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Background

I already have a (2nd hand) Philips PM 3253 oscilloscope. Although it has many features and is fast (50 MHz) the display is so bad, it's barely usable.

Therefore I bought another (2nd hand) oscilloscope, a Philips PM 3110 (2 channel, 10 MHz) with far less features). The display is much better.

Question

However, when I for example show a square wave on the oscilloscope, it is scrolling very fast, I have about 2 waves per square (cm). I tried moving the X position knob, but that only makes the left or right side being clipped/invisible.

And changing the X Magn. knob changes the scrolling, but in no way I can keep it more or less steady. I tried moving along the entire X Magn range and tried different Time Div. knob values.

What am I doing wrong? I see sometimes pictures of e.g. sinus or square waves which are not moving … or is that because a (very fast) picture is made?

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    \$\begingroup\$ Try changing the trigger level? \$\endgroup\$
    – SRR
    Commented Feb 6, 2019 at 21:59
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    \$\begingroup\$ You have to set the trigger to the channel you are sampling and play with the trigger level. \$\endgroup\$
    – Janka
    Commented Feb 6, 2019 at 22:00
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    \$\begingroup\$ @SimeonR I did not set a trigger level, I would check how it works on this oscilloscope, since it has only one knob for Time Div and the trigger settings are on that same knob. Thanks for the good direction. \$\endgroup\$
    – Michel Keijzers
    Commented Feb 6, 2019 at 22:11
  • \$\begingroup\$ Set trigger mode to Auto, rather than Normal. \$\endgroup\$
    – WhatRoughBeast
    Commented Feb 7, 2019 at 4:40

1 Answer 1

Reset to default
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There are several possible problems here:

  1. You haven't set the trigger properly. Make sure that the trigger mode selector is set to "HF", the source selector is set to an input that is active, and the trigger level is set appropriately.

  2. You may be expecting this to be a storage oscilloscope. It is not. It can only display a periodic signal which is currently being supplied to the instrument.

  3. The oscilloscope is broken. If so, throw it away -- this was an inexpensive instrument when it was made in the 1970s, and is unlikely to be worth repairing.

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  • \$\begingroup\$ Thanks for the answer … I will check the manual but don't have much time next two days, how to use the trigger, as it is not clear how to set it since the Time Div knob shares the trigger level. My PM 3253 was a storage scope but that one is quite bad (screen hardly usable). I give a continuous signal so in this case I expect I don't need a storage scope. And I doubt it is broken, I get steady 0 and 5V signals and in between (tested with a pot meter). I only have to recalibrate it maybe. \$\endgroup\$
    – Michel Keijzers
    Commented Feb 6, 2019 at 22:14
  • \$\begingroup\$ Luckily it was option 1. I don't know yet how I can set the trigger level, but I have now I steady/non scrolling image by using the square wave from the Probe Adj output. \$\endgroup\$
    – Michel Keijzers
    Commented Feb 8, 2019 at 20:41
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    \$\begingroup\$ You can ignore my comment about the trigger level. According to the manual I found, this oscilloscope doesn't have a trigger level setting (yikes). \$\endgroup\$
    – user39382
    Commented Feb 8, 2019 at 20:43
  • \$\begingroup\$ Ok thanks for the clarification ... I wish the display on the PM3253 worked better, because that oscilloscope is way more advanced. But at least now I have some oscilloscope. \$\endgroup\$
    – Michel Keijzers
    Commented Feb 8, 2019 at 21:22

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