Oscilloscope - square wave verticals not visible (noob Q)?

[cfcubed]

Picked up an older 20Mhz scope cheap and afraid I might have gotten what I paid for.. Or maybe I don't know what I'm doing

No matter how I try to adjust things the vertical portions of the internal cal sq wave never show (see below). The 1khz sq tab cal on the front is supposed to produce a nice square wave but it doesn't look that way to me...



A/C waveform from an adapter looks ok to me:


I searched this forum but didn't see any pics or problems like this one...

Any thoughts would be much appreciated!

[Conrad Hoffman]

The internal calibrator is fairly low in frequency. The edges are fast compared to the frequency, so you shouldn't see them. If you could see them, it would indicate a problem ;-)

[AndrewT]

Hi,
fast edges hardly show on any scope.
If you turn up the brightness, you might be able to see the near vertical edge, but don't leave it there too long. The bright parts of the trace will not do your screen any good.
If you turn up the frequency of your test sine wave, you will notice a slight darkening of the trace. At the scope's limit the trace can be quite dim and a darkened room will help viewing, or turn up the brightness.

[cfcubed]

Originally posted by Conrad Hoffman
The internal calibrator is fairly low in frequency. The edges are fast compared to the frequency, so you shouldn't see them. If you could see them, it would indicate a problem ;-)

Thanks for the quick reply!

I was hoping it might be the internal 1Khz cal. generator itself...
But the user manual drawings of the test & the other scope pics I see of sq waves have vertical lines (e.g. at least faint ones).

Maybe if I can get ahold of (or build) a sine/square generator I could use frequencies that would show full square waves....

Glad to hear it might be me & not the scope

[bigwill]

There is nothing wrong at all with the generator and scope

[jackinnj]

There's probably a little adjustable capacitor on the scope probe -- you can adjust to this to square up the traces. On my Tektronix 2465 the adjustment is on the connector which mates to the scope, on an old Pomona the capacitor is on the probe itself. Don't get carried away twiddling with it, only a couple degrees turn are necessary. Through the seasons you have to adjust ...

[cfcubed]

Thanks everyone for all the info... Guess there's nothing wrong here, I was able to make the observations AndrewT talked about & see that the probe adj can fine-tune the square wave...