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Never Seen Before- LED Bulb Post Mortem And Repair

By on February 15, 2016









Wow, one of my LED bulbs broke down! According to my earlier calculations I should not have seen any of those dying until I reach the respectable age of 99 years old! Let’s go back to the math…


I bought them in mid-2012 when I moved from an apartment to a town house.  I can remember perfectly when I replaced the permanently fixed fluorescent tube mounted above my desk with 4 desk-type lamps fitted with LED bulbs, two above the desk and two above the workbench. The LED bulbs were guaranteed 25000 hours, as printed on the box! The lighting in my office is quite good, so I only use those auxiliary lamps when I need a bit of extra light, for some delicate work or to take photos… If I say a maximum of 2 hours a day it is probably overstated but let’s take this as a base for calculations:

25000 hours divided by 2 hours/day = 12500 days

12500 days divided by 365 days/year = 34 years (ignoring the decimals)

So from 2012 the bulbs are supposed to last until 2012 + 34 = 2046! Yes, I would be 99 years old! Total disbelief, I tried the bulb in other sockets in other lamps, nothing. It was really gone.

Well, the good thing of this early demise is that I had the opportunity to open the LED bulb and see what is inside. The first problem was to find out where to start. It is all plastic and there is a groove around the bulb somewhere in the middle. Maybe using a cutter we shall be able to cut it open? Not really, the pictures below summarize the battle:

led bulb repairing

led light bulb reair

Finally we had something to work with, a nice little PCB and a LED board. Let’s start with the LED board. It is fitted with 22 LEDs and has a provision for 4 more:

led bulb components

Each LED tested OK individually with the analog ohmmeter, giving a bright light on the X1 range. The Peak Atlas gives a forward voltage of 2.6 V. At this stage it was not possible to test the whole board because the LEDs seem to be connected in series. We would need a voltage of at least 22 x 2.6 V = 57.2V. None of my instruments can do that…

atlas dca 55 tester

Now let’s have closer a look at the board:

led bulb circuit board

led light bulb repairing

Nice and tidy, no sign of overheating. However we can spot a number of cold joints. Would this be the problem?

I started by measuring a few obvious components, capacitors, diodes, transistor etc… no one was found defective. Then I re-soldered the cold joints. Now it was time to reconnect the LED Board and do some measuring. And guess what? It was working!

series light bulb test

The voltage across the LED board indicated 66.6 V and the current 140 mA. This confirmed that the LEDs are connected in series. Checking at the datasheet of the EMC 3030 LED confirmed that the current of 140 mA was within specs.

Everything indicates that the controller is a mini-SMPS acting as a constant current source, contrarily to our SMPS which usually act as constant voltage sources. To prove this I needed to use a load corresponding to the LED board. Then I should vary this load and see if the current remains constant. With 66.6 V and 140 mA the LED board corresponds to a resistance of 475 Ohms (and approx. 10 W). I don’t have this value but 10 x 47 Ohms resistors in series will do the trick. To vary the load I would either short one of the resistors or add one more resistor.

bm867s meter

With 470 Ohms the values are 64.68 V and 139 mA.

With 470 – 47 Ohms (423 Ohms) the values are 60 V and 140 mA

With 470 + 47 Ohms (517 Ohms) the values are 69.7 V and 138 mA

We can see that the controller nicely adjusts the voltage to maintain a current of around 140 mA. Like this the manufacturer can add or remove a few LEDs to make different wattage bulbs without changing anything on the controller board.

The last thing I was keen to check was the input power. At the output we have 66.6 V with 140 mA which corresponds to 9.3 W. Measuring at the input I found 244 V and 55 mA which corresponds to the marking on the bulb (220-240 Vac 57 mA). So the power would be 244 x 0.055 = 13.42 W? Is this correct? The marking on the lamp is 10 W so are we getting ripped off? Is this lamp using 13.42 W, 30% more than advertising?

The answer is not so simple. In DC or AC with a purely resistive load, the power is given by Voltage x Current. In AC, if the load is not purely resistive, there will be a shift between Voltage and Current. This means that when the voltage is maximum, the current is not etc… so we cannot simply multiply voltage with current because they don’t have their maximum value at the same time. We have to consider the difference of phase. This phase difference is called the Power Factor (PF). It is in fact the Cosine of the phase difference in degrees! When there is no phase difference, PF =1 (Cosine of 0 degrees = 1). A  PF of 0.9 is considered as normal. Less that is usually not good.

