Magic smoke and a burned out TL072

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artparks
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Magic smoke and a burned out TL072

Post by artparks » Fri Jul 24, 2020 5:52 pm

I just finished putting together a new case/DIY PSU (Metatronic Mods linear power supply) and painstakingly installing everything. Inevitably, I installed a module backwards (an ADDAC 200PI pedal integrator) and got the magic smoke, panicked and switched off. I checked it out, it seemed/looked OK so I checked everything else was correctly installed and switched back on. Left it for a minute or so and, puff, more smoke. But as well as smoke, my Intellijel ADSR went nuts too, with all the lights switching on. Panicked and switched it off again.

So I looked at the 200PI again and the op-amp on it is visibly fried (see picture) following its second adventure. My question is, what actually happens when an op-amp like this fries? My assumption is it was severely damaged from frying #1, limped on for a bit then fully exploded with attempt #2 (although it was round the right way this time!).

What would have happened that caused one frying module to affect another? The ADDAC module suddenly drawing lots of current so everything else struggles? The fuses on my PSU, 3A on +12V and 2A on -12V, didn't blow though, so it doesn't seem likely to have been that? But I don't see how one module meeting a sad demise would have caused the ADSR to panic. What's actually happening when this op-amp meets its demise?

I've checked all the other modules, plugging them in one at a time, and they're all still OK, including the ADSR. But I'm nervous to plug everything back in until I can kind of figure out how such a blow-out might have happened, and that I can solely pin the blame on the kaput op-amp and not some fault with the PSU.

Image

snowtires
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Re: Magic smoke and a burned out TL072

Post by snowtires » Sat Jul 25, 2020 2:57 pm

If there's a short to ground, there's a good possibility that it can affect the power and other modules, although I think most should have some sort of protection against it. I know I've put modules with a short into my rack and it's killed the power of the entire thing.

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Re: Magic smoke and a burned out TL072

Post by abelovesfun » Sat Jul 25, 2020 3:41 pm

Don't forget that flux IS conductive. It looks like there is quite a bit around the caps.
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Re: Magic smoke and a burned out TL072

Post by guest » Sat Jul 25, 2020 3:53 pm

if you reversed power on the module, a number of things could have fried, but things with silicon in them are the most likely, like your opamp. and since the transistors inside let current flow in one direction but not the other, the behaviour of your module can be different once its blown out and the power is put back to normal. its also possible for a module to pull enough current to pull down the powersupplies, but not blow the fuses. this is particularly true if there are current limiting resistors on the powersupply rails, or the voltage regulators themselves have current/heat protection built in. so long story short, its most likely just that module, and probably just the opamp. replace the opamp, and verify the module is working on its own before plugging it back into your rack.
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snowtires
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Re: Magic smoke and a burned out TL072

Post by snowtires » Sat Jul 25, 2020 4:43 pm

abelovesfun wrote:
Sat Jul 25, 2020 3:41 pm
Don't forget that flux IS conductive. It looks like there is quite a bit around the caps.
To that end OP, a toothbrush and rubbing alcohol will clean up most flux, just be liberal with the alcohol.

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Re: Magic smoke and a burned out TL072

Post by emmaker » Sat Jul 25, 2020 4:56 pm

abelovesfun wrote:
Sat Jul 25, 2020 3:41 pm
Don't forget that flux IS conductive. It looks like there is quite a bit around the caps.
???

Never had resistive issues with flux soldering for over 50 years. Some flux is hygroscopic and can absorb water and become conductive but I clean the water soluble flux soldering really well, don't worry about no clean flux solder and hardly ever use rosin core flux anymore. Dought this is going to effect anything here.

Some is corrosive, like never use acid flux on electronics and always clean water soluble flux.

Flux can effect some circuits with capacitance like S/H caps, caps in VCO integrators or high gain and/or impedance circuits. So you want to clean flux there. Typically that's in the pf range.

It's probably like guest said the op-amp has shorted out inside causing problems. Replace it and give it a try. Put it on a bench supply (if you have a bench supply that you can set current limits on all the better) to avoid frying something else, don't use your regular synth supply. Also any new module you build you should bring it up on a bench supply.

Jay S.

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Re: Magic smoke and a burned out TL072

Post by emmaker » Sat Jul 25, 2020 5:10 pm

snowtires wrote:
Sat Jul 25, 2020 4:43 pm
abelovesfun wrote:
Sat Jul 25, 2020 3:41 pm
Don't forget that flux IS conductive. It looks like there is quite a bit around the caps.
To that end OP, a toothbrush and rubbing alcohol will clean up most flux, just be liberal with the alcohol.
I'm more of a fan of using something to wick (Kimwipes) the flux immersed in the alcohol of the board. When I used a brush and alcohol I had to use a lot of alcohol to get all the flux off the board.



Jay S.

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Re: Magic smoke and a burned out TL072

Post by KSS » Sun Jul 26, 2020 12:34 pm

The remaning fibers in that preview photo -did not watch the vid- give me the willies.

Gotta be SURE those don't remain after any cleaning. Especially if they're cotton or cellulose based. I wouldn't want them there if 'plastic' either, but will concede that *may* be less a problem.

As for cleaning flux, put me squarely in the camp of YES. DO IT. Unless it's no clean, ALWAYS remove it as much as you can.

It's not the flux that's conductive. It's the stuff it attracts and holds. Much worse for classic 'Rosin' fluxes than some of those used today. But why play with fire? Except for no-clean type, Cleaning flux is part of the build.

It's worth pointing out that when we see photos online, what looks like sloppy flux might be no-clean. But it might also be some kind of conformal coating a mfr has applied that by design will not be a problem. Some conformal coatings look real ugly, and work really well. Seen them often on military jobs. but they're not unusual on other gear too.

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Re: Magic smoke and a burned out TL072

Post by artparks » Sun Jul 26, 2020 3:52 pm

emmaker wrote:
Sat Jul 25, 2020 4:56 pm
abelovesfun wrote:
Sat Jul 25, 2020 3:41 pm
Don't forget that flux IS conductive. It looks like there is quite a bit around the caps.
???

Never had resistive issues with flux soldering for over 50 years. Some flux is hygroscopic and can absorb water and become conductive but I clean the water soluble flux soldering really well, don't worry about no clean flux solder and hardly ever use rosin core flux anymore. Dought this is going to effect anything here.

Some is corrosive, like never use acid flux on electronics and always clean water soluble flux.

Flux can effect some circuits with capacitance like S/H caps, caps in VCO integrators or high gain and/or impedance circuits. So you want to clean flux there. Typically that's in the pf range.

It's probably like guest said the op-amp has shorted out inside causing problems. Replace it and give it a try. Put it on a bench supply (if you have a bench supply that you can set current limits on all the better) to avoid frying something else, don't use your regular synth supply. Also any new module you build you should bring it up on a bench supply.

Jay S.
I don't have a fancy bench supply but I do have a simple +/- 12v supply that I test things in isolation first with. I'm not a complete monster!

I'm sort of assured that it was this op-amp causing madness to flow backwards, I really can't see what else it was. I once read that TL072s were "built like tanks" but I guess that doesn't extends as far as several minutes of backwards voltages!

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Re: Magic smoke and a burned out TL072

Post by emmaker » Sun Jul 26, 2020 5:57 pm

KSS wrote:
Sun Jul 26, 2020 12:34 pm
The remaning fibers in that preview photo -did not watch the vid- give me the willies.
I think one of the points of the video was to show the different results with the different types of papers. I haven't had issues with Kimwipes. Sometimes I do some clean up with Q-tips and IPA which level more fibers that the Kimwipes. Once the board is dry you can take a brush and remove the fibers with that.

Good soldering.
Jay S.

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