how test an optocoupler?

[juh]

I have several P521 opto isolators from defective power supplies. I researched how to test them. Pin 1 and 2 are connected to a LED which means I can test them like how I test a diode. Whenever I place the black probe of my multimeter to the cathode and the red to the anode, I get a reading about 6 mega ohms. When I switch the probes, I get more than 20 Mega ohms. is that normal? All the eight opto isolators i've tested show the same results. I wonder if they are all working good or if they are all defective. thank you so much for your help!

 

[(*steve*)]

Measure the resistance across wherever you get the high resistance and inject 10mA into the LED. The resistance should drop significantly. If it doesn't, try try reversing the connection.

Even better, look up the datasheet

 

[juh]

Thank you. But where can I get a 10mA source? Sorry, I'm new to this. Tnx!

 

[(*steve*)]

Click on tutorials above ^^^ and select the tutorial on LEDs. Use the calculations there to determine the correct resistor to use with whatever power supply (perhaps a 9V battery) you have.

 

[KrisBlueNZ]

http://www.google.com/search?q=how+to+test+an+optocoupler