Damaged pedal purchased from eBay and I need a little help troubleshooting

[Belanger]

I'm trying to trouble shoot a pedal I bought used off eBay. When it arrived I opened up the back of it like I always do. Klone circuit FYI  and noticed one of the opamps didn't line up the the notch correctly so I took it out and turned it around in the pedal and powered it on. Now the female dc jack that's mounted to the pcb is getting really hot to the touch right away and that burnt plastic type smell after a few seconds.   I've ordered all new opamps for the pedal is there anything else I need to worry about?  Everything visually looks ok so I'm assuming I don't need to worry about the other bipolar components

[GibsonGM]

You didn't try it out right when you got it to see if it worked?   Did you expect it to work, or did ya buy it "non working" in order to fix it?  Could that opamp have been in the right way, and YOU turned it around the wrong way?

Anyway, from your basic description it sounds like you reversed the opamp and shorted something out.   However - are you sure your DC power supply was connected with the right polarity?  The plug on the supply can often be reversed from what you want...  With no opamp in there - is this when the DC jack "gets hot"? 

If you post a direct link to the schematic and more info re. your DC power supply, we can maybe tell ya what is probably going on.   Maybe post a pic of the board, where that power in jack is, showing whatever components it's surrounded by (protection diode maybe?).

[R.G.]

Was that an opamp or the charge pump IC?

They're in the same 8 pin DIP package, but work very, very differently.   

[Belanger]

No I didn't reverse it and short it out.  The notch in the opamp didn't match the direction of the notch of the socket.Also was meant to be a operating pedal. Also it seems to still work when I turned it on and checked everything out.  After about 5 seconds of being on the dc jack that's mounted to the pcb was so hot to the touch it could practically burn you.   

I'm not sure if the charge pump was ever reversed or not just one of the TL072's

[Belanger]

Also the correct 9v Center negative was used

[Belanger]

I'm not talking about with no op amps in either. I'm talking while everything is properly installed as it's supposed to be. 

[Belanger]

[GibsonGM]

Well, you asked "what you need to worry about"...that much I CAN tell you, Belanger...you need to check that there isn't a short somewhere that is making the DC jack get hot.   

You should check that the opamp is, in fact, in the right orientation - perhaps check the ground pin, be sure it goes to ground, y'know....check your diodes, be sure nothing got toasted there...my feeling is that something IS toasted, evidenced by the pedal drawing so much current the jack is getting hot.  Could be someone messed up the soldering at the jack, or it could be something else...

How does this thing do on battery?

PS your pic just came in after I wrote this....if you fired it up w/opamp reversed, that is likely junk now.

[Belanger]

Before I ever fired it up I opened the back and saw the op amp was reversed.  The stencil on the pcb shows which direction the notch in the opamp socket should go.  The op amp how ever was not lined up properly   The notch of the op amp was on the opposite side as the notch of the socket. After I turned it around I fired it up and it works.  But there's way to much heat for everything to be normal.  And that burning playing smell.   

I'm so sorry to bug ya guys and I really do appreciate the help

[Belanger]

I haven't tried it on battery yet.  I'll do that now

[Belanger]

Ok I did that and only the charge pump is getting hot    So I'm guessing it had to Of been reversed at somepoint as well    So it's safe to say I should replace the opamps charge pump inc and that should be all?

[GibsonGM]

Dude - what if, in the factory, they made an error on the PCB silk screen?  Why would the opamp come from the factory reversed??

- Did you try it out before you took the back off it?  It may "work" now, but not the way it was meant to - something COULD be blown because you reversed that opamp.  The way to check the orientation would've been to find the opamp pinout, maybe look to see if its ground pin was connected directly to gnd, its "+" pin directly to "+" of the battery snap....

If this were mine, <<<after ascertaining that there isn't a short on the power rail (continuity/resistance between + and minus)>>>, I would put a brand new opamp in there, after finding the gnd and power pin to be sure of its orientation.  In fact, I'd sub them all before ever powering on again.  There's a lot of stuff one can do in 5 minutes that would be hard to show a noob...like, test all the diodes, be sure they show about .5V or SO on a diode check (less if they're Ge).   Check the caps with ohmmeter....   

If you don't have a spare, you could build a circuit that takes the opamp - can you do that?  And test that it does work.   If they are the same opamps, I'd try them all.  (What part numbers are they, by the way?)

My money is on that it came functional, and by swapping that opamp, you may have fried it and some if it's friends (associated components).

WITH the opamps in, no DC power plug...what is the resistance reading between + and minus at the battery snap?

   

[R.G.]

"Easter egging" (swapping in parts blindly, hoping to replace the -one-part that was causing all the trouble) is a very expensive way to debug.   

[GibsonGM]

"Easter egging" (swapping in parts blindly, hoping to replace the -one-part that was causing all the trouble) is a very expensive way to debug.   

Me, or him, R.G.?         

We can probably be fairly sure something is shorting, if the DC jack gets hot....so, check your resistance across the battery terminals (with a plug in the input jack!), right?

If it comes back high enough to feel good about there not being a short, then I'd take the 70 cent hit on a TL072 (if that's what it is) back in the spot he took it from, the way it was originally...maybe look at the voltages at the socket pins with no opamps in place first, check all grounds and power connections for 'truth', but man - how do you tell a noob how to proceed other than this?    *shrug*

It could even be a burned trace, if he's unlucky. Or just an opamp...

A schematic would be nice.

[duck_arse]

take the two opamps outta their sockets, and then measure the volts on the socket's supply pins. while the opamps are out, does anything get hot? is there anything mounted under the dc socket, or on the copper side of the board?

[karbomusic]

After I turned it around I fired it up and it works.

Did it work before you turned it around?

I still can't work out in my head why someone would purchase a pedal, not try it out, then 'fix' it. Humans made that pedal and humans make mistakes everywhere, including silk screens, not only that, machines make mistakes too, because they were programmed by humans. So, everything is now up for grabs unless you tested it before _touching anything_.

[Belanger]

It was a used pedal.  Not a new pedal

[Belanger]

The pedal still works so I obviously didn't fry the op amp when I reversed it.  The problem is the charge pump it's the part that's overheating when I use it on battery power and the dc jack and charge pump when it's running on a wall wart. The pedal still sounds like a klone    I've ordered a new charge pump for it I'll let ya k ow what happens from there.   Please feel free to share useful Info

[karbomusic]

I never once said it came from the factory.  It was a used pedal dude

It didn't build itself so factory just means someone other than you in this case. Let us know how it goes.

[Govmnt_Lacky]

18 posts in and no one has referred to the Debugging page? Say it ain't so....