Oscilloscope Random Flicker - GW Instek GOS-6112

[michaelr]

So, I just picked up a used GW Instek GOS-6112.  The seller claimed it had been tested, but right out of the box the screen flickers .

It doesn't appear to flicker at all when first powered up.  It is only after about 1/2 minute, that the screen begins to blink out completely, 3-5 times a minutes, or so.  Sometimes in rapid succession, or once every 10-15 seconds.

I'm thinking this could be something that occurred during shipping and am considering fixing it, if it is something simple.  Otherwise, I will likely return it.  This is my first oscilloscope; and am just wading into electronics. 

Any thoughts?   Thanks!   

[michaelr]

Correction.  Actually, upon another inspection, it is the cursors that are flickering.  The readout is stable.

[michaelr]

Ok...  Those weren't the cursors...  They are the Ch1/Ch2 inputs signals, without any probes attached to the Oscilloscope.   I guess I should have read the manual first.

I'm going to figure out how to use these humdinger probe leads and see how it responds with household line voltage.

[NeedsMoreFlux]

Does it flicker only when you move the mouse?

What happens if you unplug the mouse, does it still flicker?

Have you looked for bad solder joints, bad caps, or overheating components?

[StillTrying]

I'm going to figure out how to use these humdinger probe leads and see how it responds with household line voltage.

Don't.

[Armadillo]

BANG! BOOM!
It will blow up your scope!
Stop and read the post "Scope Blow, WHY?"

[michaelr]

Thanks, but It seems to be fine.

I simply mistook the trace of what appears to be noise being picked up from the ambient, without any probes connected, as the cursor. It appeared to be a solid horizontal line, that flickered randomly.  When testing the new probes, bought separately, using the calibration signal, the scope appears to be operating okay.  Yeah!

It may need some tweaks to its' calibration.  If anyone may know where to find a technical manual, this may be helpful in the future.

[michaelr]

BANG! BOOM!
It will blow up your scope!
Stop and read the post "Scope Blow, WHY?"

Thanks StillTrying and Armadillo for the save.  I did not test mains power with Oscilloscope; and checked out the post "Scope Blow, Why."
https://www.eevblog.com/forum/repair/scope-blow-why/

Lots to learn!

[Armadillo]

You are welcome.
Do also watch the electric shock video there... 

[michaelr]

You are welcome.
Do also watch the electric shock video there... 

Yes, I saw the video you posted there.  It is quite the sober reminder, to be cautious around high voltage; and could save a life.  Learning from you own mistakes pays poorly in this field.

[michaelr]

The "flicker" turned out to be a 4mVp-p/60Hz AC signal humming on my input channels.  My mains power is 120V/60Hz.  As I've now read the 'Scope Blow, why?' topic thread and watched the videos, I would hazard to guess the signal is coming from the local mains ground/neutral bus, via the scope's power cable ground connection, which is also used as the input signal ground.  This could explain why it manifested as a signal trace, even without the probes being connected.

[Armadillo]

Well, connect your input to ground through the oscilloscope input selection knob/level and see if the noise is still there.
It should just display a straight line with no noise.

[james_s]

The first step with any sort of thing like this is slow down and read the manual, learn how to properly use the equipment before assuming something is wrong. I've bought "broken" equipment before that turned out to work fine, the seller just didn't know how to use it.

[michaelr]

Well, connect your input to ground through the oscilloscope input selection knob/level and see if the noise is still there.
It should just display a straight line with no noise.

Absolutely correct.  The noise goes away with the input selected to ground.  It turns out the signal is not present when the probes are disconnected also.  The trace is simply a solid line, as you said.

Thanks for the pointer!