In 2005, a friend asked me if I could fix his scope. It was this nice Telequipment D83 mainframe scope with a dual trace plugin and delayed time base. This is a real good scope for most electronics work.
The CRT lighted up for a moment and then turned black. I checked the voltages on the CRT base. These were too high and the CRT was cut off, the voltage between grid and cathode being too high. I did some checks in the control circuit and found that one of the 10M resistors in the control loop of the HV generator was interrupted. Replaced it and I was able to get an image.
Then I found that brightness control wasn't working well. Also, blanking on flyback didin't work. Somebody had put an extra resistor in the blanking circuit. I removed that one and had a better picture (forgot to take a new photograph so the picture on top still shows the image without blanking).
Now triggering was very unstable. I noticed the trigger circuit was oscillating round the trigger point. I was able to get the timebase working by setting the hysteresis control. This wasn't very satisfactory, but seemed to help. To be able to make measurements on the time base, I made an extension connector so I could operate the time base outside the mainframe.