I wonder if just the display is going blank or if the controller is actually cutting out due to a loss of power...
When it's in the failed state, can you program it?
Does it beep when you press a button in the failed state?
When the clock is set, then the display goes out, when it comes back, do you have to reset the clock?
Can you can and post the schematic page if the "mini-manial" in the unit?
If it's your board, that can be repaired