Is this how you test a Tl072 Op Amplifier

[rdhj]

Trying to figure out what is wrong with my DIY delay pedal and someone suggested my voltages at my TL 072 look way too low, so I looked on youtube on how to check it.  I put the multimeter on diode setting and put one lead on the output A pin and one on the input A as well as the other input A.  Did the same thing on the B side.  On the A side, the meter read 0.732 for both and on the B side it read OL for both.  Does this give any indication that the chip is no good?

[iainpunk]

using the diode measuring setting is not how you test an op amp, especially since an op amp is not a diode...

testing an opamp is simple, first there is the buffer method, for wich you need a breadboard and a (digital) multi meter.
configure the opamp in this configuration:

all the voltages on all the pins should be the same, if not, its probably bad.

if you want another method and you have an audio probe.
configure the both op amps in this configuration:

the audio probe should reveal a frequency near 1.5kHz on both the output and at a lower volume at the inverting (-) pin, if you can't get it to work, its probably broken.

i have a simple perf-board with two sockets for both methods, for both dual and singe opamp pinouts to test opamps i suspect to be wrong, but a normal breadboard is also a good tool to test opamps in a less permanent setup.

(now i think of it, this might be a good 'tool' to design a PCB kit for or something,)

cheers, Iain

[idy]

You set your meter to DC voltage, range just above your power supply,
on my meter 20v is the next value over 9v.

You stick (or clip) the black probe to ground of your circuit
and check the various pins with the red one.

If you are testing it in a powered circuit with 9v you should *usually* see:
0v on pin4
9v on pin8

all the other pins should *usually* read around middle voltage, more or less 4.5, although the inputs may be "loaded" by your meter and read a little low.

What circuit are you looking at?

[rdhj]

IDY...I was wondering if the TL 072 chip is bad for some reason based on the voltages I got before

[garcho]

You should have continued this in the first thread you started. The chances your delay isn't working because of a faulty op amp are very small. The low voltages around that op amp are clues to finding improper solder and wiring. Considering you're very new to this hobby, the chances you erred in your soldering are 99.9%. "Bad parts" make up about 0.1% of the problems around here.

[rdhj]

Garcho...i bet you are 100% correct in that today I took new readings and I was getting half of the input on most pins and one at 5 volts...i made an audio probe today and found i get audio in most plavces, some loud and clear and some not so clear.  Did see that some resistors have sound on one end but not the other..same with some other components.  I was trying to clean up the solder on my switch but not haveing much luck..wotking with solder is such a pain.  not having a schematic isnt making things much easier.

[rdhj]

Question for you all....when using an audio probe, should I get audio signals from every single end of every single component?  Or are there certain things that do not get tested with the probe?

[GibsonGM]

Question for you all....when using an audio probe, should I get audio signals from every single end of every single component?  Or are there certain things that do not get tested with the probe?

Well, you typically try to follow the signal path, and in time that will come fairly naturally.  If you probe power pins, you'll get a 'click' (provided you DO have a capacitor in your probe!) and then nothing as it blocks DC.   Ground same, as well as the leg of any component connected to power or ground.     If there is noise in your power supply sometimes you can hear that (if it's bad or a cap is missing or dead).

Otherwise, signal chain, from input thru the device to output > next device or effect out.   You'll get the hang of it...

It's also helpful to have a 'signal generator' for testing effects, which provide a signal so you don't have to pluck the guitar constantly (tho we all do sometimes).   That can be a simple oscillator, or even a recording from an MP3 player or some such thing.   Learn the probe first, next project, a simple signal generator

[antonis]

But it's always good to have a schematic/diagram to follow signal path.. 
(it should be more easy to locate "series" and "shunt" items..)

[Rob Strand]

Checking the DC voltages in the *original circuit* is often a good starting point for testing an opamp.   The original circuit *is* the test circuit so there's no need to specifically set-up test circuits.  If the DC voltages look OK it's highly likely the opamp is working and it's probably best to consider other avenues.   After that you can check AC voltage with a signal generator and oscilloscope - the step below that is testing with an "audio probe".

[GibsonGM]

Yes, what Rob says. My info was 'generic', answering your question about using an audio probe.  Voltages will tell you a LOT about the opamp your typical dirt box!    And quick & easy! 

[rdhj]

I have traced the audio signal from the input jack all the way to the Op Amp...Had to reflow some solder on a frew caps and resistors to get that far.  Only getting a signal from one pin on the amp and its not as loud or clear.  Is this normal.   I've been cleaning up joints alot but still no good.

