Repairing CFL Lamps


What you do when the CFL lamps in your home stops working? You probably throw it and buy a new one. What if I tell you that most of these dead CFL can be easily repaired at home? By sparing a little time to repair it, you can save a lot of money. To start with, all you need is few tools and tiny knowledge of electronics which I will tell you here as well:

  1. Flat head screwdriver
  2. Soldering Iron and solder wire
  3. Digital multimeter (cheapest one will do fine)

Buying these tools is not a big investment and for the price of one new CFL, you can get all these three tools which will help you repair not only CFL but many electronic items at home.

When you have a dead CFL lamp to work on, first of all wipe off all the dirt and clean it with dry cloth because these are always covered with sticky dust. Now open it using flat head screw driver. You need to pry open it from the thin gap which is between the body of lamp. Take care while opening that you don’t exert pressure on the glass tube otherwise it can break and hurt your hands.  The two halves of the CFL body is joined snugly and can be taken apart easily.

Don’t be surprised if you find lots of dead insects inside the lamp, they somehow manage to get inside and die from the heat. Just tap on lamp body to remove these dead insects. Once you have it open, you will notice that there is a PCB with lots of components on it and the tube is connected to the PCB with four wires, two from each tube and two AC wire also go to the PCB from the top socket. For ease of working you can de-solder the AC wires and solder them back when done repairing.


Here is the list of components that you will need to check one by one to repair the CFL:


First thing you need to check now is the health of tube. If the tube is good then only the CFL can be repaired, otherwise not. We will use digital multimeter to check the tubes. Set the multimeter on diode mode and connect both the leads (black and red leads) of multimeter to both the wires running out from any one of the tube. Look at the image 1 above, connect the multimeter leads to wire 1 and 2 and then 3 and 4. (marked with pink colour) If multimter shows reading (0 or near about value) for both the tubes then they are good and CFL can be repaired. If any one of the tubes do not show reading then this CFL cannot be repaired. However I would suggest that you detach the PCB from this CFL and keep it for salvaging the parts and using it to repairing other CFL’s in future. Also there is a chance that the PCB is fully working and only tubes are dead, in this case you can swap another CFL’s tube whose PCB is dead but tube is fine. In other words, whenever the CFL is dead, throw only that part which cannot be used in repairing other CFL.

In case where the tube was fine but still CFL not working means that one or more components in the PCB are faulty. Most of the time the culprit is a capacitor which is connected in series to the tube (C1 marked in image 1) Or the resistor (image 2 below) which is connected in series with AC line. You will find this resistor near to the AC wires connected to the PCB and capacitor C1 near to the four wires connecting the tube.



If the resistor is bad you can tell it by just looking at it closely, it will have sign of burns. Image 2 above shows a burnt resistor, however in the PCB it looks fine because only one side of it is visible which appears to be fine. To confirm the resistor is dead or not, use multimeter to check the value of the resistor. Set the multimeter in Ohms mode (set it to lowest value in Ohms mode)and touch the leads to both ends of the wire of the resistor. Multimeter will display the value of the resistor and if it does not show any reading or show abnormally high reading (say above 1000 Ohms) then the resistor is dead. Usually this resistor is of very low value of about 0.5 Ohms and is used as a fuse here in the CFL circuit. To change the part, either buy it from the market (Tip: buy more than 1 always because they are dirt cheap and you will not have to run for it again if you need them in future) or take it out from any other dead CFL board.  Do check other few resistors on the PCB as well for burnt sign and replace if you find any. The color band on the resistor depicts its value.


To check the capacitor (marked C1 in image 1) you will need the multimeter. Again set the multimter to diode mode and connect both the multimeter leads to both the terminals of capacitor. If the capacitor is good then it won’t show any reading (because it’s a very high voltage capacitor with small MFD value) but if it’s bad then it will show 0 as the reading which also means the capacitor is short. Note that colour of this capacitor may wary and not always be green. It can be orange, black or in blue colour as well.

IMG_1999There is one more capacitor which is prone to damage. The filter capacitor which is the biggest capacitor on the PCB, usually at the center and value of around 400V. If this capacitor goes bad then it will have a bulge on the top of it or sign of oil leakage at bottom. If you see the bulge or any oil leakage, change this capacitor as well. Some makes of CFL have two of these caps so check both. Also this capacitor will have its value printed on it and it varies with manufacturer to manufacturer and different wattages of CFL they make.  So before you change any of these capacitors, make sure the new one matches the value of old one you are replacing with.

At this point I would say you can try to connect the CFL to power source and see if it lights up. 90% of the time you are done with repairing job here and it should light up!

After you have changed the above mentioned faulty parts but CFL still doesn’t light up, look at other remaining parts as well for any burnt sign. One part which will not show any sign of damage but can be bad are the two main transistors and sometimes diodes too. We will tell you about it in details in part two of this article.

Mohd. Hashim Khan

I work as a freelance web designer and developer and enjoys fiddling with machines and electronics stuff. I am also working as a part time computer teacher at Aligarh Muslim University. I share my knowledge on various topics here so that others can make use of it and take benefit from my experiences.

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2 Responses

  1. Dr. Bibhuti B. Roy says:

    I am trying to find out part 2 of this wonderful article on CFL circuit repair but ????
    Will greatly appreciate if you mention the voltages at different points of the circuit which can be measured before fiddling with the components. Please do reply.
    Dr. B B Roy.

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