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BRG SMD LED's for festoons


cedd

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Hi all

 

Got a set of WS2801 festoons. Each "bulb" has a double sided pcb with 3 x SMD LED's on each side of it and a single control IC. The LED's are six legged jobbies not dissimilar from these;

http://www.farnell.com/datasheets/2046473.pdf?_ga=2.231626589.339246030.1544528663-1093368984.1480777934&_gac=1.229320360.1544548863.EAIaIQobChMIycLK66SY3wIVDEPTCh2yjQWXEAQYAyABEgK9lvD_BwE

 

A few of the "bulbs" have died on one side, but only for a single colour. Each side's 3 LED's are wired in series, and the 2 sides are in parallel. As I suspected, the failure is as a result of one of the LED's going open circuit on one of the 3 colours. I've been able to test this and identify the offending LED using a bench supply and touching the leads to the legs of each LED individually.

Now comes the tricky bit...

I thought I'd just be able to order a number of the above LED's and solder them back in place. I've now realised that these LED's are a different colour order to the standard ones as shown above. The Kingbright (and indeed seemingly every other 5050 LED) ones are RGB when counting from pin 1/6 upwards. Mine are BRG.

 

I've tried for the life in me to source replacements but am really struggling. They were manufactured in China by a company who sell nothing but LED's, so it's not beyond imagination that they're cooking their own. Really hoping that's not the case though!

Anybody out there got any thoughts?

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I do a lot of designs with 5050 type LEDs from different manufacturers/suppliers and have had the RGB pins turn up in every order imaginable. My software now has a #define to sort it out.

 

It can be hard to find out what the colour sequence is at the ordering stage, but you can definitely get them with other varieties than RGB. I will have a look through and see if I can identify suppliers, back shortly

 

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Thank you Tim

All my Arduino stuff also has definable RGB order for just that reason. I'd just fix it in code but sadly here the other side of the PCB that's still working won't match. I've wondered about some sort of physical adaptation I could make to switch the order around, and then back again for the other LED's. Possibly a tiny pcb that sits in place with the RGB LED on top, or something similar.

I've trawled Alibaba and Aliexpress etc. but it's tricky to find.

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Thanks to Tim’s help I now have 20 working pixels ready to either go back in to my remaining strings as spares, or to build a new string with when I get the time. I also have a burnt thumb, but that’s what you get trying to do SMD with a normal iron too much. There was me thinking I was proficient at soldering!
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You're implying that I did the work at home where I have the ability to buy things like that, rather than on the work bench at work http://www.blue-room.org.uk/public/style_emoticons/default/rolleyes.gif

 

But yes in all seriousness I'm trying to persuade the boss to buy us a reflow station at the minute. Mainly so I can repair my own stuff, but we do occasionally have to fix handheld radios that actually belong to work too!

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I would be wary trying to hot air reflow 5050 LEDs, I have had a lot of trouble with them not working after soldering due to moisture in the LEDs. As far as I can tell you get a pocket of steam inside the resin of the LED which can break the little bond wires.A quick touch with a soldering iron seems to work much better.

 

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I would be wary trying to hot air reflow 5050 LEDs, I have had a lot of trouble with them not working after soldering due to moisture in the LEDs. As far as I can tell you get a pocket of steam inside the resin of the LED which can break the little bond wires.A quick touch with a soldering iron seems to work much better.

 

Hmm. I'm maybe going to have to experiment with that. I store all my bulk LEDs in a dedicated sealed box with a humidity meter and desiccant blocks to keep then dry. In the early days of LEDs there were definitely thermal/moisture problems that caused damage.

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