LED mains bulbs repair - Page 1
Forum section: electronics / repair

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 17, 2021, 03:37:06 pm
content: Looks like all of Mains LED bulbs (even those sold with western brand names) originate from the same Chinese factory and last less than the good old CFL bulbs do (probably even filament incandescent ones) and they almost always fail the same way, one of the series LEDs fail. I opened one (see pic) and noticed (as I expected) one of the LEDs have a black dot when they are connected to mains, and that same LED measures 49V while the other LEDs are 7.8v dc.Assuming that the one that measure different (much higher) is the faulty one, then what options do I have for replacing it? Anyone knows what kind of LED takes 7v8?How about putting a resistor, a diode, a transistor/zener/resistor combination, or even a short in the bad LED's place.

author: Gyro
author_rank: Super Contributor
timestamp: May 17, 2021, 03:59:36 pm
content: Take a browse through some of Big Clive's videos, he has reverse engineered and modified (for lower output / cooler running) lots of low cost LED bulbs over the past year or so...https://www.youtube.com/user/bigclivedotcom/videos

author: tunk
author_rank: Super Contributor
timestamp: May 17, 2021, 05:25:19 pm
content: Most likely there's three LEDs in each package.I think you (temporarely) can short it to see if it works.You could also replace it with e.g. a 100ohm 1W resistor.Or you could try to hack it to lower wattage and longer life:https://youtu.be/5HTa2jVi_rc

author: Alti
author_rank: Frequent Contributor
timestamp: May 17, 2021, 06:43:32 pm
content: Quote from: Vincenzo on May 17, 2021, 03:37:06 pmTake it back to the seller, it is his problem and his money. I have not seen an LED that does not advertise "lasts longer than incandescent", most likely you were mislead.

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 18, 2021, 07:23:50 am
content: NOTE: This message has been deleted by the forum moderator Simon for being against the forum rules and/or at the discretion of the moderator as being in the best interests of the forum community and the nature of the thread.If you believe this to be in error, please contact the moderator involved.An optional additional explanation is:

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: May 19, 2021, 09:19:50 am
content: I repair these all the time. Usually mode of failure is one LED failing. They are connected in series, so the lamp goes dark or flickers. The black dot on the yellow substrate dot is typical for the faulty ones.Just use a lab power supply set to 30mA constant current with some probes to test them individually.Put the PCB on a hot plate (using a soldering iron on these aluminum PCB does not work well) and replace the bad chip.Measure the current and voltage on a known good sample to identify the LED. You can find the LEDs on Ali, Evilbay etc. Example:https://www.ebay.de/itm/224072197741

author: jonpaul
author_rank: Super Contributor
timestamp: May 19, 2021, 10:02:31 am
content: We use Phillips and Sylvania LED MR-16 at 12V, 120V and 240V.Very reliable and great color/efficiency. Never had a failure in mnay years (but bad fixture socket contacts...)Unsure the factory loc but sold all over EU and USA.I would avoid any noname Chinese junk.Jon

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: May 19, 2021, 02:34:16 pm
content: Quote from: jonpaul on May 19, 2021, 10:02:31 amI agree completely, but throwing OSRAM or Philips LED chips at lamps that are Chinese garbage to begin with may be putting lipstick on a pig.Failing LED Lamps are 99% junk from my experience. If you plan to repopulate the entire board, go with the quality stuff.

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 19, 2021, 09:39:13 pm
content: Quote from: Gyro on May 17, 2021, 03:59:36 pmThank you, sir. I don't know how I missed this video during the thorough search that I did. It is exactly what I was looking for. It took me several times repeating it, though, because of the funny way he speaks (my be due to a very bad family dentist). There is another dude who thinks he's big and speaks even funnier (that one humiliates himself, makes himself a joke, because there are no English teaching screw-ool where he lives, and he's obsessed with cheap chinese markers!!).The bulb in front of me has a 3-pin little IC that is different (PM9003A) but is almost identical otherwise. It looks like each little square is a few LEDs in series and can be replaced with a tiny little 2N2222 or similar with a couple of resistors configured as a Vbe multiplier (to take the same voltage and current) soldered as a "dead bug" or in the air and the main SMD resistors to be manipulated to lower the power to make it last longer.

