Testing op amps - Page 1
Forum section: electronics / beginners

author: mattybigback
author_rank: Contributor
timestamp: December 15, 2013, 11:49:48 am
content: Hi thereCan anyone recommend a way of testing an op amp to see if it's damaged? I made a noob mistake while breadboarding a circuit and I think I might have fed voltage to the input of an op amp. Ever since doing that my circuit isn't working as it should, and having changed the transistors the only other component that could be knacked is the op amp.Also, would blowing one op amp in a quad pack (TL-074) make the others useless?

author: fcb
author_rank: Super Contributor
timestamp: December 15, 2013, 12:35:08 pm
content: Don't ever feed voltage into an opamp...Test it with a very basic G=1 voltage buffer configuration, that should give you a degree of confidence.As all the opamps in 074 share the same die, it's quite likely that you'll kill more than one, especially if it's an overvoltage situ.

author: Bored@Work
author_rank: Super Contributor
timestamp: December 15, 2013, 12:42:02 pm
content: Just replace it, don't waste time and money testing it. If the circuit works after you replaced the opamp you knew the old one was broken.

author: SeanB
author_rank: Super Contributor
timestamp: December 15, 2013, 01:04:11 pm
content: Simple test is place finger on opamp with power on. Finger not hot= possibly working. Finger hot=possibly dead. Finger has imprint of part number burnt into it=Dead Jim.If possibly working or possibly not check supply voltages. As it is a quad opamp check each stage, +input voltage, - input voltage and output. + & - should be close to each other ( less than 10mV) and output should be somewhere between V+ less a volt and V- plus a little. If they are at rails then Dead Jim. Use meter with high input impedance, if inputs have resistors under around 20k then a 10M meter will do.As it is a jellybean opamp easiest to do if it is Dead Jim or it seems suspect is to replace with another. If it is a DIP part and you just want to see cut the leads off flush with package plastic and slip the new one temporarily into the socket now there to check quickly. Then you can do the desolder of pins and solder in new or just solder the stubs to the new if you are in a hurry. Done that on boards where you could not get to the bottom at all unless you started at one end of the board and removed a line of DIP packages till you got to the one you wanted and had a vapour phase reflow bath to redo all the solder paste to put them all back.

author: WIRENUT
author_rank: Contributor
timestamp: December 15, 2013, 01:12:31 pm
content: I would definitely replace the chip and see what it does to the circuit, its the fastest way. OpAmps are cheap enough to just replace. Always a good idea to get two of every IC in a circuit under test just in case. That is of course if it is cheap.

author: Sigmoid
author_rank: Frequent Contributor
timestamp: December 16, 2013, 05:28:24 pm
content: I can only second FCB. Set up a simple noninverting voltage follower on a breadboard, and see if it "follows".http://en.wikipedia.org/wiki/Operational_amplifier_applications#Voltage_follower_.28unity_buffer_amplifier.29(Do make sure to insert a resistor into the feedback line, to protect the pin. It is not necessary on most modern chips, but it's still a good idea.)

author: M0BSW
author_rank: Frequent Contributor
timestamp: December 16, 2013, 05:35:03 pm
content: http://www.bing.com/images/search?q=op+amp+tester+circuit&id=943B5120CC26A7F1070D44606495A12C8398D7C3&FORM=IQFRBA#view=detail&id=1610F046A15D9C7F1CFFE49E63B5AA5121E5286C&selectedIndex=15

author: cristoper
author_rank: Contributor
timestamp: December 16, 2013, 07:34:08 pm
content: Here's a nice little op amp tester you can build:http://tangentsoft.net/elec/opamp-tester.html