Replacing SMD LEDs in a lamp - Page 1
Forum section: electronics / beginners

author: steradian
author_rank: Newbie
timestamp: April 25, 2020, 07:02:23 pm
content: I'm putting together an electronics workbench and today received an LED task lamp. Its color temperature and CRI are unfortunately awful, so I want to replace the SMD LEDs. I have decades of through-hole experience, but have never attempted rework on this type of component. I have a brand new Quick 861DW hot air station that hopefully will be useful.I found a YouTube video that showed someone heating the PCB from below, and that makes sense as the top of the LEDs are much more susceptible to heat damage. But beyond that, I'm not sure what the best way is to proceed. Any and all tips would be much appreciated.

author: jmelson
author_rank: Super Contributor
timestamp: April 25, 2020, 07:19:31 pm
content: WOW, that is a LOT of LEDs. Now, you have to get them ALL oriented with the right polarity for it to work. That gives you a lot of chances for error.Assuming you want to reflow all the replacement LEDs in one step, you need an oven that can rapidly and evenly heat the whole board. You needto apply just the right amount of solder to each solder pad, place the LEDs and then reflow it. That sounds really complicated.I built my own lighting retrofits, see :http://pico-systems.com/Lighting.htmlAnd I hand-soldered each LED to the PC board. This was somewhat tricky, but I had pretty good results with it. I think my LEDs are running more current (350 mA) than in your fixture. Your fixture looks like it might have 90 LEDs in one series string, as I don't see any resistors.Jon

author: mikerj
author_rank: Super Contributor
timestamp: April 25, 2020, 07:42:05 pm
content: You need the check the original LEDs to ensure there is only one LED die within. Plenty of mains powered LED lamps use parts that have 2-3 dies in series in each package.

author: steradian
author_rank: Newbie
timestamp: April 25, 2020, 08:02:17 pm
content: Thanks for that excellent piece of information. This might not be a viable project.

author: Marco
author_rank: Super Contributor
timestamp: April 25, 2020, 09:22:57 pm
content: Why not just fill it up with some decent CRI led strip instead? (Not that I know where to get that for cheap.)Not the greatest efficiency, but you can fill up the shape of the lamp nicely.

author: james_s
author_rank: Super Contributor
timestamp: April 25, 2020, 10:06:52 pm
content: Most of these sort of things use aluminum core boards that will really suck the heat up. The easiest way to reflow is to use a hotplate to heat it from below. Seems like a lot of work though vs just buying an LED strip with the color you want.

author: steradian
author_rank: Newbie
timestamp: April 25, 2020, 11:18:15 pm
content: LED strip reels are pretty expensive from the manufacturer, and the mechanical build quality of the lamp really doesn't make it worth doing for me.It looks like my idea wasn't a very good one, but that's fine. I've learned a lot quickly today. I found a Japanese task lamp that uses the manufacturer's LEDs so I'm buying that and returning the unacceptable one.

author: james_s
author_rank: Super Contributor
timestamp: April 25, 2020, 11:54:15 pm
content: Those strips do seem quite expensive.Another option which I've done in the past when I wanted a custom arrangement is to buy some inexpensive screw-in LED bulbs that made good quality light and then take them apart. The LEDs are usually mounted on an aluminum plate that you can mount on your own heatsink. The lower cost bulbs are less likely to have the driver circuit potted.