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 19, 2021, 09:55:29 pm
content: Quote from: tunk on May 17, 2021, 05:25:19 pmThank you, sir, for the two suggestions. I'll do the second and the first (100Ohm, 1W R) is an even easier but less scientific way than a Vbe multiplier that I intend to add (more flexibility)

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 19, 2021, 11:52:04 pm
content: Quote from: BreakingOhmsLaw on May 19, 2021, 09:19:50 amThank you, sir, for the effort of a really useful point. I love your user name. It's a good reminder that "Ohm's Law" is only a small signal approximation in most situations and was called a "LAW" by what the late prophet George Carlin used to call Symbol-Minded.First, I guess a few mAs In-circuit application is valid in this case, I'll report to you when I do that, even though I can tell from voltage measurement in all 17 LEDs, in addition to the tiny black dot that you mentioned too which one (and only one, as you referred to and as I can see in the case in front of me) is bad.How hot is a hot-plate supposed to be here? Not looking for a number with fractions, but is it as hot as deep frying on the hot plate (real hot, red) or barely ON?And before doing that, how do you even take the aluminum/PCB out on the first place? (there are 4 supply pins that are holding it to the base that are not soldered but attached using black magic)I think it's not worth all that effort anyway, and just shunting the bad LED-rectangle that is bad with something is adequate. Thanks to you now I know that they call them "SMD LED 2835 Chips" and it's good to have 100 for future repairs(5 cents a piece) but still the choice of voltage and color needs some thinking.

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 20, 2021, 12:04:16 am
content: Quote from: BreakingOhmsLaw on May 19, 2021, 02:34:16 pmThat's it.I made up my mindI'll be rich in no timeFirst thing I'll do (EE dreams) is I'll buy me a Trump tower and fill it with tektronix zillion GHz scopes that sing songs and Fluke meters that flyAll by starting a small business repairing Walmart bulbs

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 20, 2021, 02:00:48 am
content: If you insist on fixing a led bulb I think the most pragmatic route is to simply short the bad one and reduce the current some so the remaining LEDs hopefully live.

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: May 20, 2021, 09:15:44 am
content: Quote from: Vincenzo on May 19, 2021, 11:52:04 pmI usually set the hot plate to 180 degrees. That way, the components stay fixed until you touch something with an soldering iron. Lead-free tin starts melting at around 200 degrees.You do have to remove it entirely from the lamp so it sits flat on the heating plate. Usually there are wires soldered directly to the PCB. If you can't remove it non-destructively, shorting a single LED may work if the power supply is designed to generate a constant current. But in cheapo lamps, that is not always the case.

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 20, 2021, 10:06:37 am
content: Quote from: BreakingOhmsLaw on May 20, 2021, 09:15:44 amyou got numbers for me..do you have an accurately temperature controlled hotplate?I am definitely going to stick something across it, but this knowledge is very interesting for the future.BTW, how do you quote only one sentence from someone's reply?

author: BrokenYugo
author_rank: Super Contributor
timestamp: May 20, 2021, 05:55:59 pm
content: If you can get the lamp running I've seen Big Clive use the LEDs to preheat the board sufficiently. Of course all precautions apply here as these things are generally mains referenced.

author: james_s
author_rank: Super Contributor
timestamp: May 20, 2021, 07:23:54 pm
content: Quote from: Vincenzo on May 18, 2021, 07:23:50 amWhy would anyone want to make obsolete filament bulbs again? I phased those out over 20 years ago, they make reasonably good heaters though. Incandescent lamps are not coming back, LED is here to stay, and it works fine if you get reasonably good quality bulbs.Buy good LED bulbs and they last, I have lots of them in service for close to a decade now. If you buy crap they will fail, and if you repair crap bulbs they will fail again. Cheap bulbs are a false economy, spend just a little bit more and get bulbs that live up to their stated lifespan claims. Also contact GE and tell them your bulbs failed early, there is a very good chance they will send you some more bulbs at no cost with no hassle. Sylvania sent several boxes of free bulbs to a friend of mine after he complained that a box he got didn't last.

