No. Works for me (Firefox, Win10).

 

No. Works for me (Firefox, Win10).

Am I perhaps posting incorrectly somehow? I only see "edit" just after I do a reply. Even that goes away the next time I refresh.

 

Am I perhaps posting incorrectly somehow? I only see "edit" just after I do a reply. Even that goes away the next time I refresh.

And of course, in accordance with Murphy's Law, just went back to the original post and the functions were there (did nothing different)!

 

Is this perhaps something to do with number of posts?

 

Is this perhaps something to do with number of posts?

The only thing I could see was that it seemed to coincide with when the thread went to a second page. Hard to see how that would make a difference. Regarding the original post, I have been using the scope as much as possible on some other small projects, and the noisiness of the controls is now much reduced. The scope had been sitting idle for quite some time (years). As long as I ignore the extreme edges of the display, it is quite adequate for any measurements I would need. Still trying to free up enough time and gumption to consider cracking the case and poking around. Too many things on the to-do list (not to mention the honey-do list). My thanks to everyone for their valuable input.

 

Can you post photos of the screen so we can see how much the trace droops?
If it is not too bad then you may want to just leave it alone.

 

Can you post photos of the screen so we can see how much the trace droops?
If it is not too bad then you may want to just leave it alone.

I am leaning heavily toward your recommendation. Will look into getting a photo. Neil.

 

I have been using the scope as much as possible on some other small projects, and the noisiness of the controls is now much reduced.

Exercise is good.
Any switch or pot that is noisy will be helped by twiddling it back and forth many times.

 

I am leaning heavily toward your recommendation. Will look into getting a photo. Neil.

OK, here goes my first attempt to attach a file...I put channel 1 at the top to show how flat it can be. Channel 2 closer to the bottom shows the distinct curve at both ends. Both channels behave exactly the same depending on screen position. Ignore the reflection of my wife's fingers, they aren't part of the display!

 

Can you post photos of the screen so we can see how much the trace droops?
If it is not too bad then you may want to just leave it alone.

Photo posted.

 

Thanks for the photo. Nice manicure!

Ok, it doesn't look too bad. I would leave it alone. However I will have a look and the schematic and see what I could find. Of course you will need your other scope to diagnose this if we want to pursue this further.

 

Thanks for the photo. Nice manicure!

Ok, it doesn't look too bad. I would leave it alone. However I will have a look and the schematic and see what I could find. Of course you will need your other scope to diagnose this if we want to pursue this further.

That got a good guffaw from her.
I notice in the schematics that there is an astigmatism adjustment. Could that be a possibility? It seems to be simply a pot connected between a high voltage rail and ground, and the wiper going to one of the CRT's grids.

 

With just a spot displayed (XY mode) or very slow timebase, the astig and focus controls work together to make a nice small spot. If the astig is misadjusted then the horizontal and vertical parts will be focussed at slightly different settings of the focus so you get an oval spot.

 

No. I think astigmatism adjustment affects the oval-to-round shape of the dot on the screeen.

 

No. I think astigmatism adjustment affects the oval-to-round shape of the dot on the screeen.

If the astig is misadjusted then the horizontal and vertical parts will be focussed at slightly different settings of the focus so you get an oval spot.

 

Hello,

This is what circuitstoday says:
Focus Control.

In the electron gun of a CRT, middle anode is kept at lower potential with respect to other two anodes and it acts like an electrostatic lens and focal length of this lens can be varied by varying the potential of the middle anode with respect to other two anodes. So focusing of an electron beam is done by varying the potential of middle anode with the help of a potentiometer, as shown in figure. By increasing the positive potential applied to the focusing anode the electron beam can be narrowed and the spot on the screen can be made a pin point.

Astigmatism.

This is an additional focusing control and is analogous to astigmatism in optical lenses. A beam that is focused at the centre of the screen would be defocused at the edges of the screen because the lengths of the electron paths are different for the centre and the edges. Adjustment of this control gives a sharp focus over the entire screen. This control is affected by varying the potential of deflection plates and accelerating anodes.

https://www.circuitstoday.com/basic-controls-of-a-cro

Bertus

 

On the ones that I adjusted it didn't work like that. Say you display a square wave. The focus control may focus horizontal and vertical sections at a different setting. Adjusting the astig control can then make both parts in good focus.
https://aip.scitation.org/doi/10.1063/1.1746051


[Edit] Incidentally, that's the way the astigmatism in my eyes works too except I don't have a astig pot to twiddle!