I'm trying to find how i can test a schottky diode to check it's state but can only find info on 2 pin diodes. The particular diode is this: http://pdf.dzsc.com/2017/20161120/20161120081219688637.pdf

Am i correct in putting positive lead from multimeter to anode (pin 1) and negative lead to cathode (middle pin)....if i get a beep, it's working fine. i get no beeps, so is this diode dead?

the diode is part of a speed controller which isn't turning on.

if it's dead, is there any way I can bypass it to make sure the rest of the controller is actually working?

thanks, sal


If your DMM has a diode test function (diode symbol on the switch or display), try it both ways.

With the red on the anode it should show the forward voltage at a relatively low current, so maybe 250 (mV) vs. 600 or so with a regular diode. In the opposite direction it should show overrange.

Repeat the test for the other diode in the package.

Of course it needs to be removed from the circuit for this to work reliably.

A beep is not a good indication of semiconductor functionality- typically that means a short circuit, or at least a resistance that is fairly low.

  • \$\begingroup\$ i'm confused, my diode symbol on the DMM is under the 2k ohm setting..is that correct? when trying it on that setting with the red to anode and black to cathode, i get a reading of .300 and the other way round, i get over range. so that means it's working then? \$\endgroup\$ – Sal Apr 20 '20 at 19:24
  • \$\begingroup\$ Yes, then it's working. \$\endgroup\$ – Spehro Pefhany Apr 20 '20 at 19:37
  • \$\begingroup\$ right, in that case, i have no idea why my controller is dead! i can't see any blown resistors or caps or anything else for that matter. there are 2 relays which are working perfectly as well so i'm lost as to what i can try next! anyway, thanks for your prompt responses! \$\endgroup\$ – Sal Apr 20 '20 at 19:41
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    \$\begingroup\$ I guess it's some other part then. ;-) Bad parts sometimes reveal their state by appearance or odor but not always. Diodes are relatively rugged. If it's a speed controller and the power rails are okay, I would be looking at the SCR or MOSFET etc. that switches the motor because it is most stressed. \$\endgroup\$ – Spehro Pefhany Apr 20 '20 at 20:47
  • \$\begingroup\$ yeah there was a small odor but nothing major and all parts look brand new which is quite baffling. there are 4 capacitors and i really can't be bothered to unsolder them to check their ratings. \$\endgroup\$ – Sal Apr 20 '20 at 20:56

Choice A: Your multimeter has a diode test mode

If your multimeter has a diode test mode then you can check if the diode is good by seeing if the diode displays a typical diode voltage when forward biased (0.4V to 0.9V for your diode). To check this you’d connect positive terminal of multimeter to anode and negative terminal of multimeter to cathode. Then switch multimeter in diode test mode. If the diode is broken you should get either an OL indication or 0V.

Choice B: checking diode using Voltmeter mode and test circuit

If your meter doesn't have diode test capability then you can use it as voltmeter and use a test circuit. Consider the circuit shown below. Here you would have a voltage source with a series limiting resistor with diode under test. Here you simply measure the voltage across diode and if it’s working it would give a voltage of 0.4V to 0.9V. If it’s not working then you’ll see either 0V or OL indicator.

Consider using a 9V and 1k Resistor

enter image description here

image source : http://www.learningaboutelectronics.com/Articles/How-to-test-a-diode


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