any idea regarding lmc 567 testing

[tedsorvino1]

Hi everyone.
Some years ago I had built this simple ring modulator pedal based around an LMC 567 and a TL 071 and it worked well the few times I 'd used it. https://www.instructables.com/id/Ring-Modulator-Pedal/

Unfortunatelly I tried to check the circuit the other day and suddenly it became dead. I checked all the connections and I carried a test around the ICs (the rest of the parts seem fine) using my signal generator (1V sine wave signal ) and oscilloscope and I realised that the signal is nearly lost (a very low voltage square one) on pin 2 of LMC 567.
Is this normal? How can I tell if the IC is good? 
Unfortunatelly I haven't got a spare one to test.

I also checked the op amp (TL 071), I found that it was burnt and I replaced it with a spare one I had TL072 (using just one of the two op amps). Better result on that side of the circuit - so presumably the op amp works well -  but still the signal coming in from LMC 567 is way too low.
I have to add that when the op amp is connected my power supply shows that it feeds the circuit with 4mA but when it is not and I just feed the LMC part of it it shows around 0 - 1 mA.
I may managed to fry both ICs since the original op amp found dead.

Thanks in advance for any info or advice

Ps. Is there any really good tested Ring Modulator lay out or schematic that you propose?

[GibsonGM]

One way to test that chip is to look at the data sheet and build one of the circuits in the Application Notes, which should work fine.   If it works from a simple app. note circuit, chip is good.   I see a couple there that should do the trick, esp if you have a scope.

Opamps are easier, you could even build a dedicated board to pop the common ones of same pinout in to test.   

I have a simple thing I built for 555 timers that just flashes an LED if the chip works (LFO).   

This may help:  http://web.mit.edu/6.115/www/document/lm567.pdf


EDIT:  Aieee, ok, I see it's an SMD tiny thing, like this?  http://www.ti.com/lit/ds/symlink/lmc567.pdf

In that case, I'd see if there's a way to make an easy circuit to pop it into - but that will take creativity on your part so as to be able to get it in/out without ruining it.     Given the low cost of these things, if it doesn't work with a known design and you're suspicious, I'd trash it! Sorry.

[tedsorvino1]

Thank you GibsonGM for the advice.
Unfortunatelly mine is a different chip - that's what my circuit demands. It's this one.

http://www.ti.com/lit/ds/symlink/lmc567.pdf

and the TI test circuit seems much more complicated to the one you suggested - I wil try it anyway to see what's going on.
Could you please send me a schematic - lay out for the opamp tester?
Best regards.

[GibsonGM]

Hi Ted, yes, I re-read your post and I see that your LMC is SMD, which is too bad because the larger IC's are easier to test  

To test an opamp, you need to simply build a small circuit with a socket so you can swap out the chip.  A small AC amplifier, for instance.  This will give you a "go, no-go" indication of if your opamp is working.  Of course you must match the pinout of your device, and also would differ for single or dual opamp. 

I will sometimes open a pedal I've built and swap, say, a dual opamp (TL072, 4558 or other w/same pinout) and see if it works. It may be SLIGHTLY different in sound, but it will show function.   If you need an actual circuit, look up "op amp basic amplifier" on the web, there are MANY easy circuits out there!

There are some 'empirical' tests you can also do:  https://circuitdigest.com/forums/analog-electronics/how-check-if-my-op-amp-damaged

HTH!

[tedsorvino1]

Thanks Mike for the info on the op amp testers.
On the other hand my chip it is not an SMD. It's a normal 8 pin one but of a different type. Not LM 567C but LMC 567 (different characteristics). But the test that TI gives is really complicated.

[GibsonGM]

I hear you Ted!  I can't find anything simpler that will allow you to test it...I thought it was SMD, not familiar with the "LMC".  Looking around, it seems like that might be the one you need to use.  If you look around more, you might find something simpler to just see if it WORKS - the datasheet example seems like a pain, yes!

[anotherjim]

On the LM567 datasheet, there are some oscillator application designs that use few components. If the VCO won't produce a tone, then the whole chip probably is dead. The LMC567 should work in those applications. If you're sure the op-amp got killed, then there probably isn't much hope for your 567.

Chances are, it's had a reverse polarity power connection. It's very easy to try to clip a battery on reversed which with modern high power batteries can easily blow things on the board. Or if using a 2.1mm DC jack, use it with the wrong polarity on the plug. Most of us build in protection diodes in the boards' DC power supply input to prevent damage -  even if the published design doesn't.

I see a flaw in that circuit anyway - the opamp output directly drives the pair of diodes to ground with only the impedance of the output capacitor to limit the current. This can cause the op-amp to overheat or blow the diodes.

[GibsonGM]

I see a flaw in that circuit anyway - the opamp output directly drives the pair of diodes to ground with only the impedance of the output capacitor to limit the current. This can cause the op-amp to overheat or blow the diodes.

I never opened that schematic....now that you mention it....a 10k resistor in series at the opamp output might be a good idea, and make that 100k pulldown 10k...needs some messing around with.

[tedsorvino1]

Excellent advice from both of you guys. Pressumably the IC is nearly dead (I will try an easy LM  test even if I know that it produces a tone, but a very low one). I think I have to try a new one when I will be able to find one. And I will place the resistor on the op amp. Thank you.