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Old 25th Feb 2021, 7:39 pm   #677
Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 7,538
Default Re: Non-working Commodore PET 3016

'Triggering' on a scope is where the scope holds the 'scanning dot' at the left hand edge of the screen until a specific point on the waveform being measured before letting it sweep across the screen. The idea is to get a rock steady picture by always starting the display sweep at the exact same point on the waveform.

You are using triggering already. On your most recent capture look at the top right hand corner of the oscilloscope screen. You see 'CH1' highlighted in yellow, to the left of that a picture of a 'rising edge', and to the right a voltage.

These indicate
-The scope is triggering when the signal voltage is rising, (rather than when it is falling)
-The scope is triggering on the signal on input channel 1
-The scope is triggering when the input signal rises past 3.76V.

Do you see the yellow arrow with a black 'T' at the right hand side of the screen? That is showing you the voltage level which the scope waits for the input signal to rise to before it starts the next sweep across the screen.

You should be able to click and drag that up and down to place the trigger level point at anywhere between the lowest voltage in the signal and the highest voltage in the signal. If you place it above the highest edge of the signal or below the lowest edge of the signal, the trace will lose lock and the signal will just look random.

To alter the vertical position of the channel 1 and channel 2 traces, look at your last capture again and this time look at the left hand edge where there is another yellow arrow marked '1'. That is indicating where the 0V base line is for channel 1. You can click and drag that to move it up and down the screen.

When looking at two DC signals such as the ones in the PET, one above the other, it would be usual to place the channel 1 0V base line on the thick middle line of the screen (the half way line) and the channel 2 0V base line on the bottom edge of the screen so that each signal has an equal amount of vertical space (four divisions) to be displayed in.

If you had the Volts/Div set to 1V/Div each trace would occupy up to five vertical divisions - 10 altogether - but you only have 8 vertical divisions on the screen, so to enable both signals to be shown on the screen at the same time without overlapping, you have to drop to 2V/Div so that each signal will be no more than 2.5 divisions high.
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