oscilloscope help

[johnnm]

I have a Tektronix 475A. It's in working condition (bought it calibrated). When there's no signal being applied to either input, there is no trace. I'm certain that earlier I had a flat line trace when no signal is applied, but now the trace just disappears. For example, when the source is an amp's speaker outputs, you get the wiggly lines you expect, except every second or so, for a very brief moment, the trace disappears. ("Signal" light signifiying a signal is being applied also turns off.)

Any idea on a setting I might have changed or anything else to look for in order to get the scope to display a straight trace line when no signal is being applied? It's irritating.

 

[johnnm]

Well well. After typing that, I go back to look at it and it's working like it's supposed to...*sigh*. Vintage equipment.

 

[Tom Bavis]

That's how it will work in "normal" trigger - trace only when the signal crosses the trigger level. In "auto" trigger you'll have a trace (maybe dim with no signal) all the time though it may disappear briefly when a signal is removed.

 

[hwirt]

Try switching the trigger source to Line

 

[Blue Shadow]

Some Tektronix manuals show the setup procedure for the scope and the results one should get, the dot, the moving dot, the line, etc. This is a good place to start for those that don't know exactly where to set all the dials, switches, buttons and knobs when a scope is missing the trace. It was the only way I could duplicate the trace I saw when I purchased the scope.

 

[Findm-Keepm]

Straight from Tektronix...

From their "XYZs of Oscilloscopes" - available on the web in PDF:

Trigger Modes
The trigger mode determines whether or not the oscilloscope draws a
waveform based on a signal condition. Common trigger modes include
normal and auto.
In normal mode the oscilloscope only sweeps if the input signal reaches
the set trigger point; otherwise (on an analog oscilloscope) the screen is
blank or (on a digital oscilloscope) frozen on the last acquired waveform.
Normal mode can be disorienting since you may not see the signal at first
if the level control is not adjusted correctly.
Auto mode causes the oscilloscope to sweep, even without a trigger.
If no signal is present, a timer in the oscilloscope triggers the sweep.
This ensures that the display will not disappear if the signal does not
cause a trigger.
In practice, you will probably use both modes: normal mode because it lets
you see just the signal of interest, even when triggers occur at a slow rate,
and auto mode because it requires less adjustment.
Many oscilloscopes also include special modes for single sweeps,
triggering on video signals, or automatically setting the trigger level.

Cheers,

 

[donberry]

I have a Tek 462 I believe, I was having problems with my trace and it was all of the switches need a good cleaning - I am guessing mine sat unused for probably a decade or more - easy to oxidize the switches when it is never used