Telequipment D83 oscilloscope

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.

There was still room for improvement, but my friend was happy with the scope and wanted it back badly. So maybe I'll finish the job later.