Repair Dead COB LED Light Bulbs
Intro: Repair Dead COB LED Light Bulbs
I have bought a bunch of Chinese light bulbs from eBay which are COB (chip-on-board) units which means a board with a bunch of LED chips soldered on it. They usually run or a month or two and end up dying there about for unknown reasons. Here is my repair technique and maybe why they die and how to repair if you are brave enough to do it. The repair costs about $0.02 each investment if you have the equipment to resolve the problems.
I have repaired nearly 50 of these little things.
These bulbs cost from $1 to $4 on eBay and other places.
Although this process is not that complicated, it does requires a little knowledge of electronics as well as some soldering experience and some safety to follow as well because this is a 110V AC device.
I hope this gives bravery and an idea of how to resolve dying light bulbs to everyone.
STEP 1: Introduction and Background
These bulbs are basically a bunch of little LED chips placed in series on a board and driven by a rectified AC circuit. As with an series circuit, if a component breaks in the "chain", the unit will not work anymore (think Christmas lights here). As in any series circuit, the LEDs draw a current for each unit in the circuit and drop a voltage across each one as it emits light, and hopefully not heat.
In the bulb is a rectifier, a load resister and some filtering capacitors that give the LEDs a DC voltage to live on.
We will check these components out (power supply), and then look at the actual LEDs (parts that are usually broken on this kind of light bulb).
The second picture is a list of the parts and tools you need to accomplish this project.
The list includes:
- Soldering iron and solder
- Multi-meter that has the "Diode check modality"
- tweezers to handle the tiny LED chips
- Pick to move stuff around and serve as tiny fingers
- Replacement LED chips (sell on eBay for like $4 for 1000 chips (like in this picture)
This is a good place to state "do not do this with the bulb screwed into the light socket, because you can get shocked! Do not plug in the bulb until it is put back together and you are sure nothing is shorting out...
STEP 2: Disassemble and Checkout the Power Supply
Open the bulb by snapping off the clear cover and pushing out the electronics boards using a small pick so the boards "pop out".
Once it is all out, look it over to see if you see any physical damage (not likely because it is enclosed).
When you look at the board you will see a rectifier chip and a couple of bigger capacitors (one looks like a "can", and one looks like a roundish piece of candy). The round "can" one is polarized, and as you can see is on the DC side of the rectifier. The candy-looking one is bipolar and is on the AC side. The candy one is to keep "power spikes" out of the light bulb. The "can" one is to make the DC voltage flat and so is a filter to that purpose.
LEDs are diodes that make light, and only use power in one direction (DC). The other direction does not make light and can damage them. The LEDs are linked end to end (think of a chain with each link being one of these LED chips).
Check the candy-looking capacitor with the ohm-meter to make sure it is not shorted out (not likely at all, but just check to be sure). Do the same with the "can" one. Check the rectifier which is four diodes connected in a circlt which makes the voltage go in one direction (DC) from the AC (back and forth) with the diode checker (see picture of setting on meter above): You will see it passing power in only one direction when you measure between the four legs of this chip (Again not normally the problem, but check it anyway).
Once you have these checked out, you are ready to jump into LED land... its all on the DC side of the power supply.
STEP 3: Finding the BAD LED
When you look at the LEDs on the board, the number relates to the power they consume as a whole, and you see this is terms of the number of WATTS they consume (5watt, 7 watt, 9 watt, etc).
Look at each LED to see if you see a burnt one. These burn out mostly because of a defect in their manufacturing process I assume since they always burn out in the middle of the chains of LEDs. You can tell easily a bad LED usually be looking at it and observing a black spot in the middle of the chip (see picture with burnt spot circled in red). This chip needs to be replaced. Check this LED with the Diode checking function of the multi-meter.
Since the LEDs are diodes, you use the DIODE modality on the meter which will exert a little electricity to drive diodes for testing. In the case of LEDs though, it will light them up as the diode is powered slightly, and you can easily tell a bad LED from a good one. When you test the LED in the backward direction, it will remain dark. When tested in the forward direction, it will light (see pictures).
Test in both directions with the meter, taking note as to which direction drives the LEDs. These LEDs are in series, so the LEDs on each panel (board) are all lined up in the same direction (+ & - are all on the same sides of the board in other words). This is important to note when you go to install the new LED in the bad one's place.
STEP 4: Remove Old Bad Chip
Use your soldering iron to remove the old chip by heating both ends and using the pick to remove the bad chip. Do not worry about damaging the chip since it is trash, but be careful not to burn or damage the connection pads that it was connected to on the board... You need them to connect the new LED to.
This is a picture of a bulb with the bad LED removed for an example.
I suggest putting a small ball of solder on the pad before installing the new LED so it has something to grab when you solder it in.
