Oscilloscope trace isn't always even.

[ChristianCMcKay]

So I got this old BK Precision 1541 almost a year ago and it works great except for one little thing that I'd like to get fixed. If I move it, a lot of the time when I turn it on, the trace (with no input signal), will be uneven. It still functions for checking signals, but they're uneven too. If I let it sit for a while, it eventually seems to get a little better.

I've looked everywhere, and can't seem to find anyone else who has this problem. Can anyone help me?

 

[alec_t]

What do you mean by 'uneven'? Is this vertical ripple on the trace? Or non-linearity of the time-base? Is the 'uneven'ness random or regular? If regular, what is the approximate frequency?

 

[ChristianCMcKay]

The best way that I can describe it that is looks like the CRT has shifted behind the graph, except it hasn't. It's still mounted in place like it's supposed to be.

 

[alec_t]

looks like the CRT has shifted behind the graph, except it hasn't

Mmmm, can't fathom that. Vertical, horizontal, focus or rotational shift? Can you post a pic?

 

[ChristianCMcKay]

Mmmm, can't fathom that. Vertical, horizontal, focus or rotational shift? Can you post a pic?

Yeah, I have to wait until it happens again, though. It's working alright for right now.

 

[ChristianCMcKay]

Got an idea to draw out about what I'm talking about.

**broken link removed**

I can move the trace up and down, The volts/division adjustment works perfectly fine too, it's just uneven. The drawing above is just an example of what it's like with no input signal.

 

[PatM]

Got an idea to draw out about what I'm talking about.

**broken link removed**

I can move the trace up and down, The volts/division adjustment works perfectly fine too, it's just uneven. The drawing above is just an example of what it's like with no input signal.

In the upper left panel where the knobs are is a area marked CRT
Between the Intensity and Focus knobs is a small hole with a adjustment screw.
This is marked "Trace Rotation"
Using a small screwdriver, you can level the trace by adjusting this small screw.
Try exercising this screw - maybe the control is intermittant and needs a little action to clean the pot

 

[ChristianCMcKay]

In the upper left panel where the knobs are is a area marked CRT
Between the Intensity and Focus knobs is a small hole with a adjustment screw.
This is marked "Trace Rotation"
Using a small screwdriver, you can level the trace by adjusting this small screw.
Try exercising this screw - maybe the control is intermittant and needs a little action to clean the pot

Wow, that was exactly it. Guess I just completely overlooked this adjustment. Thank you so much!

 

[alec_t]

Ah, so it was a rotational shift. Glad you got it fixed. I had a similar shift with my old scope, but didn't have the luxury of an adjustment screw. I had to unclamp the CRT tube and rotate it physically a degree or so.

 

[ChristianCMcKay]

Yep, rotational. I couldn't think of the word, so I figured I could draw something better than I was thinking of. As for grabbing a CRT, that just doesn't do for me. They're by far my least favorite electronic to work on.

 

[bountyhunter]

The first scope I had was adjusted slightly differently: you loosen the clamp nuts on the CRT and rotate it by hand until it was level......