Is my LED light broken?

Thread Starter


Joined Oct 19, 2021
Hello - I am building an LED lighting application using a COB LED light similar to this one:

I've been troubleshooting why the LED light is not turning on when I connect it to power and it seems the LED light itself is broken. As you can see from the picture, there are positive and negative terminal pads on the COB LED. I used my multimeter (switched to Ohm mode to measure resistance) and when I connected the multimeter leads to the COB LED light, it showed OL or overlimit resistance even at the highest Ohm measurement level (20 Mega Ohms).

I believe this means there is no connection between the positive and negative pads of the LED light and therefore the LED light is defunct. Is my reasoning correct? It's strange since this is a brand new COB LED light.


Joined Dec 2, 2017
Makes much more sense to check the voltage across the COB, even in diode mode the meter will not produce enough voltage to get a reading. (COBs with a forward voltage of 34 will have multiple LEDs in series)

How are you driving the COB?


Joined Jan 27, 2019
As others have said, LEDs (which are diodes) do not behave like ordinary resistors, so if you try to measure the resistance through them the results will be confusing.

Diodes conduct only in one direction, and even in that direction they will not begin to conduct until a certain voltage is present. Your DMM uses a very low voltage to test resistance (which is a goo thing!) and it would not be sufficient to forward bias a single LED and cause it to conduct.

Since your COB is certain to have many LEDs in series, the voltage required is the number of LEDs multiplied by each LEDs threshold voltage. This is why one white LED might turn on at 2-3V but the COB needs much more before illuminating.

If you have a variable power supply, you can do a simple test which will tell you if the COB is working (though not necessarily that it is not).

  • Set the power supply to a low voltage, say ~5V and turn it off.
  • Connect the power supply to the COB carefully observing the polartity, this is important!
  • Confirm the positive and negative connections are to the correct terminals
  • Dim the lights in the room so you can see any activity on the COB
  • Turn on the power supply, nothing will happen
  • Slowly adjust the power supply voltage up, at no time exceed the specified supply voltage of the COB
  • Watch for any of the chips on the board to begin to glowing, it is normal that some will light before others

If you see any of the chips glowing your COB is working, if by the time you get to ~50% of the specified supply voltage none of the chips are glowing, something is wrong. If you think it is possibly that you have the posit i’ve and negative terminals wrong, you can try again with the connections reversed.


Joined Apr 5, 2008

How are you powering the led?
The page you show does specify this:
Current - Test : 550mA
Voltage - Forward (Vf) (Typ) : 34.4V
Current - Max : 1.05A



Joined Mar 10, 2019
Like other mention, that is a 36V LED. You need at least 36V to turn it on, and a few hundred mA of current. Maximum current is 1300mA for that device if you keep it at 85C or less, but you have to consider heat dissipation - you may need a good heatsink.