Re: 468 sweep offset issue


Jim Popwell <jpopwell@...>
 

Hi,

since you are saying one is ok and this one is out a little…..check all all the settings of every knob on the timebase side and compare knob to knob…...….both a and b and start/end and hold off to make sure you are seeing what you think….

jim

On Feb 24, 2016, at 3:53 PM, analogaddict013@... [TekScopes] <TekScopes@...> wrote:

I am not sure what you mean by voltage offset. With no sweep, there
is always a voltage offset because the blanked beam is located at the
left side of the CRT.
Is the bow on the right 1/4 of the CRT visible in your photos?
It is only slightly visible in the close up photo. It is most noticeable when I have the scope set up per the calibration procedure for Y axis and Geometry adjustment. I will upload a photo of the display symptoms shortly.

According to the schematic for the horizontal amp, when the scope is set up in XY mode (as per the voltage measurement conditions) both plates should measure close to 52V. My 110V rail is 2V high, so it should measure 54V, but either way they should both be the same with the dot centered. Left plate measures 56.7V and Right plate measures 54.3V.
The horizontal position control is off-center to the right side of the display by approx 2 divisions.
Also, when I center the trace in a normal timebase setting and then switch it into XY, the dot is positioned that same 2 division to right offset.

Are you referring to the start point of the A and B sweeps not being
exactly aligned?
The alignment depends on circuit tolerances and there may be no
adjustment for it. At high sweep speeds, it is normal for the start
of the sweep to creep to the right somewhat.
I can probably suggest where it can be trimmed out if we determine
that there is no actual fault.
Yes, I am referring to the A and B sweeps not being aligned. My other 468 doesn't have this problem at any timebase settings. (That one needs more work than the one being discussed.)

What really bothers me about it, and also has me slightly confused, is how to properly adjust the sweep start and sweep cal settings when taking this problem into account.

As per the horizontal cal procedure (it's the first step in this section):
-Set timebase A to 1ms and B to 5us
-Set delay time to 1.00
-Input 1ms time markers
-Adjust so the pulse displayed on B sweep starts at the beginning of the sweep & start of 2nd time marker from A sweep display**

The pulse on B sweep is not displayed if I set it to where I believe it should be - which is coinciding with the start of A sweep (which is the first time marker)
If I don't have it set exactly there, won't B sweep end up being out of tolerance?

I suppose I'll have to go through the waveforms again now that I have a digital scope and see if everything syncs up with the sync pulse, A and/or B sweep start, and blanking/unblanking. When I had checked them with my 465, everything appeared to be correct. Some waveforms just had minor differences in their voltage levels when compared against the manual spec, but seemed OK when compared against the other 468.

I definitely want to fix this and get them aligned. I guess I'm a bit OCD...

I just have a couple things to do and then I can get another picture or two uploaded, then do some waveform checking.





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