Hi Roger,
I'm sorry to hear about your beloved KN7000
Some of my thoughts....
The fact that you can clear the problem by switching off for a while, would suggest that it is an overheating problem. There is a cooling fan inside the instrument, which may have siezed up or become faulty. To determine if it is operating, you will need to be in a very quiet environment to hear it running. I can hear the fans running in my KN7000s.....
After the instrument has been switched off - say overnight - and you switch it on again, does it then take around the 90 minutes before the fault appears again?
When the fault appears, place your hand on the top of the fixed case, about 18 inches from the left end. Is it quite hot? The power supply is located in this area...... If either of the above two conditions are true, it would tend to confirm an overheating problem.
There have been several reports of one of the voltage regulators in the power supply failing, however, this would normally result in total non-operation rather than a fault which can be cleared by switching off for a short period.
KN7000s do appear fairly regularly on eBay and another good source worth contacting, is
www.whitleybayorgans.co.uk Although they are located in the North East of England, they do send out via couriers.
As far as repairers are concerned, there is one located in Essex -
www.wdgreenhill.com/ They're not exactly in the Gloucester area but they may be able to help.