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Oscilloscope question: no tracer, instead a sedintary Square?

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Logrhythm

New Member
Hello everyone,

My oscilloscope turns on but in place of a tracer moving from left to right there is a solid square that comes out in its place. The square is able to be moved about with the vertical and horizontal knobs but thats about it. Any help as to how to get the tracer going would be greatly appreciated. The Oscilloscope is a HP AN/USM-281A.
Thank you


- Miguel
 

Dean Huster

Well-Known Member
First off, Miguel, that's "trace", not "tracer". The USM-281A was the Hewlett-Packard version of that series; Fairchild, Tektronix and DuMont made the 281B, C and D respectively as I recall -- well, I'm abolutely positive the C was Tek's. Anyhow, that's just a little trivia.

You have two plug-ins in this scope, a vertical preamp and the timebase. Make sure that the timebase trigger mode is in the "AUTO" vs. "NORMAL" or "SINGLE SWEEP" mode and that the TIME/DIV is set to around 1ms/DIV. On the vertical preamp plug-in, simply set it for CHANNEL 1 only with the input coupling switches set to GND.

With this, you should have a solid horizontal sweep which you can move a little left and right with the horizontal position control (on the timebase) and vertically with the vertical position control (on the preamp).

Let's see where you are are now.

Dean
 

Logrhythm

New Member
re:

"Trace" not "Tracer", got it. Thanks Dean.

I had one question, when you said "On the vertical preamp plug-in, simply set it for CHANNEL 1...." Where is this exactly?
I set the input coupling switches to GND.
 

Boncuk

New Member
Why not post a picture of your scope so we can see the controls?
 

Logrhythm

New Member
Ok guys,

I tried those things and nothing. All i get is that square like it shows in the picture. The square can be moved around but no trace comes out moving from side to side. Any other ideas?
 

Dean Huster

Well-Known Member
Miguel, turn the intensity down until you can barely see the "trace" and then use the focus control to refine it to a tiny dot. Can you? You may be plagued with power supplies with nasty ripple and the scope will be in need of major repair.

Also, what is written around the knob skirt of the knob located above and between the two attenuator knobs. I think its the vertical function knob. Does it have things like "A", "B", "A-B", "A+B", "ALT", "CHOP" and such?

Dean
 
Last edited:

aljamri

Member
If your CRT vertical and horizontal scan is O.K., This square may resulted if you added X and Y.
 

Logrhythm

New Member
Hello everybody,

I have tried every possible configuration I can think of with the knobs to no avail. I still get only a square in place of a trace. Dean, the focus control does nothing to the square. The intensity knob fades it in and out. Also, the knob skirt does have "A", "B", "A-B", "A+B", "ALT", "CHOP" and such on the knob located above and between the two attenuator knobs. All the selections but one move the square up and down on the vertical axis to a single location. The "chop" option on that knob splits the square into two squares. Any ideas? Thank you
 
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