You may find that the key switch is hard soldered to a pwb and in turn that is then connected to the main pwb, if you have not got a problem changing modes on the unit then there may be nothing wrong with the soldering and the switch may be faulty, if this is the case you should talk to you dealer for repair or replacement. If you want to check inside for youself then there should be a screw under the printer cover area and the whole top cover should then lift up, be careful of the power and draw cables as there is not much play in them for service, but these can be un-connected and you can then look at the switch pcb and see if there is a problem.
Simon, April 2006