Korg Mono/Poly

Hello Sophie

> Is replacing the internal transformer a difficult but documented operation ?
It is the opposite ;-)  it is an easy but undocumented operation - for a 
knowledge person

The schematics are available here
http://fa.utfs.org/diy/korg_monopoly/
or here
http://monopoly.highspies.com/manuals.html

If this information is not enough for you, then ask someone who is able 
to use this information. In UK I can recommend Tony Allgood from 
Oakleysound.
But any other repair shop for electric musical instruments (or radio and 
TV electronics) will be able to do this. But it will be more expensive 
than a stepdown transformer.

Example for Stepdown transformer see
http://www.amazon.co.uk/Step-Down-Voltage-Convertor-240V/dp/B000H9HU5C/ref=sr_1_2?ie=UTF8&s=electronics&qid=1238619815&sr=8-2


Regards, Florian