want to use it with fresh lamps, as most of the faults are the consequence of the lamp loosing the emission electrode coat, so even if the lamp appear good, mostly it will fail very soon again.
Whole circuit is working well as ballast for PL-S, even for 2-pin ones (function of C3 is then taken by the capacitor connected parallel to the starter).
But here I would recommend to reconnect the cathodes of D2 and D3 to the base of the respective transistor, as their top killer is the excessive EB (reverse) voltage during the ignition/cold cathode phase. Such reconnection would clamp this voltage and transistors become way more robust in surviving lamp EOL.

GEsoftwhite100watts:
can you send me the diagram for the GE helical 26w? By the way, are all GE helical wattages similar?

SeanB~1:
The electronics inside a CFL are pretty much all the same, as you can not really put much into the space. There would be a difference between the common lamp for 230V and one for 115V operation, and a different one for a 3 way lamp. The basic system will be the same, just differences in the input side.  There are IC's for lamps, but they are not often seen in CFL bodies, as they cost more than the 2 transistor system, and would need the 2 transistors in most cases anyway.  They will be seen in dimmable lamps, as this needs a more complex circuit.

Your 26W lamp will be basically the same as the illustrated in many respects, just a different inductor, and most likely nothing else.

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