Dead emitter?

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Sirstinky
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Dead emitter?

How can you tell if you’ve killed your emitter? I’ve had a heck odd a time today with that. I got a new driver from mtn the 17mm fet+1, with Crescendo (awesome when I got it going), but I couldn’t get the darn thing to work. I got this driver because I killed the A6 I was using as a tester for a project. I shorted the output at the led on accident and the driver wouldn’t go out of moonlight. I got this new one yesterday. I thought the new driver was was bad, but put it in another light and it works fine. The driver I took out of that donor isn’t working either. A I checked the led on my multimeter in diode check and shows 2.5v? Should be 3.something, right? I tested it by directly connecting it to an 18650 and nothing. No light. Battery reads 4.08v.

bansuri
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I use a CR2032 battery to test mine. Not enough juice to damage it if you reverse polarity. An 18650 hooked straight up seems like it could cause trouble either way you connect it.

whatsthepoint
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If you have a voltmeter put it on the continuity setting and put the leads on the + and - of the mcpcb.

If good the LED will light up.

This is also done after reflowing new LEDS to mcpcb boards to test if done correctly.

never underestimate the power of stupid people in large groups

Henk4U2
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If you test the led be aware that it only lights up in one direction, so please try it both ways.

Lights like the S2(+) have little room between the ledboard and the back of the reflector.
So if you accidentally have a solder blob on the ledboard that’s just a fraction too thick,
you short the driver, and the led. Both will survive, for a few seconds.
Try lowering the solder blob or put a piece of kapton tape between ledboard and reflector.

You are a flashaholic if you are forced to come out of the closet, to make room for more flashlights.

Sirstinky
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Thanks for the suggestions. I am thinking the emitter is toast. I checked it on the continuity test and the diode test again and nothing.

Henk4U2
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You never know when it is finally too much, but diodes can take a heavy beating.
Did you do the test on a ledboard just lying on the table or still sitting in the light.
If the latter is the case, un-solder the red lead, because the driver interferes the test.
And dim the lights in the room, if the led tests OK it will not emit a bolt of lighting.

You are a flashaholic if you are forced to come out of the closet, to make room for more flashlights.

Sirstinky
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Henk4U2 wrote:
You never know when it is finally too much, but diodes can take a heavy beating. Did you do the test on a ledboard just lying on the table or still sitting in the light. If the latter is the case, un-solder the red lead, because the driver interferes the test. And dim the lights in the room, if the led tests OK it will not emit a bolt of lighting.

I tested it with the mcpcb lying on the table not connected to aything. The continuity test shows open circuit and the diode test is ‘ol’. I tried connecting the 18650 (an old Samsung 26Q that’s pretty tired) with test leads and nothing. No light.

Any ideas? I find it hard to believe the emitter is toast as it hasn’t been abused at all and it hasn’t really been used.

kamots
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What is the forward voltage of the LED? Maybe it is above 6 volts and you just aren’t driving it enough?

The meter I use has a 14V diode test, maybe yours does too? It is usually something you need to toggle on.

moderator007
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Its possible it has a bad reflow (solder isn’t connected to the mcpcb pads). The only way to be sure is to unsolder it off the mcpcb and test it using the actual led pads.
I have used a 9v alkaline battery to test with. The 9v alkaline battery can’t deliever enough current to do any harm. A DMM continuty test works well if the DMM puts out enough voltage to light the led. I believe I have owned a cheaper one that didn’t have enough voltage to test with.

Sirstinky
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kamots wrote:
What is the forward voltage of the LED? Maybe it is above 6 volts and you just aren’t driving it enough?

The meter I use has a 14V diode test, maybe yours does too? It is usually something you need to toggle on.

It’s a 3v xhp50.2 I know the vf is around 3.1 or so. My multimeter has a good diode test and will light up white LEDs (sst40) okay, but I never tried a working xhp50.2 3v to see if it will work. I tried in continuity and the dedicated diode test.

Sirstinky
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moderator007 wrote:
Its possible it has a bad reflow (solder isn’t connected to the mcpcb pads). The only way to be sure is to unsolder it off the mcpcb and test it using the actual led pads. I have used a 9v alkaline battery to test with. The 9v alkaline battery can’t deliever enough current to do any harm. A DMM continuty test works well if the DMM puts out enough voltage to light the led. I believe I have owned a cheaper one that didn’t have enough voltage to test with.

True! It might be my dmm can’t light the xhp50.2 3v. It will a SST-40 though. The led had bean working previously, but it mysteriously died after I fried the A6 driver.

How do you test it if you define it from the mcpcb?

moderator007
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First unsolder it from the mcpcb then flip it over on the dome. Use the continuity setting check between anode and cathode, try both ways of polarity if you dont know which one is what.

.
If your DMM lights up a sst-40 in continuity mode it should light up a 3v xhp50.2
If it doesn’t light up at all, its toast! Wink
.
I’m not very clear on if you have had this particular led working or not, so I’m wondering if it’s possible you have a 6v xhp50.2.
My Dmm doesn’t work on 6v leds. You might try a good 9 volt alkaline battery to elimate the possibilty. If it doesn’t light up with that then it is definetly toast.
.
Well, I see where you said it was working previously, wouldn’t hurt to try the 9 volt anyway.

Sirstinky
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Thanks for the tip! It was working previously on 3 volts so I know it’s not a voltage issue. Both drivers I tested it on are good as well. I double checked the driver without the led attached and it registers direct drive off the battery, which seems normal. I’ll desolder it from the mcpcb tomorrow and test it. I ordered another led this evening so if it works after desolder then great, I’ll have 2 xhp50.2’s! How often do mcpcb go bad, if ever? Is that possible?