[GibsonGM]

A lower signal on a pin that's used in the feedback loop can be expected to have a lower level; being present is what counts. But 'missing signal' at the other 2 would indicate either that the opamp is toast, or maybe something else isn't connected right.    Reporting what pin you get results on is traditional, so we can help you out more...       If you have a multimeter, this is a good time to just list the DC voltages at each pin, too! 

[idy]

Yes, you need to specify which pin you are measuring! And voltages!

My most common error is a biasing resistor not soldered well enough. It looks fine but the + input (3 or 5) is not getting its proper (middle, around 4.5) volts. So the op-amp does nada. You find a signal at pin 3 or 5 and nothing coming out...

Unless the op-amp is getting a proper DC voltage to that pin it will appear to be dead. I have experienced this too many times, and it has always been a resistor not soldered well enough. And the resistor always looks just fine even under a magnifying glass....

[antonis]

Are we talking about any particular circuit or we're just guessing..??

[garcho]

^ it's basically the PT2399 datasheet delay, some variation with a layout but no schematic, sold in kit form. For some reason the OP is resisting following the troubleshooting guide or much of any advice and being oddly parsimonious with any information, so good luck!

[Rob Strand]

I have traced the audio signal from the input jack all the way to the Op Amp...Had to reflow some solder on a frew caps and resistors to get that far.  Only getting a signal from one pin on the amp and its not as loud or clear.  Is this normal.   I've been cleaning up joints alot but still no good.

The lack of schematic makes is difficult to judge the results because it's not possible to see the "lay of the land" so to speak.

Here's a collection of common circuit patterns using opamps,

http://www.add.ece.ufl.edu/4924/docs/TI_SingleSupply.pdf

The circuits in figures 3, 4, 8 and 8 are pretty common.  Although you will often find R3 = 0. 

Unfortunately there's a few bugs  like the lower example in Figure 3.   The opamp + input should have an extra resistor to Vcc/2, more like Figure 6.  Also, it's common to put a cap in series with  R1 (those parts can then wire to ground or Vcc/2).

For the inverting amplifier case, top of figure 3, you would find the opamp+ pin and opamp- pin have no signal.   This is normal.  If you see signal on the opamp- pin the opamp could be clipping, so drop the test signal level.

For the non-inverting case, bottom of figure 3 + fixes, you would find the both the opamp+ and opamp- pins have signal.  In this case the signals are less than the output signal; as GibsonGM mentioned.

FWIW, the PT2399 chip has a number of opamps inside.   You need to get the datasheet to see what pins they connect to.

If possible try to trace out the circuit around the opamp(s) you think aren't passing signal.   Try to match-up the circuit with common circuits in the PDF link I posted.  Then try to judge what you would expect based on that circuit.    Without doing that it's very hit and miss because you don't know what you are dealing with and can't know what you should expect to see.

[rdhj]

I have been read trying to follow the debugging pages to the best of my ability.  Somehow, after all the messing with it and resoldering the joints, I actually got it to work.  However, when I hit the guitar strings harder or play a chord, I am getting a somewhat distorted sound, not clean like it should be.  Could this also be a bad solder joint that i didnt get yet.

[Rob Strand]

I have been read trying to follow the debugging pages to the best of my ability.  Somehow, after all the messing with it and resoldering the joints, I actually got it to work.  However, when I hit the guitar strings harder or play a chord, I am getting a somewhat distorted sound, not clean like it should be.  Could this also be a bad solder joint that i didnt get yet.

You did well pushing through.

Well, it is quite possible the units working and it just does that.    It's a bit of a fine line.   It becomes hard to judge without a schematic, or, without an oscilloscope to see how large voltages are before the circuit starts clipping.   You could keep pushing to see if you can improve things.

[Rob Strand]

FWIW, here's the what I understand is the original thread,
https://www.diystompboxes.com/smfforum/index.php?topic=126028.0

Possibly the TTone Delay kit.


There's this one called Tweaked Tone Delay
https://forrestwhitesides.com/tweaktone-delay/

Well it might be worth comparing against these,
http://revolutiondeux.blogspot.com/2012/01/mad-professor-deep-blue-delay.html
https://the7line.clan.su/_pu/0/92883033.gif

There's a gain of 2 before the delay and a gain of 1/2 after to improve the signal to noise.   Perhaps that's the cause of the overload.  Maybe pre-emphasis (boosting highs before) and de-emphasis (cutting highs after ) is a safer scheme to improve signal to noise with out risk of overload.    The inverting input stage might not be the best for that but anyway ...