I have a Protek 20MHz scope that doesn't display the vertical line of a square wave or a sawtooth. Sine and triangle are both fine. I have tried both channels and every possible combination of settings to no avail. Any ideas? Cheers, Dave
Is this a CRT type unit?
If so, the problem is the raise time, it's exceeding the scopes CRT response time, and most likely it's driving circuits. It sounds like you have a high BW input with a Low BW response.
If you have a calibration function for your 10:1 probe, use it to adjust the corners of the square wave, it may ease the response enough for you to see the vertical.
Also, bringing up the brightness should show you a faint vertical line.
P.S. This is common on a CRT scope, your Low Pass filer may help you here if you have one.
Thanks Jamie
Yes, it's a CRT. I was able to get an extremely faint vertical line using the cal output and brightness on full bore. I then breadboarded a filter and am now able to see the lines quite clearly on both square and sawtooth.
Thanks again for your help, I was beginning to think that my new purchase was faulty!
Cheers,
Dave
Jamie wrote:
Why would you want to do this? Your filter degrades the rise times, to the point where the oscilloscope can display them, hence the display you have will be meaningless. What you see is now definitely not what you've got.
In a nutshell, the rise of the signal is faster than the writing speed of the CRT. You have to live with it.
Just "imagine" the vertical portions, and measure rise times between the ends of the opposing horizontal portions, bearing in mind that the rise time of the vertical amplifier will be 17.5 nanoseconds for a 20MHz bandwidth, assuming the usual first-order response.
--
"Electricity is of two kinds, positive and negative. The difference
is, I presume, that one comes a little more expensive, but is more
durable; the other is a cheaper thing, but the moths get into it."
(Stephen Leacock)
I ran the signal through the filter to assure myself that my new $420 purchase can actually display a vertical line. Now that I can see that the display is not faulty, the filter can be removed and I can use the scope "normally". It's my first scope, and I just wanted to make sure that I didn't have to return it under warranty!
Thanks again for your help guys,
Dave
Fred Abse wrote:
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