On Thu, Jul 22, 2021 at 03:02 PM, Grayson Evans wrote:
My 2465B has been sitting on the shelf for a few months. I notice when I
fired it up today that the horizontal sweep is slow, by that I mean that the
calibrator square wave does not line up with the screen scale lines. It sweep
starts out on the left correct but by the time it reaches the right side, it
is off about 1/2 cm.
I checked the calibrator output on another scope and it is correct. The Delta
T measurement shows that the calibrator timing is correct, but it just doesn't
line up with the screen scale. Same for B sweep.
Could this be a screwdriver/pot adjustment (too good to be true Im sure), or
some software calibration? I have maint manual which seems to reference R860
for horizontal gain, but discusses a CAL 01 procedure in detail, more detail
than I can follow.
Any one else have this problem?
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There are good suggestions in the other posts too. Given that delta-T measurement has the same wrong horizontal scale factor, horizontal gain could be an issue as you suspected, although it is strange that the gain is off by ~ 5% (0.5cm error in ~ 10cm).
One more test to check horizontal gain is to apply a signal, e.g. 1kHz sine wave, with 8 division amplitude to channel 1. Then switch to X-Y mode with nothing connected to Ch2, and with only Ch2 selected in the mode switches. Do you see a 8 division horizontal line, or is it compressed too? If you now turn on Ch1, do you see a 45 degree diagonal line? I did this experiment on my 2467B (almost same as 2465B).
You can also use the calibrator output as signal generator, then you will see two dots in X-Y mode. You will need to adjust Ch1 volts/div for 8 divisions amplitude or best measurement accuracy.
Looking at the schematic there is some interaction between x10 gain and x1 gain pots, if you see the gain off in x10 mode it could still be R860.
If you touch R860 you may want to mark the original position in case it is something else. Again 5% error all of a sudden is strange.
Ozan
