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Pretty much what the title says.

Later I tried a 9V adapter which I brought from home and the pedal isn't releasing any sound. On/off lights are saying it's off.

Cables and the 9V adapter from home shouldn't be the cause (tried them with another pedal and that worked).

The problem definitely lies within the pedal I lent the friend.

Also, I have no idea about electricity-related stuff. Just thought I might mention that.

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What is the voltage of each adapter? Are they both AC or both DC, or are they different? –  Kevin Vermeer Aug 30 '11 at 22:09
    
The 7V one is AC and the 9V one is AC/DC. Also the 9V one has switches for changing the polarity and voltage from 1.5V to 12V. Would you prefer a picture over this description? –  Derpie Aug 31 '11 at 8:51
    
Sure, pics of the adapter labels would be great. The 1.5V to 12V switch is particularly confusing to me. –  Kevin Vermeer Aug 31 '11 at 9:30
    
I noticed something while taking the pictures: on the one which I thought was 7V wasn't written 7V but 12V. I misread '7W' for '7V'. I realize I screwed up badly here with the descriptions and I'm sorry about that. What are the possible scenarios now? Also, here are the pictures: the 1.5-12V one - i.imgur.com/gQDMO.jpg and the 12V one - i.imgur.com/QKLr0.jpg . Once again sorry. –  Derpie Aug 31 '11 at 12:23
    
Judging from the pictures and your other comments, the polarity was wrong. So, if the Pedal is well built, most probably only a fuse is burned (would happen in a system with a parallel reverse polarity protection with a fuse). If there is no fuse then most probably the power input stage is burned out. You'll have to post some pictures of the PCB inside your pedal for further information. –  Masta79 Aug 31 '11 at 13:51

4 Answers 4

up vote 5 down vote accepted

Worst case:

  • The voltage and/or polarity of the power adapter was wrong. This could have caused damage to the pedal.

Medium case:

  • The pedal drew too much power out of the power adapter and blew the adapter.

Best case:

  • Nothing happened and it's all fine.

Check the voltage and polarity :

This is the symbol for the DC voltage:

(A line with 3 dashes under it)

This is the symbol for the polarity:

Polarity

The dot in the middle represents the hole in the center of the power plug. The C shaped part is the main body of the plug. Make sure this matches what the original power adapter had.

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Thank you for this answer too, the polarity seems to be negative (that open circle-thing is pointing with the opening towards the (-) sign) and the voltage seems to be 9V and there's "IN" written after the line-with-3-dashes-under-it. It matches the adapter I have at home and doesn't match the adapter my friend gave me back (which I'm pretty sure isn't the one I gave him, because of the shape). Maybe the pedal itself just got stomped to death by the friend. –  Derpie Aug 30 '11 at 17:54

If the pedal is defective it won't be due to the adapter's power rating. Check if the voltages on both adapters are the same, and if their polarity is the same as well. Also check if it isn't AC where it should be DC.
For everyday's purposes 7W and 9W are pretty much the same. The pedal won't require 9W, so the 9W device will have some headroom, which the 7W device won't have, but it won't cause any trouble. If it would, it would be the adapter which would fail, not the pedal.

edit
From the pictures you linked to in your comment (this and this one) it appears that they have reversed polarity and a different voltage. This could be bad: this kind of devices is usually not well (or not at all) protected against reverse voltages; they simply rely on you using the supplied mains adapter. Final.
How big the damage is depends on what's inside, but digital (like \$\mu C\$ or common logic) or analog (like opamps) ICs are probably gone. See if you can post a picture of the internals, so that we can assess how big the damage may be.

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Thanks for the answer sir. Maybe the pedal IS defective. It can be also powered by a battery like this: en.wikipedia.org/wiki/Nine-volt_battery so I'll try that and will give an update (sorry that I didn't think of that first). –  Derpie Aug 30 '11 at 17:47

Unless you have an exotic piece of technology, schematics for the pedal should be easy to find with a bit of time on google. find it/post it here, and figuring out what could have fried should be straightforward.

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There is one potential problem that I don't think has been brought up.

The difference between and unregulated and regulated adapter. The adjustable one is "stabilised", which I interpret to mean regulated. That means that when under any load, up to its maximum, it will keep the regulated voltage within a certain percentage.

The other 12V adapter is not regulated - who knows what output voltage it could give out? An unregulated adapter can give up to 50% more at light load; I'd imagine that the pedal doesn't draw that much current. That means it could have been fed 18V.

I don't understand the internal workings on an effect pedal, but I'd imagine it would be easy to repair. It's likely one or two op-amps are fried, or a cap has blown from the increased voltage, but the damage is likely to be obvious.

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