Snap-on LED Work Light Malfunction - Page 1
Forum section: electronics / repair

author: Smoky
author_rank: Frequent Contributor
timestamp: September 30, 2024, 01:28:58 am
content: I'm doing some foundation repairs and the customer let me use two of their work lights to brighten things up in the basement.One of them worked for about two hours and then started to flash on and off, and after a few cycles of this, the light doesn't want to come back on:All of the LEDs shined bright when it worked so it must be something on the board that has failed:The lights appeared to be in brand new condition but after a little research I found out that these were made around 2014 or so.The construction quality of the light is very good, thick glass, no burns on the board, so probably worth a little time and effort to fix it. Plus, it was free

author: Xena E
author_rank: Frequent Contributor
timestamp: September 30, 2024, 09:51:28 am
content: Quote from: Smoky on September 30, 2024, 01:28:58 amWhy would you draw that conclusion?Check the output from the board for a start, if there's nothing there, then it probably is something on the board. Otherwise LEDs can and do fail.Don't Snap-On do lifetime warranty on their products any more?X

author: Xena E
author_rank: Frequent Contributor
timestamp: September 30, 2024, 09:57:46 am
content: BTW.Did you have a premonition that the lamp was going to fail, and thought that you should video it?

author: Smoky
author_rank: Frequent Contributor
timestamp: September 30, 2024, 04:08:50 pm
content: There are 46 individual LEDs on the face of the panel so I couldn't imagine all of them failing at the same time so that's why I concluded that something wasn't right on the board.When I was troweling cement the work light started to go on and off so I picked up my phone to capture how it was acting up. I thought it would be a useful video while explaining the problem on EEVblog, my go-to place to get answers relating to electronics

author: jonovid
author_rank: Super Contributor
timestamp: September 30, 2024, 04:19:20 pm
content: this is a job for Big Clive channel YT

author: tunk
author_rank: Super Contributor
timestamp: September 30, 2024, 04:44:53 pm
content: The LEDs could all be in one (or maybe two) series andif one (or two) fails open then there's no light.Also look up the datasheet for the 8-pin chip to see ifit's a linear or switching driver.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 30, 2024, 06:15:31 pm
content: I used a USB microscope to look closer at the board and here you go:Look how the solder moved away from the pins of an MT7873 IC. It's definitely getting warm enough to melt solder. You can see browning of the PC board on the left side of it too.I took a slice of thin receipt paper and it slips right under one of the legs of the IC with very little effort:So the on and off of the work light was probably due to expansion and contraction and probably some arcing. Bad design? Needs more cooling? More robust parts?The 150uf/100v electrolytic capacitor measures good at 147uf on a Sencore LC-53 with 70 micro-amps of leakage tested at 100V.

author: Xena E
author_rank: Frequent Contributor
timestamp: September 30, 2024, 06:38:23 pm
content: Just looks like bad soldering. You've nothing to lose to tack the chip down again and try it.If it had been used at elevated temperatures for any time at all there would be more evidence of overheating.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 30, 2024, 06:47:02 pm
content: Nah, I don't think it's bad soldering. Imagine you have the light on for a while and the IC and the solder are getting hot during that course of time. Now, I accidentally bump the light while I'm working. This shock would splatter the solder off of and away from the pins of the IC like you see it in the picture and eventually cause it to malfunction. Just my guess.

author: Gyro
author_rank: Super Contributor
timestamp: September 30, 2024, 06:49:44 pm
content: Terrible reflow soldering. I'm just looking at the way C8 rotated during reflow due to badly designed solder mask. I would go around every SMD on the board.

author: Xena E
author_rank: Frequent Contributor
timestamp: September 30, 2024, 06:56:43 pm
content: If it's running at temps hot enough to melt solder it wouldn't last long, if you tack it down you'll be able to feel how hot it gets, assuming it works again. It just looks like a shitty assembly job.

author: Smoky
author_rank: Frequent Contributor
timestamp: September 30, 2024, 07:00:53 pm
content: Yeah, the leg on the IC that doesn't have a pad underneath is clearly up off the deck as if the IC was never resting down tight on the pads to begin with. But the way those two pieces of solder look to have slid away from the legs of the IC seem odd.Re-solder I will do

author: floobydust
author_rank: Super Contributor
timestamp: September 30, 2024, 07:27:29 pm
content: Caution - the LED's are hazardous live, this power supply does not isolate mains so there is a shock hazard.MT7873 Non-isolated LED CC Buck driver IC, it's got no thermal pad.Usually with chinese LED fixtures I will remove one (of the two) current-sense resistors to reduce power output as everything runs super hot. R6, R7 0.33R in parallel I think, so I would remove one and 1/2 the power for long life and cooler operation- if you see fit.Also I would inspect the LED's and look for the black dot of death inside, for ones that might be failing.