And the real power is expressed as:

P = V x I x PF

A quick survey on the Internet taught me that the power factor of LED bulbs if far from ideal and can vary between 0.5 and 0.9. As I do not have the equipment to measure the power factor I will assume that the input power is 10 W, as advertised. In such case:

P = V x I x PF

PF = P/VI = 10 W / 13.2 VA = 0.75  ?

I couldn’t resist finding a way of looking at the current’s shape. For this I needed a current transformer so I could connect the oscilloscope safely. I found one in my junk box, recovered from an old UPS. For the voltage I used a 240V/6V transformer. Like this my oscilloscope is safe. Never try to connect your oscilloscope to any part of the 110V/220V/240V mains!  It would be instant destruction!

Using a standard light bulb (filament type) first I could see the shapes of voltage and current:

 voltage and current

The phase shift is due to the use of transformers. Indeed for a light bulb both should be exactly in Phase as the light bulb is a pure resistive load.

Then replacing the light bulb with our LED bulb:

voltage and current scope

The sine wave is still our voltage. The hairy funny wave is the current (Note that it is shifted by about 2.5 ms because of the transformers). No wonder why, by multiplying the voltage by the current we do not get the expected result! Maybe the power factor could be the subject of another article. 


For being one of the earlier LED bulbs that we could find on the market this one is not too bad. The construction is solid and there is no sign of overheating after a few years of use. With a better soldering quality, without cold joints, this bulb might have had a chance to live until 2046! Who knows? While de-soldering a few components to measure them I found that the solder used was difficult to melt and needed a much higher temperature. Probably Lead Free Solder…

We could repair those bulbs. Not for the money worth but for fun, to sharpen our skills and improve our knowledge.  Providing we find a less destructive way to tear them down!

gerald musy







Gerald Musy

Penang, Malaysia


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  1. Jayant Gholba

    February 15, 2016 at 10:12 pm

    Excellent article. I appreciate the attitude of investigating thoroughly.

    • Gerald

      February 16, 2016 at 1:44 pm

      Thanks Jayant for your support

  2. Parasuraman S

    February 15, 2016 at 11:08 pm

    Great! Something new to learn, though many of your calculations and formulas are German for me! A big thank you for sharing this wonderful info!

    • Gerald

      February 16, 2016 at 1:47 pm

      Thanks for your support Parasuraman. Don't worry about the calculations. Important are the results and conclusions. I know you are an excellent practical man with a wealth of experience.

  3. Dennis Breda

    February 15, 2016 at 11:23 pm

    Thank you Gerald. Your article is a great hands on review of "book learning formulas" regarding power factor. Beyond that I appreciate the comerodery of sharing our trade from all over the world.

    • Gerald

      February 16, 2016 at 1:48 pm

      Thanks for your support Dennis

  4. Albert van Bemmelen

    February 15, 2016 at 11:49 pm

    Thanks Gerald. You shed a bright light on this new field of darkness. Because of the higher bulb temperature they probably indeed used higher melting solder. But since they didn't do a good job of it, because of the cold solder joints, normal solder maybe can be used to fix this. (also preventing the smd components from getting all cooked when using higher melting solder). I guess that the LED bulb still won't get so hot that the components drift from their solderpads? PS: they often say that it is very dangerous to connect a scope input directly onto the mains. Even if my scope can measure upto 400V (dc + peak ac), 800V p-p ac at 10KHz. And if use an 1:10 probe it only would mean a voltage of only 40V ac. But they probably mean to say that only just touching the Phase of the Line Voltage is dangerous for the user without using a safety transformer inbetween. It probably won't kill my scope's input circuit.

    • Gerald

      February 16, 2016 at 2:01 pm

      Thanks for your comments and support Albert. The solder is probably lead-free because, even it was made in China, the manufacturer is a European company. Indeed this lamp doesn't run very hot and there was no sign of those standard components (even the electrolytic cap)suffering form overheat as it is the case when you open a CFL lamp.

      Regarding the scope, even with an isolation transformer it is not safe. You find good info at the following site:

      There are special probes for this purpose but they might be a bit expensive. I used a current transformer for the current and a step down transfo for the voltage. We find cheap current transformer on Ebay, for about US$ 5.00:

      I ordered one of those for doing some testings. This is the way to go.


