Hi

Not sure I am missing something here, I have been renewing some smd LED's on strips rom a TV back light array, have completed 7 , doing the last 2 ( 1 each on separate strips ) , but there seems to be a problem with the polarity , as you can see in the picks , the base of the LED's have 2 surfaces for soldering, a broad surface and a narrow surface, on the back light strip's the broader surface is the +, but the broad contact on the LED is showing positive, when I soldered the first 7 I just soldered broad surface to the positive and tested each one after soldering and each one was ok, but tested these 2 I have left and it wouldn’t light, so ad to remove them both to see why, very, very strange , I don't know what to do now, I can't solder them has per what the polarity is because the contacts will short !.

Help.
Cheers

Spike

 

Honestly these things are so fussy to solder the first time that any rework is bound to lift pads.

Just buy another set off Ebay.

 

I see red and black meter probes.
What type of meter are you using? Is it a digital multimeter or an analog multimeter?
The two meters have different polarity when measuring resistance.

 

Hi
I probably have not explained it properly for you's to understand, I have already de-soldered and soldered new ones back on strip (x5) it is quite easy using a hot plate, in answer to Mr Chips the 2 probes are not from a meter (well they were!) they are just supplying 6v DC to the chip, they are a double led chip.

Maybe the next attached pics may explain my conundrum, the large area contact base on the chip is Positive, but the large area contact point on the strip is Negative, I didn't check the ones I have done because they tested ok after soldering.

Hoping the pics will give you some idea has to what I am trying to say.

Cheers

Spike

 

Did you buy your replacement LEDs from a reputable source? Could they be factory rejects because of a polarity error?

 

Did you buy your replacement LEDs from a reputable source? Could they be factory rejects because of a polarity error?

Hi
Yes that is exactly what they are spot on

 

Maybe the next attached pics may explain my conundrum, the large area contact base on the chip is Positive, but the large area contact point on the strip is Negative,

I use a LED strip, actually a double strip with white LEDs one side, and RGB LEDs on the other. To power these there is a 12V input, and you ground each of the remaining four lines to turn on each color.

So naturally, the input tabs are marked GND, 12V, G, R, and B.

12V is where you input the 12V power. Similarly, R is where you apply ground to turn on the red LEDs.

However, you ground G to turn on the blue LEDs, and B to turn on the greens. That of course leaves GND to turn on white.

I believe the moral of the story is not to depend on people who don't speak English as a native to get the nomenclature correct. Or even close.