Newbie cracks open a CLM6000 . . .

[Gyoon]

Got one from smallbearelec.   I had to check to see if the LED was burnt out (appears to be the case).  I cleaned up some of the glue goop from the LDR side and held it up to a bright lamp.  The measured resistance was 2.2k ohms even though I got the one that was supposed to spec out at under 500 ohms.  Is there something wrong with the way I'm testing the resistance of the LDR?  Is there another, more accurate way of testing it to see if it works?

Glenn 

[smallbearelec]

I'm sorry you cracked it open before you let me know that the LED side was dead. I test those devices by connecting four penlight batteries through a 200 ohm resistor to the LED side, Under those conditions, the resistance should be under 500 ohms on the LDR side. As you were able to confirm that the LDR is good, you might want to pair it with a known good, high-brightness red LED, pot it or tape it, and so have yourself a working photocoupler.

[Gyoon]

I could have inadvertently burnt it out while installing it.  You're saying that that method is the most accurate way of measuring the LDR?  In EPFM I think Craig Anderton mentions that the exact measurement is not critical.

Glenn

[Paul Perry (Frostwave)]

I had a batch of old CLM600s once (some pretty far out of spec) & cracked one open for the LDR which happily was "just right" to replace a Morley wah LDR. I can only assume moisture got into the leds, I can't see what else vcould make an unused sealed led/ldr go "bad".

[smallbearelec]

I bought several thousand devices directly from Clairex before they stopped producing CdS devices. They were sold to me as "Untested CLM6000," and it was clear that I would have to do the sorting and qualifying. The test I described was Clairex's recommendation to put a 20 ma. forward current through the LED.

Some few of the devices gave no response from the LED when I tested them. All the rest fit the buckets that I show on the Stock List. It is true that the exact light resistance is not critical for most jobs, and a paralleled resistor can often be used to trim an otherwise marginal part into working correctly.

I recall having seen threads on this board about how to cobble a photocoupler, and you may want to search the archives and refer to those to help you create a working assembly.

SD