Yesterday my granddaughter Victoria and I used my oscilloscope whilst I was teaching her some basic electronics. Later in the day this oscilloscope started to misbehave and appeared to have an intermittent fault, so I decided to leave it turned on all night in the hope that the fault would become permanent, making it easier to find. This morning when I got up the oscilloscope no longer worked, so after doing one or two other jobs I decided to endeavour to fix the fault. This was not as easy as it might have been since I have never managed to obtain a circuit diagram for this instrument, however I have a reasonable idea of its interior layout and general functioning. Having checked that most of the voltage supplies were there, and the EHT was on the tube, it was fairly easy to see that the tube had been biased very hard negative, so that no current flowed. The bias fault was found and the oscilloscope returned to working order, however, I will need to take it apart again in order to reset the bias level as I now have insufficient control of the intensity.
Having spent several hours on this, I thought it might make a blip as I could not think of anything else.