STEP 5: Looking Over the New LED to Replace the Bad One
Looking at the roll of LED chips, open it to take one out, and lay one on the table so you can test it.
Remembering how to use the Diode modality on the multi-meter, you can test the new LED by touching both sides of it with the leads: Remember one direction will cause it to light and the other will not.
STEP 6: Install the New LED in Place of the Bad One.
Take you tweezers and place the new LED where the bad one was paying attention to the polarity that drives it.
The new LED needs to go in the same direction as the other ones so your meter will make each one light up when the leads are placed along side them one at a time.
When you are sure they are all the right direction, tack the sides of the new LED down by using the soldering iron and lightly connecting the solder balls you places earlier and the ends of the new chip will tack into the solder. Practice makes perfect...
test your work by using the meter to light the chips again and make sure you have them all in the same direction (see second picture here).
STEP 7: Back Together!!!
Carefully put the bulb back together and into the clear capsule like it was, being careful that nothing is shorting out or crimped anywhere.
Keep everything and organized when you stuff everything back in the base too.
Now that you have tested all the LEDs and all, screw the bulb in and see if it lights up.
When you see the light, it means you succeeded. Congratulations!
I think the bulbs break because of poor LEDs put in them as I am sure the cheapest and lowest quality chips were used to put them together in China.
Hope this helps you keep from having to replace your LED light investment for the COB bulbs if you have these..
I have to say that I am very intrigued that we can repair a light bulb.. that is something that I would not have thought of just a year ago when we had CFL or incandescent bulbs.
STEP 8: Just in Case You Can Not Find the LED Chips and Still Want to Fix (Addendum)
I was messing aroung with one of my bulbs that I was repairing, and I was thinking about what another person suggested to me about needing one fixed, but not having an LED chip available with him... This started making me think about his situation..
If you do not have one of the LED chips to replace with, you can simply short across the place where the LED chip was at so that you are completing the circuit loop. There will just be one less LED chip in the chain which should not make a very big difference as long as it is just a couple of the chips at most. The result will be less lumens (amount of light produced in total) because there is some LEDs missing (makes sense, yeah?) This will make a burden on the other LEDs in that they take up the slack of the missing one(s). This can be a work around, but suggest you have the missing LED replaced.
151 Comments
ggarri 3 years ago
Thanks in advance, G.
mrstan 3 years ago
mirdamail 6 years ago
Hello. Can you write me the part number of rectifier in bulb? The one in my bulb gave it up and I would like to buy a replacement part, not new bulb.
mrstan 5 years ago
I am looking at your board picture.. I am curious if you can post the other side of the board to see what is populated on that side. This chip looks to me like an LED driver chip instead of a rectifier.. I think the rectifier might be on the other side. The actual rectifier is quite generic and does not really need any specific value. I found several on ebay which would fit into my bulb base.. They must be able to handle 120VAC here, and I think it said 3 or 4 Amps. If you are in another country the voltage and current might be different.. Let me know and I will try to find some kind of part number for you..
mrstan 6 years ago
I think the link I attached is a color LED controller in stead of an LED driver.. Do a search for "LED driver" and I think you will find it. I had some bulbs which had these drivers for the LEDs to save physical space in the bulb.
Digikey has a few here:
https://www.digikey.com/products/en/integrated-cir...
here is another place that I have not heard of before.. must be a chinese place:
https://www.adafruit.com/product/1378
Those are what your are looking for though..
mrstan 6 years ago
hi there,
I do not think that chip is a rectifier. I think it is an actual LED driver chip.
I see one on ebay that might be this one.. Look here on ebay and see if this one lines up with how yours is wired on your board...
http://www.ebay.com/itm/2-1000pcs-WS2811-IC-led-Ch...
I am not sure if you are where the AC is 120 or 220 either. The driver chips are a bunch of filters and waveform shapers to help the LEDs live longer and operate better with less distorted power going to them.. That ebay item has a pretty good diagram of the pins and circuit setup to look over too.
Hope this helps a little..
Larryaka 5 years ago
Hello ,first thanks for the free instruction,just what I needed.
I have a large cob bulb that cost around 60-70 pounds,so I don't want to bin it,and I can see one chip that's failed,but I wouldn't know how to i.d the thing to order a new one.
Could I just bridge the gap with a suitably rated insulated fuse wire to complete the circuit?,to get the rest of them working,or does it need the chip?
