UV LED Device Repair

[dennis_elx33]

Hello Guys,

Part Name: UV LED 365nm
Problem Statement: LED intensity low

I am repairing a UV LED lamp device. Found to have multiple burnt devices though I cannot identify what is this. Highly suspect that it is a resistor or a diode but i could not fully identify it because both resistance and diode test got OL result.

Is there anyone here who knows what is it? or how can i test it?

[stj]

Re: UV LED Device Repair

are the leds in series?

[dennis_elx33]

Re: UV LED Device Repair

Hello stj, yes, the leds are in series.

What is the best way to check this unknown component?

[stj]

Re: UV LED Device Repair

check a good one as a diode and see what the meter does.
i am thinking it could be one of 2 things
it could be a diode to protect from reverse polarity,
or it could be a special device that bypasses dead leds.
https://www.littelfuse.com/industrie...rotectors.aspx

[dennis_elx33]

Re: UV LED Device Repair

Hi stj, sorry for the very late reply..

I measured the unknown component using diode mode but there is no reading at all even forward and reversed bias. So do you think it is a special device instead of a diode?

[harp]

Re: UV LED Device Repair

Maybe to check know good component with zener tester. It use higher voltage (can read higher voltage drop) and constant current.

Is any reading of resistance, or capacitance can measure when desoldered from pcb? If it is a very high resistor, say 100M that is over range of your multimetar, you can do a trick: use 9v battery and see in voltage mode can it pass any voltage
Or
Use as much biggest resistor you can read with your multimeter (say 40M) and add this in parallel with it, then calculate resistance.
Also, can you get picture of good component, not burned one, maybe some sign on it, or side shape...

[stj]

Re: UV LED Device Repair

i have never seen one of those led protectors, i have no idea how they react to test equipment

[eccerr0r]

Re: UV LED Device Repair

kinda doubt a completely open circuit would cause low intensity...

Could you show a zoomed out picture of these elements with how they're connected with its LED and other LEDs? And perhaps others of the same element?

Zener diodes should be a regular diode in one direction and seem to usually fail short.

And as far as I can gather from the photos these are parallel with each LED? Did all of them burn?

[harp]

Re: UV LED Device Repair

Some link info

https://www.techbriefs.com/component...articles/14277

https://cieonline.co.uk/led-shunt-pr...lity-lighting/

[CapLeaker]

Re: UV LED Device Repair

almost looks like a LED driver like an AL5809?

[eccerr0r]

Re: UV LED Device Repair

harp is probably correct, this is for protecting against dead-open LEDs that would cause the whole array to go dark, So because of these failures probably a lot of the LED chips on that board probably have already failed with these devices and likely the whole board is probably ready for the scrap heap...

[dennis_elx33]

Re: UV LED Device Repair

Hi harp, really sorry for the very late reply. Been to other more urgent projects. Anyway, i have a photo attached here. As for your suggestion, i will try to do it. Thank you so much!

Hello eccerror, i couldn't identify if its parallel or series but the unknown devices (black color) are all open reading.

[dennis_elx33]

Re: UV LED Device Repair

Hello All,

One more problem is that i could not remove it using 2 soldering iron and even with the use of low temp soldering lead..

Also, tried to use a hot air blower but all unsuccess to remove.

And to make things worse, it is so fragile that even poking slowly by a tweezer, it breaks!

Any suggestion on this?

[harp]

Re: UV LED Device Repair

Yes, it is on huge heatsink... preheating will be required in order to desolder it.
Kitchen pot heater on bottom side (lowest temp about 150 - 180 dec C) and two solder iron/hotair from top side? It is heavy task...

And now I see... no nozzle, or at least no small nozzle! Max temp, max air... but before, remove board from device, it is actively cooling down from bottom side.

[CapLeaker]

Re: UV LED Device Repair

Should have used low melt solder first, then preheat then take it off with an 80W soldering iron with a wide tip.
Max air and max heat on the reflow station just burns stuff… at least mine does.

[dennis_elx33]

Happy New Year everyone!! Please be informed that I was able to remove the unknown chip by using a pre-heater and wait for the PCB to heat up until around 150C. But the weird thing is, up until now, I'm still confused as to what part is this. Though I highly suspect it is a diode because it can light up the LED when ever i probe on the forward bias (possibly) and LED wont light up when reversed. The odd thing is that I could not see any voltage drop on both forward and reversed bias. The only indicator i can say is lighted LED. Need your expert advise on how can i test or prove what component is the SMD chip is. Thank you so much! -- This idea is credited to Harp and all of you guys who gave their inputs!!