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First time oscilloscope help

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cihs

New Member
Hi,

I recently acquired a very used BK Precision 1590A oscilloscope. It's the first scope I've owned so I'm completely uneducated at this point. I'm lacking a manual for it, which doesn't help much.

The first thing I'm attempting is to calibrate using the test pin on the front of the unit. Through much Internet searching, I believe (but could be wrong) that I've got the settings correct for the calibration. However, instead of a square wave, I'm only seeing the tops and bottoms of the squares on the CRT. i.e. no vertical lines. Aside from the missing vertical lines, the wave appears sharp and steady.

Given my complete lack of knowledge, I'm hoping someone may be able to:

1. Point me in the direction of a place where I can download the manual
or
2. Barring a manual, provide me with any advice about next steps?

At this point, I don't even know enough to know if the scope is broken or if I'm just doing something wrong.

Thanks!
 

JLNY

Active Member
My guess is that the edges are sharp enough that the vertical lines in between the top and bottom bars are just moving too fast to excite the phosphors on the screen. Are you able to see them, even dimly, if you turn up the bightness? Depending on the condition, you may also want to adjust the focus and maybe the astigmatism to ensure that you are getting a nice sharp trace. It doesn't sound like the scope is damaged, and it should be working more or less correctly if you are getting a trace on the screen.
 

cihs

New Member
My guess is that the edges are sharp enough that the vertical lines in between the top and bottom bars are just moving too fast to excite the phosphors on the screen. Are you able to see them, even dimly, if you turn up the bightness? Depending on the condition, you may also want to adjust the focus and maybe the astigmatism to ensure that you are getting a nice sharp trace. It doesn't sound like the scope is damaged, and it should be working more or less correctly if you are getting a trace on the screen.
Hi JLNY,

Many thanks for your response. I uploaded a video showing the result of adjusting brightness and focus. Still no vertical lines visible. You can see it here:

I tend to agree that the scope is probably okay and I'm doing something dumb. Without a manual I'm somewhat flying blind here, though :(
 

JimB

Super Moderator
Most Helpful Member
cihs,
what you are showing in that video is quite normal for an analogue scope with a crt which is displaying a slow square wave.

If you speed up the timebase, so that you are only displaying one cycle of the calibrator, you may see the rising edge displayed.
Of course if you switch to a very fast sweep, you will see just the rising edge of the calibration waveform.

JimB
 

cihs

New Member
cihs,
what you are showing in that video is quite normal for an analogue scope with a crt which is displaying a slow square wave.

If you speed up the timebase, so that you are only displaying one cycle of the calibrator, you may see the rising edge displayed.
Of course if you switch to a very fast sweep, you will see just the rising edge of the calibration waveform.

JimB
Given this feedback, I attempted to look at something that wasn't square and the first thing available to me was an MOS6502 CPU so I decided to check its clock signal. Here's an image of that: https://photos.app.goo.gl/NyG7uZEbmmCMjSVT8

Clearly, the scope will display vertical lines. I don't know yet how to determine if the frequency is correct, but I think you have me on the correct path now. Thank you, JimB!
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Clearly, the scope will display vertical lines. I don't know yet how to determine if the frequency is correct, but I think you have me on the correct path now. Thank you, JimB!
You're missing the point, that's NOT a square wave, and even if it was the rise and fall times are what's important - a 'good' square wave will have rise and fall times too fast to display, where a 'poor' square wave may be slow enough to see the vertical lines, even if somewhat dimmer. There's nothing wrong with your scope as far as that goes.
 

cihs

New Member
You're missing the point, that's NOT a square wave, and even if it was the rise and fall times are what's important - a 'good' square wave will have rise and fall times too fast to display, where a 'poor' square wave may be slow enough to see the vertical lines, even if somewhat dimmer. There's nothing wrong with your scope as far as that goes.
Hi Nigel. Apologies, but I am missing the point. Everything I read before said that my scope would generate a square wave on the test pin. When you say "that's NOT a square wave", what should my scope be generating on the test pin?

