Help with Oscilloscope - Missing lines?

[Dave Nubury]

Just picked up a used scope. 20MHz.. - Supposed to be in great working
condition. Came with no leads.
I just attached a couple of aligator clips to the input (Ch1) for now.

It seems to show AC fine. (Nice sine wave)..

However if I try to watch 5volt logic pulses from different sources, the
vertical line in the state changes seems
to be missing. For example. i would expect to see something like:
______ _____ _____
| | | | | |
__| |____| |____| |__

but what I'm seeing is:

_____ _____ _____

_____ _____

Is this normal? Does it have something to do with not having a probe maybe?
Crapy scope?

I would appreciate any info.
Thanks
Dave

 

[CJT]

Dave Nubury wrote:

Just picked up a used scope. 20MHz.. - Supposed to be in great working
condition. Came with no leads.
I just attached a couple of aligator clips to the input (Ch1) for now.

It seems to show AC fine. (Nice sine wave)..

However if I try to watch 5volt logic pulses from different sources, the
vertical line in the state changes seems
to be missing. For example. i would expect to see something like:
______ _____ _____
| | | | | |
__| |____| |____| |__

but what I'm seeing is:

_____ _____ _____

_____ _____

Is this normal? Does it have something to do with not having a probe maybe?
Crapy scope?

I would appreciate any info.
Thanks
Dave


Think about how fast the beam is moving across the screen in the

vertical portion compared with the horizontal portion, and what
that means for its brightness.

--
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form che...@prodigy.net.

 

[Jim Yanik]

"Dave Nubury" <remove_me_david_nugent@hotmail.com> wrote in
news:2JW8e.39108$vt1.25150@edtnps90:

Just picked up a used scope. 20MHz.. - Supposed to be in great
working condition. Came with no leads.
I just attached a couple of aligator clips to the input (Ch1) for now.

It seems to show AC fine. (Nice sine wave)..

However if I try to watch 5volt logic pulses from different sources,
the vertical line in the state changes seems
to be missing. For example. i would expect to see something like:
______ _____ _____
| | | | | |
__| |____| |____| |__

but what I'm seeing is:

_____ _____ _____

_____ _____

Is this normal? Does it have something to do with not having a probe
maybe? Crapy scope?

I would appreciate any info.
Thanks
Dave

The rise time of the input signal is too fast for the CRT phosphor to
visibly display at the chosen sweep speed.The E-beam is moving much faster
in the vertical axis than the horizontal axis,thus less time for the
phosphor to absorb the beam energy,thus the phosphor absorbs much less
energy,with resultant lower light output.If you looked while in a darkened
room,or with an image-intensifier,you might see the rising edges.
Some phosphors are better than others for certain conditions.
Phosphor choice is always a compromise.

--
Jim Yanik
jyanik
at
kua.net