  5. Robert Calk

    February 16, 2016 at 2:24 am

    Nice article Gerald. Thanks. The majority of problems I find are caused by bad solder joints.

    • Gerald

      February 16, 2016 at 2:04 pm

      Thanks Robert,

      All indicates that lead-free soldering is going to keep us on the job 🙂


  6. Joseph

    February 16, 2016 at 4:24 am

    I love you. Your work is so thorough. I want to be like you. How can I do it? I wish I have an oscilloscope to experiment with here in Nigeria. Ordering an old tectronix from the US is impossible here. Thanks for the article. I'm motivated.

    • Gerald

      February 16, 2016 at 2:05 pm

      Thanks Joseph

  7. Anthony

    February 16, 2016 at 5:14 am

    A very interesting and educational article Gerald ! Thanks for taking the time to share it with us.
    Best Regards

    • Gerald

      February 16, 2016 at 2:07 pm

      Thanks Anthony

  8. Mark

    February 16, 2016 at 5:59 am

    Hey Gerald,
    Thanks for your insight into the LED light.
    I still have one of your previous articles on 'The Light Bulb' printed out on my lab desk that I want to experiment with. Unfortunately, time is always a factor. You learn so much when you just experiment to find out how things operate under given conditions. This is something that you don't always learn when just carrying out repairs.
    Keep up the good work!

    • Gerald

      February 16, 2016 at 2:11 pm

      Thanks Mark. Yes, experiments is the best way to learn. It is time consuming though and one has to set priorities.


  9. Yogesh Panchal

    February 16, 2016 at 3:40 pm

    Thanks for informative article! Please do keep sharing.

    • Gerald

      February 17, 2016 at 8:07 am

      Thanks for your support Yogesh

  10. Suranga Electronics

    February 16, 2016 at 4:26 pm

    An excellent explanation. Thanks Mr Gerald Musy for sharing your knowledge.

    • Gerald

      February 17, 2016 at 8:08 am

      Thanks for your support Suranga

  11. Paris Azis

    February 16, 2016 at 7:22 pm

    Hi Gerald

    Thank you for this excellent presentation. Your article reminds me of another excellent one I happened to read long ago in the web under the title “The CFL lamp should be banned and not the incandescent one”.
    The truth is that if someone tries to scale the pros and cons of each type of lamp the scale will fully favor with pros the good old incandescent lamp. This was the final extract of this article, written by an engineer who was making clear that he knew his “lighting” professional subject very thoroughly.
    I don’t remember every detail of it but his main points were that all of these “economical” types of lighting suffer from a plethora of drawbacks, first being the really bad power factor. The avalanche was going on with their escorted limited life, far below the advertized one, due to the overheating of their internally and fully closed PSU and of course the fact that this overheating is furthermore accelerated simply because the lamps generally are installed in the reverse way than the considered as normal, that is, their PSU should be down and the lighting element up, on top of it, and not vice-versa as the usual case is. In other wards all lamps should be mounted on a stand holding them in an upward position, with their can and PSU at the bottom and not at the top. But this unfortunately represents only a small fraction of their position in bulb-holding and lighting systems, with the usual one being the reverse of the previous, that is, they look downwards. Then the heat has no way to radiate to the environment and as a system it degrades over time until we have all those common premature failures rendering their use not as economical as their advertisements!!...
    Apart from that and as regards the protection of the environment, when an incandescent lamp dies, we through away a piece of metal (the bottom can), a negligible amount of tungsten-wolfram metal (its filament) and an equally negligible volume of glass.
    But when we through away a defective CFL, despite the fact that in most cases only the lamp’s filament is open, we throw away a perfectly working electronic assembly or in terms of raw materials: copper, ferrite etc reflecting a lot of money which goes directly into the garbage bin. And now the same story already holds true for the LED lamp technology, due to the same reasons exactly. And I find this an amazing nonsense, agreeing fully with the conclusions of that article I saw long ago…


    • Gerald

      February 17, 2016 at 8:39 am

      Thanks Paris for your support and comments. Definitely the power factor is a real disadvantage of those lamps and things are not getting better. The new LED bulb I just bought to replace the faulty one is rated 9 W and 80 mA! 240 V and 80 mA (if it is true, I haven't measured it yet) would correspond to 19.2 VA. For 9 W of real power! The lamp comes from the same manufacturer and let me think that the first one, bought 4 years ago (10 W and 55 mA), was much better. Some cost cutting exercises may have happen in between! I read somewhere that electricity companies are considering charging for reactive power on domestic users. That will become really interesting.
      Cheers, Gerald