From your second sentence, I'm gathering that if my scope does generate a square wave on the test pin, if it's a 'good' square wave I should not be able to see vertical lines. That's the part I did not know. At any rate, thanks for trying to help educate me. I began by saying I've never used an oscilloscope before. I came here to learn.
 

Nigel Goodwin

Super Moderator
Most Helpful Member
Hi Nigel. Apologies, but I am missing the point. Everything I read before said that my scope would generate a square wave on the test pin. When you say "that's NOT a square wave", what should my scope be generating on the test pin?
Sorry if I confused you, I was referring to the image from post #8 (which I quoted from), which isn't a square wave - hence the sides are easily visible.

The better the square wave the faster the rise and fall times, and the more likely you are not to see them.
 

cihs

New Member
Sorry if I confused you, I was referring to the image from post #8 (which I quoted from), which isn't a square wave - hence the sides are easily visible.

The better the square wave the faster the rise and fall times, and the more likely you are not to see them.
Ahhh, yes. Indeed, I chose the clock pulse because it wasn't square. You have provided me with very good information. From everything I've probed so far, it appears that my scope is working properly. I just didn't have the knowledge I needed before to know that the squares were supposed to look like that. Much appreciate all the helpful replies to this thread.
 

JimB

Super Moderator
Most Helpful Member
To expand a bit on my earlier post, I dug out my old Telequipment D75 'scope, and displayed the calibrator waveform:

Telequipment D75.JPG


Looking closely at the display:
Waveform.JPG


The rising edges of the waveform can be seen quite clearly as a continuous line.
The falling edge is mostly absent because it is moving too fast for the phosphor on the CRT face to respond. If you look very carefully where the waveform starts to fall (top centre of the screen), the falling edge can be seen quite faintly.
If viewed in a dark room or through a viewing hood (who remembers those things?), it is possible that it may be clearly seen.

Note that this probe is not correctly compensated on this oscilloscope, as a result, the horizontal lines are not horizontal.

JimB
 

cowboybob

Well-Known Member
Most Helpful Member
Thank you. I had found that, and about two dozen other scam/malware links that didn't work in prior searches. Were you actually able to download the manual from that link?
Didn't try, honestly.

How about the BKprecision Support Site?

They do want a bit of info from you, but you'd think that site would "act nice" and eventually give you, at the least, a user manual.

Also note that most User Manuals are free, but Service Manuals frequently are not.
 

cihs

New Member
Didn't try, honestly.

How about the BKprecision Support Site?

They do want a bit of info from you, but you'd think that site would "act nice" and eventually give you, at the least, a user manual.

Also note that most User Manuals are free, but Service Manuals frequently are not.
I did send BK Precision a message using their support site basically begging for a copy of the user manual. No word back yet. They have most of their user manuals online, but the 1590a is old enough to not be there. Possibly released prior to the invention of the pdf file format :)
 

JimB

Super Moderator
Most Helpful Member
Note that this probe is not correctly compensated on this oscilloscope,
I was just about to complain about that :D
I thought that someone would pick up on that, which is why I mentioned it.

The D75 is not in daily use and only comes out to play when the fancy digital scope just cannot cut the custard.
As a result the probes are compensated to my Agilent digital scope.

JimB
 

crutschow

Well-Known Member
Most Helpful Member
The falling edge is mostly absent because it is moving too fast for the phosphor on the CRT face to respond.
The phosphor is responding fine, it's just that density of the electrons hitting the screen during the rise and fall time of a square-wave is far less than during the horizontal portion of the wave.
 

cowboybob

Well-Known Member
Most Helpful Member
I found and downloaded a "Parts & Schematics" pdf doc, but, (of course) it's useless as an owner's manual.

(Edited out a site URL since the site was not reliable.)

Looks like your best bet to ask this (or another) forum for help when you need it. Scopes are scopes: for the beginner user, there's not a lot difference between their controls and how to adjust and use them.

Never have a seen a manual so difficult (durn near impossible) to get....:banghead:
 
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