Thanks
mrstan 5 years ago
It depends on how many of the SMD chips are in series in your situation... These are lined up in series (end to end) in strands on the bulbs. The more there are, the smaller the effect of one missing becomes. I would say that taking one out and jumping the gap should not cause much of an issue if there are like 8 or so in the line. If there are three though, it might over-drive the remaining two. When you take one out of the circuit, the remaining LEDs have to absorb the voltage drop incurred by the missing one. I hope that makes sense... The bulb I did in the instruction had 8 or 9 in each strand, so the load applied to each of the remaining LEDs was spread out. Do you know what kind of lamp you are looking at? Need to know how many LEDs are in each strand in other words...
I bought the SMD LED chips on ebay for something like $8 for 150 chips as an example... I also noticed that when I replaced the original LEDs with the ones from ebay, they stopped "popping". This makes me think the quality of production on the chinese bulbs was not very good...
offtherails2010 7 years ago
nice 'ible !
ive repaired alot of these too, an on-going practice for less than 100th less than the price of a brand new one !
for me, its *always* heat that kills my SMD LED's.. if not the LED then the resistor or IC, its always something but its always the heat killing the parts.
As an experiment, ive got a 80x80mm fan blowing onto one of these, its not blown over a year but another keeps blowing a different part every 2-3 months lol
mrstan 5 years ago
good call.. leds are sensitive to heat as it alters the breakdown voltage on them...
FranzB10 6 years ago
a few days ago I came across this site in search of a way to repair
one of my LED bulbs. I guess it's chinese as well, gave up 6 month after
purchase....
I used the method you described and found 3 burnt
LEDs. Problem is there is no hint to identify the correct replacement
LED. I tried to find some on the web but w/o success.
here's the
configuration of my LED bulb: 3000k, 110/220V, 7W, 110V DC after the
AC/DC converter, 12 x 2 parallel LEDs in series. as there are 3 bad LEDs
in 24 I could put any replacement LED in even one that isn't that
bright but I have no idea it this would work. a simple calculation to
divide 110V DC / 12 = 9.1V of DC voltage over each parallel pair of
LEDs. I wonder.... the nominal voltage should be 3V for white LED,
correct? so what replacement LED would I need?
mrstan 5 years ago
you can buy replacement smd leds off eBay in rolls of 100 or even 1000. Need to pay attention to the color though, or you will end up with some yellow and some white leds... I see ones in colors now too.. the physical size of the rectangles and color seem to be the biggest factors.
joen 6 years ago
I helped to replace 5 of similar LED lights and instead of throwing them away I took them home and took one apart to see if I could fix them. Then I saw this article. I couldn't figure out how to find new LEDs either. So i decided to use one of the lights as the source of LEDs to fix the others. I just popped off the bad one and popped of a good one from the one source light and soldered it in place. I now have 4 good lights and one pile of parts to fix more. Hope this helps.
oneglimmer. 5 years ago
Ive replaced cob's in bulbs and button etc a few times myself but i was wondering about COB rings? I cant even see any resistors on these types. Sections go out randomly. Can they be fixed or is there a way to reduce it happening. Typically they are 12v 300-600mA for cars etc
mrstan 5 years ago
I am not very familiar with the configuration of these lights, but I expect since they are 12v already like in a car application, there might be a set of three or four in series to drop the 3 or 4 volts which is typical in most string light configuration. Note the in most strings, you can snip them to length as long as you include the set of three smd leds. As to actual real cob lamps, I honestly can not speculate... I would surmise it would somehow need to follow the smd rationale though.. do you have any stats or data on those strips to review?
HHarry14 6 years ago
Thank you for this nice instructable, mrstan. I only found your article after having repaired about twenty of these LED bulbs, bought in China. It is exactly how you describe the defective LEDs, the burnt spot.... I also found some SMD resistors that were burnt out. I replaced them with normal resistors of the same value. Thanks once again for your efforts!
33gabor 7 years ago
33gabor
Yeah. But hereabout for 220V mains we mostly get cornbulbs fed throuh a nonisolated converter/rectifier modul, which itself unfortunately often causes the brakedown. These are hardly repairable economically.
Then, if the converter modul is still good, comes in the metod discussed in this article. In these bulbs there are 3 to 6 parallel connected "cob" strips. So the problem of tidy removal from an aluminium based stip of a bad LED still remais acute because a single LED is soldered to the strip surface not only at the ends but at its bottom also, to achieve faster heat transfer. So just this makes it difficult to unsolder.
What I wish to contribute to this article is that I "slighly" modified my wife's discarded household favorite, the electric iron. So that instead of 215 (for linen) now it heats up (adjustably to max 350 centigrade) and melts the solder of the strip all along. Now I just carefully remove the bad LED and place the new one. Also carefully take off the strip so that no other LEDs would get disturbed.
Good luck!
mrstan 7 years ago
karawin 7 years ago
Repaired: It was the 50R CMS resistor burned.
All leds was lightning but very low.
mrstan 7 years ago