Michael W. Lynch
The symptom is when displaying square wave (off the front panel), the height of the square wave varies wildly as the trace is moved up and down using the Ch1 or Ch2 vertical shift control. When moved to the bottom the height is around >2.5 squares, when moved to the top the height is around 4 squares.John,
I do not know if this is relevant, but I have a 485 that did a similar thing. The square wave supplied by the calibrator was fine when the trace was centered and as you moved the trace away from center, the trace shrank vertically, to about 10-20% of its original amplitude. This 485 scope had been in storage for a very long time and I traced the problem to a very dirty beam finder switch. I used DEOXIT, IPA and a lot of exercise to clean that switch and the scope returned to normal and signals now display correctly, regardless of vertical position.