I'm looking for a schematic or a fix for my Zoom G2 Guitar multi FX. My son plugged it into and 18VDC power supply instead of the required 9VDC. Now it wont turn on. Any Help is appreciated.

Unfortunately, battery jacks and plugs similar to the type you're describing do not have any real standardization - unlike the outlets and plugs in homes and businesses have.

You best bet is to either bring the plug / jack to a shop to match it or contact the instrument's manufacturer to obtain the connector specs for physical dimensions

Be sure to obtain the power requirements in either watts or amps so that you can obtain a power source capable of delivering what you need without overheating during longer periods of use. Adding 25% to 50% more amps or watts to the minimum required should provide years of trouble free service. Example: 9VDC at 50 watts should be supplied by a 9VDC 62 watts or even 75 watts; or in the case of a rating of 9VDC at 6 amps should be supplied by a 9VDC at 7.5 amps or even 9 amps. With DC powered devices, make sure you observe proper polarity! Good luck!

Check plug first the one you plug in wall if there is a small black box at point were you plug in ,there is a transformer in there sometimes they short out .Check with multi meter if it is good then try schematic or Circuit diagram

Download n install 2 softwares for G2 from ZOOM website.
1. USB subsystem. Driver to connect zoom fx to PC/Notebook.
2. EDIT & SHARE. Software to create/copy sound patch.

Connect USB cable from G2 to PC/notebook.
No need adapter power supply, because the power is supply via
USB cable from PC/notebook.
Open EDIT & SHARE. It's easy,like copy,paste,rename,delete etc.
Just open the menu that you want to do and follow the
instructions. Sound patch can be load from files that you
download, or create it in EDIT & SHARE.
Patch can be load one files or group. Right Click the sound that you want to change,copy-paste it from new file/sound.
You can import/export files/patches from/to PC library (downloaded files).
It is recomended that you save/backup your original files,before load new sound.

I hope this helps.
Regards.

This seems to be a battery problem unless you use an AC adapter. If it does it on AC, I would check my guitar cord and power supply. The wrong power supply could do that and a bad guitar cord can as well. If you use a speaker cable as an instrument cable, it could do the same.

The guitar needs to be plugged into it, to turn the unit on. A full manual can be found here for that Zoom model:
https://www.zoom-na.com/sites/default/files/products/downloads/pdfs/E_G1_G1X_3.pdf

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You can find or buy here,in Indonesia:
It's very cheap, about 5000 IDR or it's about half US-$.

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No. You will need to use an amplifier, home stereo, P.A.etc. I would recommend insertion in an effects loop if your amp has one.

Check if it might be an intermittent input or output jack by wiggling these. Jackks are notorious for problems. Often the soldering of the jack to the circuit board seperates causing noise.

I doubt you will find such a thing- altough- Canon web site tech support may have a clue. but you should not need it if you have the skills to make such an item- just make it and stick it where the other came out.