Common when they reach this age. Filters in the DC-Dc converter need replacing. Get it done soon or the transformer windings will short and the converter will blow up and then you are stuck.
If anyone needs a manual for the Geller MP2, see here:
http://the-checkout-tech.com/manuals/cashregisters/Towa_ET-7626_and_MR1_programming_manual.html
Registerman
January 2012