How to diagnose an opamp is broken  - Page 1
Forum section: electronics / beginners

author: hp3310a
author_rank: Regular Contributor
timestamp: November 26, 2024, 05:51:39 pm
content: Hi,is there a simple way to tell an opamp is faulty? I've managed twice to kill an opamp by mistake - maybe due to incorrect connections including of power supply lines, maybe due to ESD, maybe due to disconnecting of power while the signal was still turned on.In both cases it didn't occur to me that the sudden strange behavior of the circuit that worked just fine yesterday is because the opamp is dead. Exchanging the opamp eventually fixed the problem, but I had no way to verify it is dead. I would be great if there was a way to tell before I go and solder another $10 opamp onto a new prototyping SMT adapter.The opamp in question in my case is the AD8034 (data sheet herehttps://www.analog.com/media/en/technical-documentation/data-sheets/AD8033_8034.pdf)

author: schmitt trigger
author_rank: Super Contributor
timestamp: November 26, 2024, 06:54:34 pm
content: Wire it as a unity gain buffer, and on the noninverting input connect a potentiometer such that you can vary the input voltage from Vcc to Vee. Monitor the output, it should follow the input, as long it meets the I/O limits.

author: fzabkar
author_rank: Super Contributor
timestamp: November 26, 2024, 07:21:27 pm
content: A quick in-circuit check would be to verify that the inverting and non-inverting inputs are equal, if the op amp is in its linear operating mode. A typical failure mode is when the inputs or output are stuck at ground (single supply) or the supply rails (single or dual supply).

author: xvr
author_rank: Frequent Contributor
timestamp: November 27, 2024, 12:16:08 pm
content: Just a note -QuoteAD8034 is a FET input opamp. Using it solo in SMD prototype adapter is a fastest way to kill it - it very ESD sensitive device.Add a pair of back-to-back diodes across opamp inputs and high valued resistors from input to ground and between power rails. It will help opamp survive been soldered on adapter

author: BILLPOD
author_rank: Frequent Contributor
timestamp: November 27, 2024, 01:42:55 pm
content: Good Morning Hp3310a, I too have murdered many an op amp, so instead of soldering it directly to a board, I solder in a socket and plug the op amp into the socket. Easy to swap out with a known good one.

author: hp3310a
author_rank: Regular Contributor
timestamp: November 27, 2024, 03:59:42 pm
content: Thanks everyone for your suggestions. Turns out I only murdered one of them and the other is still working. The issue seems to be that I get a lot of high power noise into the opamp input and that's what causes the malfunction of the rookie circuit. Before this began it worked fine and I have no idea what I changed that causes this.Quote from: xvr on November 27, 2024, 12:16:08 pmI would love to do that if only I understood how that is supposed to work. Wouldn't that connect the inputs to ground via one of the two diodes depending on the polarity of the signal?Pretty sure that's not it, but what is it then?

author: xvr
author_rank: Frequent Contributor
timestamp: November 27, 2024, 04:06:17 pm
content: No, between inputs (+ and -). It will limit differencial voltage

author: hp3310a
author_rank: Regular Contributor
timestamp: November 27, 2024, 04:43:01 pm
content: Quote from: xvr on November 27, 2024, 04:06:17 pmOK, thanks! But...Quote from: xvr on November 27, 2024, 12:16:08 pmThat's not all I didn't understand apparently. I still don't understand the emphasized portion of your suggestion.

author: xvr
author_rank: Frequent Contributor
timestamp: November 27, 2024, 04:45:08 pm
content: This is a path to ESD discharge through resistor, instead of internals of opamp

author: hp3310a
author_rank: Regular Contributor
timestamp: November 27, 2024, 05:08:21 pm
content: OK, thanks, I think I understand.