Re: 922 with "tilted" wave form.

Fabio Trevisan
 

Hello Mlynch,
What you describe looks like a "geometry" or Y-AXIS misadjustment.
If I understood correctly what's the equipment you have it's a T922 oscilloscope.
Looking at the Manual that is available on the TekWiki website (here: http://w140.com/tek_921_922.pdf ), the adjustments are Y AXIS, R474 and "GEOMETRY", R473, both are on the CRT & VERTICAL AMPLIFIER diagram, located on the A1 INTERFACE BOARD.
Manual probably describes the correct procedure to adjust both of them, and this is usually done in the very beginning of the calibration procedure, meaning that most of the other calibrations are impacted to some extent by these 2, as they change the shape of what's being shown on the screen.
Steps usually cover the following:
1. First of all, adjust the trace rotation (adjustment accessible from the side of the scope), for a horizontal baseline (just sweep, no vertical signal).
2. Then, using the X-Y mode, apply a signal to the Y channel enough to span about 6 divisions height, leave the X-channel with no signal (set X input to to GND). This will draw a vertical line on screen... Adjust now R474 so that the vertical line, aligned to the central vertical graticule is perfectly vertical.
3. Finally, change the scope back to normal mode, and apply a square wave to one of the vertical channels, that is big enough to span 6 divisions vertically, and set a sweep speed that you see about 20 cycles horizontally accross the screen.
This setup will pretty much "fill" the screen with a square wave, from bottom to top, left to right. Now you can adjust the geometry adjustment (R473) to correct any "Pillow" or cushion distortions of the screen, so that the overall shape of the displayed waveform is all "squared"...
4. The geometry adjustment, if it requires too big re-adjustment, will have some side-effects to the Trace rotation and the Y-axis adjustment... Repeat then Trace rotation and Y-Axis again, to make sure that the screen remains aligned on the horizontal and vertical directions.

All that, above, assuming that - overall - the scope doesn't present other misbehavior... However, the procedures above cannot assure you that everything else is or will remain correct.
Since re-adjusting the Y axis and Geometry may have some impact on the size of the waveforms displayed, by touching those adjustments, be aware that you may need to readjust Vertical Gain and Horizontal gain... and this will require that you have means to adjust those, or accept that they may become "off" by some amount.

Rgrds,
Fabio

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