the trick it to get the switch cleaner and or alcohol in to the switch its self and not just spray over it.  To do this you will need to open up the monpoly and remove the curcuit boards.  A hassle I know.  Although you may be able to get to the switch if you have a spray can with a long nossle as you get with some of them.  I can see on mine that you can gett under the yellow switch cap and to the switch it self by passing the nozzle between the PCBs.  You can lso see from here where to 2 wires are solderd to the pins of the switch and you may be able to see if on or more have come loose.  if you still have no joy you may have to remove the PCBs in order to inspect them better.If you not happy with doing this then best send it to a service center if you have that cash to do so.

--- On Fri, 11/7/08, Brinkmann Music <adam@...> wrote:

From: Brinkmann Music <adam@...>
Subject: Re: [korg_mono-poly] problem with "Effects On/Off"-button
To: korg_mono-poly@yahoogroups.com
Date: Friday, 11 July, 2008, 12:30 AM

Mine still lights, but is difficult to turn on and off- takes several tries.  I sprayed contact cleaner on the switch, but it still acts up.   It's the only switch that gives me grief.   I'm sure others will have more constructive help.

On Jul 10, 2008, at 5:12 PM, lang_hat wrote:

Hey MP4-users.
Suddenly the "Effects on/off", on my MP4, has stopped working. The LED doesn't light and  
the effects are not being activated. Its pretty annoying, since I love the effects. Its also very  
weird - it just happened! And There hasn't been any troubles with it before. Any Ideas what  
to do