16mm Sinkpad Help!

Hi guys,

I have just re-flowed an XML onto a 16mm copper Sinkpad. But now that it’s in the light the LED hardly lights up. What have I done? Pretty sure I have the + and - the right way.

Thanks

Marc.

can u post a pic ? did u check the driver if that had killed it

Hi Nitro,

I cant post a pic, sorry, I would have to borrow the wife’s camera. It was working before but not when I switched to a sinkpad. Strange. :frowning:

By the way it wasn’t from you, so don’t worry. It was a sample they sent me.

Marc.

Try connecting a battery directly to the LED momentarily and see if it lights up. That should tell you if the LED is good or not and you can work backwards from there.

that could easily toast the LED

I won’t do that then :open_mouth:

Marc.

Better use the continuity setting of a DMM, maybe you placed the LED wrong (pos and neg exchanged).

I have tested LEDs using a 3V 123A with no problems, just a 1 or 2 second burst of light will not damage the LED.

That’s what I thought, but I made a note of the + and - before I removed the LED and placed it on the Sinkpad, so I am a bit puzzled.

Marc.

impressive, so how did others on this forum toast their LEDs with direct connection?
Did you test 4.2V by any chance?

The voltage sag limits the current. Direct drive with a hot cell that doesn't sag under load as much (like INRs) is where the LEDs get killed. In the same way, multiple cells in parallel results in lass sag and the LEDs do not like that. They will even survive 2x cr123s in series... most of the time. I have killed one with that setup before, it worked fine for quite a while but eventually something glitched and took it out. I have never killed one with a conventional non-INR 18650.

Ok, I have put the LED together with another driver with the same results. LED is very dim but then flickers. This is the first time it has been used and looking back at what I have done the LED was the correct way round on the Sinkpad. So is it possible to just get a bad LED?

Marc.

Try re-heating the board until the solder melts, you don't need to remove it. If that doesn't fix it it's a bad LED (or it was damaged from too much heat during the first reflow, I have done that more than once). It won't light at all if it's a polarity issue.

continuity test can't damage the LCD, just try one way and if it does not work try the other way.

You have a red and blue (or black) probe, when (if) the LED lights up, red probe will indicate positive (+) contact...

Reflow the LED.

What I use to test LED’s is a cheapy radio shack AA battery holder with a not fully charged 14500 battery in it.

Just tapped the wires to the solder pads. Will let you know if it is reflowed properly. I had some that looked perfect but no light. Just reheated them on the stove and shazaam.

It sounds like one of the contact pads might not have connected up properly during the reflow. Do you tin the pads first, or just use the tinning that comes already on the sinkpad? I always add more solder to the contacts.

Yes, reheat it, when the solder isn't hot enough it does not 'retreat' to the separate solderpads fully and makes them short. When soldered well, the solder shines bright and smokes a bit, and the led snaps into place.

I had a similar prob with a reflow I did a while back and I think it was because the led was over cooked. It worked, but would never pull much current even on direct drive because the Vf was much higher. Replaced the led and was more careful with the heat, job-jobbed. :slight_smile:

Low temp solder paste is your friend while reflowing. Less likely to fry the LED.

Just my opinion. I would test the led with a 9v alkaline battery with one of these. The 9v can’t supply enough current to hurt the led. Its internal resistance is to high. There are two little pads on the led base that you can touch the wires to for the led test. If it doesn’t light decently bright, then its probably shot. If it does light up well, then its a bad connection from the reflow.
You might have to remove a small amount of silicone off those pads to get a connection.
.

I have had two reflows that I have done seem perfectly fine. Then once the light was operated for a good length of time went dim with flickering. In low mode it seemed fine but when switched to high it dimmed and flickered. I was sure something must have went bad with the driver. Until I tested the led at the base of the led with the 9v alkaline. My conclusion was that the reflow process had made the connection but not a good one. So I figured when the light got hot enough the poor connection broke and would not flow enough current for high modes. But in low mode there was just enough solder contact that the small amount of current flow worked fine. I reflowed the led again and applied a small amount of downward pressure with a carbon fiber arrow tube that I had laying around. Has worked fine ever since. Just my two cents. :slight_smile: