Burned something, help in recognizing what to replace!

[Pancra85]

I built this circuit on PCB:




Tested it and worked ok. After putting it on a case by mistake I miss-connected GND and VCC, it was only for 3 seconds and it smelled burned circuit...
I want to know if just by looking at the schematic it's easy to detect what has been burned and needs to be replaced.

Thanks!

[armdnrdy]

it was only for 3 seconds and it smelled burned circuit...

Do you know how long 3 seconds is? 3 seconds is 3 billion nanoseconds! One nanosecond is to one second as one second is to 31.7 years.

In terms of reverse polarity...That's long enough to probably burn up the op amp. (IC1) Is it socketed? Try changing it out with any general purpose dual op amp.

[armdnrdy]

It looks like Guitar Gadget's minor inprovements to R.G. Keene's Simple Mixer could have used a minor improvement in the reverse polarity department.

[Pancra85]

In terms of reverse polarity...That's long enough to probably burn up the op amp. (IC1) Is it socketed?

Yes, I have socketed it. I will try replacing it then.

What about the polarized capacitors? they don't get burned if inversely connected?

It looks like Guitar Gadget's minor inprovements to R.G. Keene's Simple Mixer could have used a minor improvement in the reverse polarity department.

hahaha, I hear you.
Right now I was doing some research in this and it seems that a series diode will be the simplest solution, the problem is that I don't know if the loss in voltage that it causes will be too much for the circuit to work, what do you think?

[armdnrdy]

I was just writing to tell you to check the polarized caps as well when you posted. It seems if those went you would have known it.

[Pancra85]

I was just writing to tell you to check the polarized caps as well when you posted. It seems if those went you would have known it.

I am veeeeery new at electronics so no... I really didn't know. Ok so, I will replace the caps first and if it doesn't work I will also replace the IC.

Thank you very much!

[armdnrdy]

I don't know if the loss in voltage that it causes will be too much for the circuit to work, what do you think?

This is a pretty basic circuit. Throwing in a 1N4001 or similar diode won't pose any harm.....in fact, it just might protect from harm!

A 1N4001 has about a .7 volt drop. You could do worse from low batteries and the circuit will still work.

[armdnrdy]

I'm screwing this quote thing up as you can tell from my last post.

Do you have access to a meter? If so, lift one side (If that's possible) of the cap to check it.

[Minion]

(psu bypass) caps will generally fail by exploding , but even if the caps failed the circuit would still work so I would replace the Opamp first and if it still doesn't work then I would look elsewhere for the problem .......

[Pancra85]

Do you have access to a meter? If so, lift one side (If that's possible) of the cap to check it.

No I don't 

(psu bypass) caps will generally fail by exploding , but even if the caps failed the circuit would still work so I would replace the Opamp first and if it still doesn't work then I would look elsewhere for the problem .......

Oh ok, the caps seem ok at simple sight. So the IC first it is then.
When I disconnected it after beeing miss-connected I touched one capacitor and it was HOT, but maybe they are ok.

[amptramp]

Do you have access to a meter? If so, lift one side (If that's possible) of the cap to check it.

No I don't 

(psu bypass) caps will generally fail by exploding , but even if the caps failed the circuit would still work so I would replace the Opamp first and if it still doesn't work then I would look elsewhere for the problem .......

Oh ok, the caps seem ok at simple sight. So the IC first it is then.
When I disconnected it after beeing miss-connected I touched one capacitor and it was HOT, but maybe they are ok.

If the capacitor was hot, it was conducting DC current which means it has failed.  It looks like the IC and all the electrolytics need to be replaced.

[R.G.]

Do you have access to a meter? If so, lift one side (If that's possible) of the cap to check it.

No I don't 

This is one of those points where you need to think really, really, really hard about getting a meter of some kind. There's very little you can do in electronics beyond paint by the numbers without a multimeter of some kind. Fortunately, simple meters are available for much less than the cost of parts for another pedal. I don't know your location, but I have seen meters on sale for US$3.00 to $10.00 that would do all the simple stuff you'll need for work like this.

Oh ok, the caps seem ok at simple sight. So the IC first it is then.
When I disconnected it after beeing miss-connected I touched one capacitor and it was HOT, but maybe they are ok.

If a capacitor is hot under power from a low-power supply like a 9V battery, it is dead or dying. Capacitors do not get hot in normal operation, so either something beside them heats them, or they are leaking enough inside to get hot, and this last is a sign of impending death.

Given that, I would replace C5, 6, and 7 and the IC to start with.

[Pancra85]

Wait... I do have a multimeter, I thought armdnrdy was refering to some kind of capacity tester... thing.
But how to test if the capacitor is working with just a multimeter? Or do it needs a capacitor function? Because mine doesn't

Another question, to protect it from inverse polarity, a simple 1N4001 diode in series from 9V to the node above C7 should work, right?

[Mike Burgundy]

Reverse biased bipolars will fail if they haven't already. Semiconductors will probably either fail or suffer from all kinds of degradation, so just replace the IC and C6 and 7 (not expensive enough to bother anyway). C5 is probably ok (the opamp will not be able to churn out -4.5V)

[armdnrdy]

Mike's correct.

With your meter you can only check if the caps are shorted or open. But you can't check if they're "good". There are other ways that a cap can go bad. The capacitance can change and the ESR can go high. As far as measuring the ESR, that takes a different meter entirely.

Take R.G. and Mike's advise. Change the caps, they're cheap!

[Pancra85]

Will do, thanks again!

[Mike Burgundy]

Another question, to protect it from inverse polarity, a simple 1N4001 diode in series from 9V to the node above C7 should work, right?

Yes, that is one way. Its only drawback is that you lose about 0.7V - no biggie. The reverse-diode-to-ground polarity protection that most commercial (such as BOSS) pedals use is rubbish and only protects from *very* short mishaps, such as accidentally touching the battery terminals the wrong way when changing a battery. Wrong adapter polarity  will either have the adapter fry or burn the diode, and then the reversed voltage will still tear through your circuit.
RG has some great stuff on better polarity protection up at GEO (link available in the top left hand corner).