Learning to use an oscilloscope and an old floppy drive

Robert,

Your setup is pretty close to correct.  You might need to raise the trigger voltage level up a bit (Yellow triangle on the far right side of the screen). The level is currently set at 11.6 volts (Edge CH1 box near the top of the right side of the screen).  As it sits right now, the trigger is near a glitch in the falling side of the waveform and maybe causing your noisy readings.  Ideally you would like the trigger level to be half between the maximum and minimum points of the waveform, but clear of any strange transitions in the signal.

Good luck,

Gene

Hi Robert,

I fully agree with Gene’s advice so make that adjustment.

The period in yellow at the bottom seems pretty stable.  If you convert the 60.2 kHz frequency in the manual to the period it comes out to be 16.61 microseconds. The display is about 16.67 so pretty close.  This assumes the scope uses “m” for micro instead of “u”.  The scope may be showing frequency as instantaneous, including glitches, and using a different method for determining period.

Frank

You may have used “Auto” to determine the trigger settings.  This is one of those time when manual is needed.

Also, I wonder if that's just a 12V rail, with no activity, because the 'scope says 680mV p-p, and the frequency looks close to mains frequency, if that's 10msec per division (I'm not familiar with Siglent 'scope displays). No idea why f= is in kHz though, might be a configuration issue? I think it might be supply ripple, which might or might not be normal.

The 'scope just displays the voltage as it changes over time, however because you can zoom and level-shift, and end up looking at a magnified portion, it's good to know approximately what waveform you expect to see, so that you have that context to better understand what the 'scope is displaying compared to what it should be displaying.

That is a good point. 

Robert, see if you can display the settings for the time divisions on the screen.

Hi Frank,

I think it's likely just mains ripple, because the 'm' should mean milli - I hope!

I Think you are right!

Hi Robert,

Once you have a feel of where your scope displays the X and Y information, i.e. time in millisec or microsec per division for the X-axis, and Volts or millivolts on the Y-axis, so that you can see if the signals are changing in the approximate time that you expect, and in the approximate voltage levels that you expect, then you'll feel a lot more comfortable with your 'scope (different 'scopes show the information in different places on the screen). Also, no signal is 100% perfect, so you'll see deviations like ripple or other effects, depending on how zoomed-in or how zoomed-out you are, on either the X or Y axis, or both.

The automated measurements are useful when you are happy with what is represented on the screen (and sometimes the measurements rely on precisely what's on the screen rather that what's actually happening on the wire), and the measurements will provide you with the most confidence when you can back it up by also seeing on the screen approximately what you expect to see (or don't expect to see, in error conditions! - that will come with practice).

Ugh..it would help if I read the service manual correctly.  "Use TP2 and 3".  I was on TP4.  When I use TP2 I get this:

I haven't figured out how to make it the time division from peak to peak....aaaggghhh