author: Xena E
author_rank: Frequent Contributor
timestamp: September 30, 2024, 08:43:38 pm
content: Quote from: floobydust on September 30, 2024, 07:27:29 pmYes! good call. you can often reduce the current by half with very little reduction in apparent light output.Quote from: Smoky on September 30, 2024, 07:00:53 pmCan't hurt to try, nothing to lose: if it's faulty and got so hot as to desolder itself you'll soon find out, it'll do it again or just not work.X

author: Smoky
author_rank: Frequent Contributor
timestamp: October 01, 2024, 03:14:03 am
content: I cleaned up the solder joints that looked suspicious and left the others that look clean and smooth alone. I find messing with old lead-free solder a pain. I use the lead+silver type and it's an absolute pleasure to use. The crooked capacitor Gyro spoke about is actually soldered-in very well and no need to touch it. The original electrolytic capacitor was put back in too. The brown area under the legs on the left of the IC is not burnt, it's actually just exposed PCB:I plugged the work light in and flicked the switch, and just like that, wham-o, I'm blind, I can't see!FloobyDust, resistors R6 and R7 happen to be a combination of .33 and .68 Ohms to ground. So is it as simple as removing the .33 Ohm resistor to lower the intensity of the light to roughly 70% output?Thank you

author: Smoky
author_rank: Frequent Contributor
timestamp: October 01, 2024, 06:41:08 am
content: Well, I removed one of the current sense resistors, the .68 Ohm one. The intensity of work light seems more comfortable now than before. Not blazing bright anymore but surely not 50% or less. It sure seems like 70% or so, but I'm still partially blinded from the last testSo what is the reasoning behind two sense resistors anyway? Install one first to get the lamp up and running and then a second to fine tune the brightness in front of a light meterThanks for the tip FloobyDust!

author: tunk
author_rank: Super Contributor
timestamp: October 01, 2024, 04:32:03 pm
content: The two resistors in parallel are 0.22 Ohm,so the output has been reduced by one third.The reason for using two is finetuning.

author: floobydust
author_rank: Super Contributor
timestamp: October 01, 2024, 06:09:12 pm
content: Removing just the 0.68Ω gives 67% of the original LED current. Something I would do if the board/LED's runs too hot. They seem to tweak the LED current to just below meltdown/achieve warranty period which is fine- but a fixture doesn't last.I notice if you drop LED current to 2/3 you don't get 2/3 light output - many LED's end up more efficient at a bit less than max. current and produce more light.So you might not have lost 1/3.That work light was rated 1,600 lumens/30W in and now is rated 2,000 lumens/25W which seems like a leap.

author: Xena E
author_rank: Frequent Contributor
timestamp: October 01, 2024, 06:15:42 pm
content: Quote from: Smoky on October 01, 2024, 03:14:03 amThat's a really super result! It's good when a well told story has a happy ending.Quote from: Smoky on October 01, 2024, 03:14:03 amIt would be great if you could take a picture of the label of this lead/silver solder of which you speak, it would be something that I personally would like to try if it's such nice material to use.Thanks in advance.X

author: Smoky
author_rank: Frequent Contributor
timestamp: October 02, 2024, 12:53:31 am
content: The problem with things I fix, especially when helped with tips and tricks that makes them better, is that I don't want to use them anymore, I just like looking at 'emOk, I'll use the work lights again but just not in crawlspaces anymore, maybe in an attic:Not long ago I bought a tray of 50 LEDs and I wasn't sure if I'd ever use them but the tray was under $5, how can you go wrong? Bridgelux BXRC-27G1000-B-73-SE. They're about 1-3/8" in diameter and run on a off-voltage (35v?) and wires just push into built-in sockets. But now I'm thinking they could possibly be mounted in work lights like these when their LED boards go badXena E, the silver solder is made by Kester, 24-7150-0018. I bought several rolls of these at the time because they were being dumped due to their old date codes. All I can say about this solder is that it just gets better with ageThanks for the help

author: Xena E
author_rank: Frequent Contributor
timestamp: October 02, 2024, 05:22:33 am
content: Quote from: Smoky on October 02, 2024, 12:53:31 amYes. I see .That is good stuff tin/lead 2% silver.If you're replacing lead free, clean as much off as possible before using that though. The alloy is produces if they mix can produce dry joints: But it looks like you've been successful.X