I have a Potterton timer and occasionally this 'flutters'. It is not in an instruction manual but if you bridge all five buttons, which you use to set the clock and timers, this resets the device.
I had my exchanger replaced in 2003 after 9 years of use. I wonder if I had imput some inhibitor it would have lasted a bit longer. I don't think that you should try running it without the front panel - but then I'm not a engineer.