      • Paris Azis

        February 17, 2016 at 9:54 pm

        Dear Gerald

        Articles like this one of yours, apart from being very interesting for me, unfortunately cause me an undesirable side effect (and I would like to believe that the same holds true for many other readers interested in seeking an answer in questions or dilemmas like; what is true or false, what is worthwhile or worthless, what represents a real value and what “shines like gold” but it is simply “polished bronze” in our lives…And I am referring to modern marketing and its connection with modern industry…
        In simple words I am totally disappointed of what is going on (at least but not exclusively) in the world of electronic products.
        Anyway I belong to “the old school” and therefore I believe that the industry in general should cover existing human needs and not create needs in places they are simply not needed.
        All I am trying to say is that yes I need a washing machine for my laundry but I don’t really see any reason for this machine to include a TV set on it. Similarly, I don’t see any reason to replace my good old CRT TV set with a plasma set (only because it is old technology. I am a user. I don’t buy technology because I don’t need it. But I need to watch TV for the news and enjoyment. If I don’t have one I will chose one from the currently existing technology. But as long as this set I already own works perfectly I don’t see any good reason to throw it away because its technology is old. It still covers my needs)….
        And how the modern society reacts on these dilemmas makes me really sick. I really can’t stand this any more and feeling that I cannot do anything about it makes things worse to me. Moreover if I connect the fact that people tend to throw away their goods after the first failure without any attempt for repairing them, this really drives me crazy. The bottom line Gerald is that I see “Logic” diminishing rapidly over time and this is the basis of my disappointment.
        But I don’t blame you for this excellent (despite the “wound scratching”) article!!...
        Take care of yourself and bring more similar articles under the light of publicity. They are really worthwhile as per the context of all these above (at least)…


  12. Henrique J. G. Ulbrich

    February 16, 2016 at 10:38 pm

    You are right, Paris. Some kinds of "progress" act in a reverse way. Concerning CFLs, the main problem is the bad quality of almost all the products in the market, i.e., low duration. This means: a higher quantity of products thrown away. Not only copper and ferrite, as you've mentioned, but mainly mercury, that's hazardous to the environment.

    • Paris Azis

      February 17, 2016 at 8:58 pm

      I agree Henrique. I just forgot these droplets of mercury hidden therein which is the worst case scenario if a CFL lamp gets broken when being installed in a closed room. (And I wonder in this case if this reference has to do with only its mishandling during either its installation or de-installation, or if it referenced to its possible breakage when it is working, when these mercury droplets will be evaporated within the lamp and then the mercury cloud will be spread all over the place after the breakage). Next to that, as I read in the web, a special contractor is needed having the proper tools in order to clean the area and bring it again in a health-safe status for the people living therein …And the cost of such a case reaches very easily the amount of 3.000$...Simply amazing isn’t it? Finally, if this holds true and we call it progress please let me prefer using candles! They won’t hurt that power factor whatsoever!


      • Gerald

        February 18, 2016 at 5:42 pm

        Thanks Paris and Enrique. Totally agreed with you guys. I am also from the old school myself (not yet 99 though 🙂 and I love old technologies. Missing the time when engineers were rewarded for quality, and durability rather than for saving a few cents in using lower quality components.
        Not much we can do but keeping saving equipment from the trash whenever we can.


        • Paris Azis

          February 18, 2016 at 8:16 pm

          “Old” was never meant and never will be a synonym of “useless”, but, again, this needs application of elementary logic to admit it…which is exactly what tends to be the weak link in our modern life…
          Anyway…as you said, the only thing we can do is to save as many of equipment as possible from the garbage bin…And this is what we do!

          Thanks again Gerald

  13. Philip

    February 18, 2016 at 5:15 pm

    This is brilliant.

  14. Albert Hoekman, Holland

    February 20, 2016 at 12:51 am

    Nice job Gerald. Thanks for sharing the article, keep on going.

  15. Ulises Aguilar Pazzani

    October 3, 2016 at 11:35 am

    good after noon MR Musy ,great article not finish yet like readding your article learn a lot thks again

  16. Hadi Rizvi

    June 21, 2018 at 12:51 pm

    Thanks for sharing your information about led bulbs, really the information and calculation are very useful to students.


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