testing optocoupler

[kardenm]

And finally (well, maybe not), is it possible to test an "optocoupler" #PC123Y11 ??

[BobA]

See Link

Your particular IC has 4 leads so you do not have access to the base of the transistor.

[lilshawn]

see your other post...

[MonMotha]

An optocoupler is basically an IR LED and a phototransistor inside a package with the LED pointed at the transistor photo sensitive base.  They're difficult to fully test except to simply test overall functionality.

You can at least check that the input LED isn't blown by using a multimeter on diode check.  It should read about 1.2-1.7V forward and much higher (usually 10+) reverse if it doesn't read open.  If it reads shorted (~0V) in either direction, very high (>2.2V) forward, or low (<5V) backward, the LED on the input is probably blown up.  The input LED is usually what goes for me, so it's a valid check.

Checking the output transistor is a lot harder since there are often hidden diodes and resistors, and there's no exposed base.

If you'd like to do a functional test, it's not that hard, but I'd probably want to draw up a circuit rather than try to describe it.  Probably easier to just replace it if suspect.  They're not expensive.

[kardenm]

Mine test open (over limit) in both directions (using diode test on LED side).  I guess that means it's bad.  Right?

Thanks for the info.

[BobA]

If you are open both ways on the input LED side then it is kaput.

[kardenm]

Thanks all. 

I'll keep plugging away at this one.  May take me a while to get a replacement.