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 20, 2021, 11:21:43 pm
content: Quote from: james_s on May 20, 2021, 07:23:54 pmWith all due respect,Are you a corrupt politician?Just keep your eyes on the AZ canvassing,We'll make her great againAnd "emotionally" destroy the planet with all the polar bears and commiesIf you are not, then, I want you to know that I buy walmart 40 bottle packs of drinking water as much as i can afford and empty the bottles in the river just to make more plastic waste and "kill" the planet

author: james_s
author_rank: Super Contributor
timestamp: May 21, 2021, 03:05:18 am
content: Quote from: Vincenzo on May 20, 2021, 11:21:43 pmI'm not really sure what to make of that gibberish but you do you, I'm not going to tell you what to do, if you want to spend your money to make a mess just to spite other people that's your prerogative. I have no connection to the lightbulb industry, I just understand math well enough to correlate what I spend on electricity to how much I consume and more so in the summer when I'm paying for energy to pump excess heat out of my house. I phased out incandescent over 20 years ago when CFL became affordable because despite shortcomings it was so much more efficient and I was an early adopter of LED bulbs back when they cost me $40 *each* because I could see the clear advantages offered by the technology compared to CFL. Those early expensive bulbs paid for themselves a long time ago and most of them are still in service. A few I've replaced not because they failed but because bulbs with nearly double the efficiency became available with better color rendering too. Even ignoring the energy consumption, I *really* don't miss the nasty surprise of flipping on on a light late at night to have it go POP with a blinding flash.

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 21, 2021, 04:47:47 am
content: I'm fully aware of everything you're saying, sir. But the nostalgia is invaluable. I have been to the museum in the NJ town of Edison, and it was one of the best leisure activity I have ever done. Besides, we were talking about repairing LED bulbs (which means we're using them) and about the electronics circuits and tricks, not to solve my personal problem with lighting options. Anyhow, I apologize if my humor was a little too extreme.

author: coromonadalix
author_rank: Super Contributor
timestamp: May 21, 2021, 05:14:27 am
content: Leds have quality grades ... i worked for a company in the past who tried to sold Chinese led bulbs while cutting the prices.The weakest ones in the loot (pcb with serial or parallel leds) will fail and kill the bulb, tried a few times to save them, ended trashing them, sometimes its the leds quality or the led driver(s) quality ... mostly the capacitors fail over time.If by chance you can grab a super led of say 10x10 or 15x15 array leds, try to power it little by little while augmenting the voltage, you may or will see some leds working differently on it, some will lit before the others, if its the case, you have a bad quality led

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 21, 2021, 09:08:17 am
content: Quote from: coromonadalix on May 21, 2021, 05:14:27 amIs there any bulb in the solar system that is not made in China? Did you mean that there are non-chinese bulbs?I did figure own how to accomplish my American dream and get filthy rich (and probably purchase Gate's wife) by starting my walmart LED bulb repair business and giving infinite warranty by tweaking the components and lowering the LEDs' current.

author: Gyro
author_rank: Super Contributor
timestamp: May 21, 2021, 06:04:51 pm
content: Quote from: Vincenzo on May 19, 2021, 09:39:13 pmClive lives in Scotland and so he speaks with a (perfectly normal) Scottish accent. I think the other guy you are talking about lives in another European country.For the uneducated, these are places outside the US.

author: Vincenzo
author_rank: Regular Contributor
timestamp: May 22, 2021, 04:25:29 am
content: Is that close to Arizona and stuff? I knew they have very bad dentists down thereThey need to find better gigs till they find better dentists and do some implants and crowns or somethingThat's Fourier's law for for you, it's how the world works, from the east coast to the west coast, all 50 states

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: May 23, 2021, 09:08:07 pm
content: Quote from: james_s on May 20, 2021, 07:23:54 pmReally?

author: Gyro
author_rank: Super Contributor
timestamp: May 23, 2021, 09:28:28 pm
content: That's rather an edge case don't you think?It's not long ago that fridges and microwaves used filament lamps too. Those are LED these days. It's just a matter of time, proper design, thermal insulation and ventilation.You could argue that a filament lamp in an electric oven doesn't affect energy consumption anyway.

author: james_s
author_rank: Super Contributor
timestamp: May 24, 2021, 04:56:19 am
content: I do use a filament lamp in my oven, that's one application where it makes sense, and even though it's a gas oven the heat given off by the lamp is not wasted and it's on very few hours. Incandescent appliance lamps are still readily available specifically for that reason.