Learning to use an oscilloscope and an old floppy drive

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.

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.

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

Look up the section in the manual on using cursors

Ohhh, thank you. (Reading PDF manuals onscreen are a PITA btw ) I don't understand why frequency is showing in Hz and manual says it should be kHz?..

Hi Robert,

As mentioned, you shouldn't be looking at the automated measurements such as Frequency, until you're comfortable with what you're looking at visually, the oscilloscope trace. And you need to get comfortable with the X and Y axes.

Take a look at your screen:

The red highlighted bits indicate 2 milliseconds per division on the X-axis, and 10V per division on the Y axis. I've drawn a green box to show you one division, since they are faint lines on the screen.

Now, you can look at the trace and do your own maths calculation for frequency. You can manually count how many divisions on the X-axis to go from one peak of the sinewave to the next. It's about 8 divisions.

At 2 milliseconds per division, that means the period of the sinewave is about 16 milliseconds, which is 0.016 seconds.

Now calculate the reciprocal of that (1/x) and you get 1 divided by 0.016 seconds which is 62.5 Hz. That's almost identical to what the automated frequency measurement at the top-right of your screen is indicating. So, in summary, without even looking at the automated frequency measurement, you can see for yourself that the signal is of approximately 60Hz simply by looking at the trace and counting squares on the X-axis, and doing a calculation with a calculator.

I think you're going the wrong way about it if you expect the measurements to automatically indicate things. You need to first get the trace displayed as you expect. Then the automated measurement will be useful, because the measurement on it's own provides zero context. You have to look at the trace and see that it is what you expect to see, to get the context.

Your signal is a 60 Hz sinewave. There is no reason for the 'scope to display it's frequency in kHz, because although you may have expected 60kHz or something else, that's not what is connected to the 'scope.

Also, by looking at the Y-axis, you can see that the sinewave has a peak-to-peak span of about three squares, or 30V. That also agrees with the automated measurement. I'd conclude that you're looking at the output from an AC mains transformer perhaps, in a country with 60Hz mains frequency.

There should be online video training on how to use oscilloscopes, and the manual should be read too. Otherwise, there can be a risk of damaging your 'scope unless you play safe and just explore low voltage battery-powered circuit for now. For example, build a 555 oscillator and use the oscilloscope to look at the signals from it. This is just an idea, others may have better suggestions.

shabaz  wrote:

 

As mentioned, you shouldn't be looking at the automated measurements such as Frequency, until you're comfortable with what you're looking at visually, the oscilloscope trace. And you need to get comfortable with the X and Y axes.

Thank you.  I did get the divisions figured out before you sent this.. 

There should be online video training on how to use oscilloscopes, and the manual should be read too.

I have watched couple of them and how I got to this point .  I am still working through the manual...

Your signal is a 60 Hz sinewave. There is no reason for the 'scope to display it's frequency in kHz, because although you may have expected 60kHz

I think this is what threw me off; I saw 60 and was thinking that was the correct 60.  My bad. It still doesn't show a change in frequency by varying R104 as the svc manual indicates on TP9 so something def wrong; unfortunately the "Yes" on the flowchart I think is supposed to be a "No" ..? which indicates replacing a chip that I don't think is available anymore: A100 or lCLM2917..

Hi Robert,

I don't know the answer to why you're not seeing the correct trace, but if it is 60 Hz, then it's extremely likely (99.99% confidence) to be the mains frequency. Since it is not possible for the mains frequency to be adjusted (it is what it is because it's due to the generator at the power station) so either the probe is in a different location to the flow chart, or incorrectly probing (e.g. perhaps the ground wire is not at the correct location either), or there's extremely severe multiple faults.

so either the probe is in a different location to the flow chart, or incorrectly probing (e.g. perhaps the ground wire is not at the correct location either), or there's extremely severe multiple faults.

Thanks, I do get both waveforms shown at each of those locations so I am pretty sure I am at least testing in the right places .  I still am not clear as I said in my original post whether the frequency counter that the svc manual says to use to measure the frequency and my scope work the same way. It may be the drive speed is not off and I will  just need to find another working drive in order to swap components until I hit on what is wrong.