Author Topic: Analog oscilloscope problem  (Read 587 times)

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Offline stev.dk

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Analog oscilloscope problem
« on: May 16, 2013, 03:58:06 PM »
 :-BROKE

On normal working mode (real time mode?), theres no problem. When i press the store button, an insane amount of noise is displayed on the screen. On a square wave or a static signal (like 5v), im able to remove most of the noise (almost all noise left, is when the signal changes) using the pot for setting the vertical position, and the balance trim pot. Even tapping the pot seems to make a difference. At some positions the signal is present, but overloaded with noise - at other positions, theres nothing but noise.

Sometimes when im trimming the pots, it seems like the whole display is flickering, so a noise peak, that was present 50ms ago, is now gone and visa versa (a clean signal 50ms ago, suddenly have noise).

So i think it might be the signal coming from the store function to the display, that is somehow getting contaminated. Does this sound legal, or did any of you guys have a simular problem, that was caused by something else?

The scope is a gould os-1420, theres a user/service manual here: http://www.mr2.net/marknias/gould1420.pdf

Please note, theres nothing wrong with the probes or the input signals.
Crank it up till' everybody's ears are bleeding, then just back off a notch.

Offline stev.dk

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Re: Analog oscilloscope problem
« Reply #1 on: May 18, 2013, 07:25:01 AM »
Ok so this is wierd...

I took the cover off, and put the scope on its side to make some measurements. I only got around to measure one voltage line, and the problem vanished. Without putting the cover back on, i turned it on its right orientation, and the problem came back. I once again put it on it's side, and again it was working perfectly. Slowly turning it to it's right orientation... and it still works.

I havn't been able to reproduce the problem since, but im sure it will return eventually - anyway i put the thing back together. Im waiting for my new multimeter to arrive, so i can do a "service" on the thing.... At least as far as the manual goes, and do some further checking for intermittence.
Crank it up till' everybody's ears are bleeding, then just back off a notch.

Offline madires

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Re: Analog oscilloscope problem
« Reply #2 on: May 18, 2013, 07:35:23 AM »
Bad solder joint?

Online PaulAm

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Re: Analog oscilloscope problem
« Reply #3 on: May 18, 2013, 07:54:40 AM »
I'm not familiar with that scope, but I had a problem that appeared only when tapping the scope.  Finally tracked that down to a cracked ceramic substrate resistor.  Drove me nuts trying to find that one.  Try tapping around or freeze spray.  Sometimes thermal shock will open an intermittent.


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