Testing for OpAmps?

[iggy]

Thought I'd call on the experts here. Is there a way to test OpAmps, out side of a circuit? I built the Buffalo Pfuz and couldn't get a signal out of it. checked, rechecked all components, placements. Even probed the circuit. to no avail. Replaced most of the parts. no help. even swapped in a couple Opamps. got signal thru to the OpAmp input but no output. Finally found a opamp from a different manufacturer i had in a working pedal. popped it in and fired right up. I think i got a batch of UA741's from china that are either bad or not what they claim to be.

so. brings me to the question. how do you test these parts other than popping into a circuit & hoping they work.


BTW, after all that the Buffalo Pfuz....meeeeew.... gonna have to give it the Heath treatment.

[nocentelli]

This is the fancy method:

http://tangentsoft.net/elec/opamp-tester.html

A simpler way would be to rig the opamp under test to +9v and ground, link inverting input to output (I.e. a buffer), and put two resistors as a voltage divider on the non-inverting input (e.g two 100k, one from the input to ground and one from the input to +9v). Use a multimeter to confirm you have half supply voltage on the + input, and if the opamp Is working, you should get the same voltage at the output. You could then do a further check by adding an input and output cap, and playing guitar through it to check it's passing audio.

[Frank_NH]

Yes, it should be easy to rig up a simple tester which can check the DC gain in the inverting and non-inverting modes.  As Nocentelli's article suggests, you'd have to have one for single and one for duals (and for quads like the TL074).  

[iggy]

Thanks for the information. Hopefully that'll save me time with future problems. At least I got to work on  my troubleshooting technique with this one.