how to tell whether an op amp is burned out?

[tasos]

you know op amp get destroyed too easy...here is a thought...if you are giving voltage to v+ but not getting voltage when you measure the other legs of your op amp...would this show me whether it is burned out?any other suggestions?

[Gurner]

Here's how I do it .....I drop in another in it's place (cos for example, a TL074 is only about 20p)

If I then start getting an output ....then the previous opamp was Donald Ducked.

Seriously....sometimes it's difficult to establish whether an opamp has blown internally ...ie often there's no external indication (though a finger on top "ouch" test sometimes yields results!)

[Johan]

measure the DC voltage at the +input. then measure the DC voltage at the output. if the results are significantly different, the opamp is most likely shot. if they are the same, the opamp is most likely ok and the problem is something else.
J

[Mark Hammer]

Op-amps can sometimes appear to not be functionig properly, simply because the legs/pins are not making good contact with the socket.  Obviously, this does not apply if the op-amp is soldered properly to the board (i.e., no cold joints).  But if a socket WAS used, it can happen that a pin gets bent under the chip in a way that is hard to spot.  It can also happen that the pin makes poor contact with the socket.  Sometimes it pays to simply remove the chip, check for bent pins, give the pins a light scraping with a utility knife to make them look shiny again, re-insert, and make sure the chip is seated properly such that the socket and chip pins all line up right.

[R.G.]

measure the DC voltage at the +input. then measure the DC voltage at the output. if the results are significantly different, the opamp is most likely shot. if they are the same, the opamp is most likely ok and the problem is something else.
J

Almost.
(1) the power supplies have to be correct first; measure the voltage on the V+ pin and the V- pin. The V+ pin must be significantly more positive than the V- pin for the opamp to work correctly. in 9V effects, you'd expect V+ to be about 9V more positive.
(2) the output must not be loaded too heavily. The simplest way to ensure this is to open the circuit out of the output pin to the next part. Obviously, if the output is shorted or otherwise overloaded, it **can't** be operating correctly, and worse, your meter can't tell.
(3) there must be DC feedback from the output to the (-) input pin. The simplest way to ensure this is to short them.
(4) there must  be a DC voltage on the + pin which is roughly in the middle of the power supply pins. Without this, the thing may not operated even close to correctly. This voltage should be supplied through a resistor a lot lower than your meter's input impedance; otherwise, you will read the voltage on the + input incorrectly. Use resistors below 100K to make sure.

When you have all this verified, measure the voltages on the (+) input, (-) input, and output. They should all be within a few millivolts of each other and the power supply pins should remain as in (1). If this is not true, it's toast.

This got complicated as I wrote. That's because opamps are very flexible in application - which is just another way of saying that there are a lot of ways to make it do things you don't think you've told it to do.  

I've had bad opamps happen to me - but only a handful in using thousands over the last few decades. I've messed up hooking up opamps and used them wrong thousands of times. Note the statistics.

[R.G.]

'Morning Mark. You posted as I was typing.

Yep, what Mark said too.

[Gurner]

I should say that opamp failures are only common whilst I'm in a breadboard frenzy...sometimes, it only takes you to be out by one row (parallax error!) & it's goodnight vienna!

01.30hrs (GMT)  tends to be peak "burn an opamp time" in the Gurner laboratory.

[tasos]

ok...i use an ic socket...but it is perfect soldered and it's pins contact the circuit[dmm continuety test]my ic is pt2399...it has a lot of outputs...which one will i use for the output to do measurement's?pin 16 probably?

[R.G.]

ok...i use an ic socket...but it is perfect soldered and it's pins contact the circuit[dmm continuety test]my ic is pt2399...it has a lot of outputs...which one will i use for the output to do measurement's?pin 16 probably?

So you are wondering if you killed the opamp inside a PT2399? Is that correct?

[tasos]

i wonder if i have murdered pt2399...at pin 16 i get no sound..... i don't know if you have seen this topic...http://www.diystompboxes.com/smfforum/index.php?topic=89137.0  but i always wanted how to test whether an op amp is dead...what do you think?is it murdered?

[anchovie]

In a problem-free circuit you should see 2.5V at pin 16 of a 2399 (you should see the same at Vref pin 2).

Here's what you need to do:

• Check the 2399 voltages (all pins - you should have posted these in your other thread without asking)
• If the voltages are confirmed as wrong, remove the 2399 and check if audio gets as far as where pin 16 would be
• If there is audio up to that point, try another 2399 in the socket and see if it works
• If it doesn't work, another part of the circuit is built wrong

[tasos]

i am so sorry...here are my voltages
pin 1: 4.92v
pin 2: 2.45v
pin 3,4: no reading here....
pin 5: i don't get a number...it turns around all the way up and doown from 0.49v to 4.21v...
pin 6: 2.47v
pin 7,8: no reading [but these are grounded so..]
pin 9 to pin 16: 2.46v

[anchovie]

i am so sorry...here are my voltages
pin 7,8: no reading [but these are grounded so..]

3 & 4 are your direct connections to ground, 7 & 8 have capacitors.

All of the PT2399 opamp voltages are fine (from your first post, I thought you meant you had 0v somewhere on pins 9-16). Take the 2399 out and probe for audio on socket pin 16.

[tasos]

ok..i removed the chip and i get signal now at pin 16!i put it in again and i get no signal!

[anchovie]

Can you confirm that you didn't ground pins 7 & 8 directly?

If all is good with the chip connections, its time to try another chip.