Repair LED circuit board on expensive lamp - Page 1
Forum section: electronics / repair

author: Hatmpatn
author_rank: Newbie
timestamp: January 12, 2022, 07:21:00 pm
content: Hello! A family member bypassed the power supply and connected 230V line directly to the LED board on a ceiling lamp.I'd like to repair this, and I want to find a replacement for the two black components on the board.Next to one component it says "D1" and on the other it would appear to say "TZ1". Dont know what TZ1 stands for.On the D1 component it appears to say "S21 GP 051""On the TZ1 component it appears to say "YP 0AA"Any idea what easy-to-get components I can switch these out to?

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 12, 2022, 07:58:50 pm
content: Are you sure the LEDs survived?

author: fzabkar
author_rank: Super Contributor
timestamp: January 12, 2022, 08:01:23 pm
content: I suspect that "YP" is a zener and "S21" is a Schottky diode. The zener would clamp the maximum forward voltage, while the rectifier would divert reverse voltages.STPS2H100A, STMicroelectronics, 100V, 2A power Schottky rectifier, marking S21, SMA:https://www.st.com/resource/en/datasheet/stps2h100.pdf

author: abdulbadii
author_rank: Frequent Contributor
timestamp: January 12, 2022, 11:56:05 pm
content: diode to half rectifyTZ is DZ ie. zener for smd comp. Look uphttps://www.sos.sk/pdf/SMD_Catalog.pdf

author: james_s
author_rank: Super Contributor
timestamp: January 13, 2022, 12:52:50 am
content: I would expect some if not all of the LEDs have blown too. It's hard to tell from the pictures but it looks like there are black spots in many of them.

author: floobydust
author_rank: Super Contributor
timestamp: January 13, 2022, 01:24:19 am
content: I don't think the LED board is repairable. Many LED's show the "black dot of death" which means they are burnt. Test them and see if the LED's survived, but it does not look good.

author: james_s
author_rank: Super Contributor
timestamp: January 13, 2022, 04:04:56 am
content: Technically you could replace the LEDs, using a hot plate it might not be too hard, but it's still a pretty fiddly job.

author: fzabkar
author_rank: Super Contributor
timestamp: January 13, 2022, 05:43:08 am
content: Could "TZ" be a transzorb?SMAJ36A, Vishay, transzorb, bidirectional, 36V, marking YP, DO-214AC:https://www.farnell.com/datasheets/548547.pdfSMAJ36CA, Littelfuse, TVS diode, bidirectional, 36V, marking YP:https://datasheet.octopart.com/SMAJ58CA-Littelfuse-datasheet-10313496.pdfThis is a 400V device, so it is probably unsuitable:SMAJE400A, Bussman, TVS diode, bidirectional, 400V, marking YP, SMA:https://www.eaton.com/content/dam/eaton/products/electronic-components/resources/data-sheet/eaton-smaje-tvs-diode-power-esd-suppressor-data-sheet.pdf

author: Hatmpatn
author_rank: Newbie
timestamp: January 13, 2022, 09:37:45 am
content: Thank you for all the good tips!I think I might go ahead and order these then:I applied 2,5V directly on some of the diodes just to test them and they behave somewhat differently. Im afraid some of them are bad.

author: Chalcogenide
author_rank: Regular Contributor
timestamp: January 13, 2022, 09:48:19 am
content: If many LEDs are damaged, depending on how expensive the lamp is and how willing you are, you could design a new aluminum PCB and have it fabricated; then you could populate it and solder yourself, but you are going to need an oven or a really good hotplate to reflow the LEDs onto the aluminum pcb.

author: james_s
author_rank: Super Contributor
timestamp: January 14, 2022, 02:24:11 am
content: You can also buy similar LED boards direct from China. I don't know if you'll find one that is a direct fit but you might get lucky or at least find one that is close enough and has similar electrical requirements. Test the LEDs before you bother replacing anything else.

author: floobydust
author_rank: Super Contributor
timestamp: January 14, 2022, 02:48:06 am
content: I don't find MCORE pc boards easy to repair - you heat the entire board up, or not. These LED's would have thermal pads.So I could not see a way to heat up only one or a few LED's, they're all mounted to the one heatsink.

author: james_s
author_rank: Super Contributor
timestamp: January 14, 2022, 03:00:30 am
content: You heat them all on a hotplate and then replace those that need it.

author: floobydust
author_rank: Super Contributor
timestamp: January 14, 2022, 06:39:07 pm
content: But how long do you have, the LED's at solder melting temperature? Then you have to cool off the hot plate and mcore, I didn't think LED's would give you much time. They have softer epoxy and fragile I find.Example fromCree 5630 datasheet:Liquidus Temperature (TL): 217°CTime (tL) Maintained Above TL: 60‑150 secondsMight be possible to heat up the board and pick off the bad LED'sBut pretty much all of them have a black dot so I would only use the board for practice.

author: TheMG
author_rank: Frequent Contributor
timestamp: January 15, 2022, 03:54:15 am
content: Most likely all the LEDs are dead (the little black dots are a sure sign). If obtaining a replacement board or retrofitting something else in is not an option and you REALLY want to repair this one, I'd throw it on a hotplate to melt the solder and wipe ALL the components right off the board. Then let it cool, apply solder paste, populate it with all new components, and reflow solder.