Agilent DSO 3202A: DC Voltage Measurement Issue

[BulkHailing]

Hi all!

I recently bought used Agilent DSO 3202A scope and I’m trying to familiarize myself with the device, so I started with a simple measurements. The self-testing works well, and also measuring wave signal from the function generator also gives the expected result:





However when I  measure direct DC voltage from the power supply, i don’t understand the results. I expect the line to rise up to the point of the voltage value and stay there fixed like in this video https://www.youtube.com/watch?v=lhFTKEPhdnM.
When I touch the power supply output, the measurement “jumps” to the voltage level for a fraction of second, and then goes back to the center:


Also the same happens when I adjust the DC offset of the waveform on the function generator - the signal does not "move" up or down on the screen, it "jumps" and goes back to the center.

I performed factory reset to the scope, and i tried to change the coupling settings of the channel 1, but nothing seems to help.

Please help!

[Alex Nikitin]

Hi and welcome to the forum!

If you are getting the same results in both channels, I would suspect the probe you are using first of all. Do you have another probe? Try to use just a piece of a wire between the test signal output and the input , the test signal is 0 to +3V .

Cheers

Alex

[BulkHailing]

Yes, I tried to use different channels and I connected it through a wire also, the result is the same.
Test signal gives a square wave as expected, I have a problem only when I try to measure DC voltage. The scope seems to "react" to the change in the voltage, but it seems to be in some kind of mode when it only reflect change in the voltage, and does not measure the absolute value of the voltage, does this make sense?..

[Alex Nikitin]

Check if you have a digital filter engaged.

Cheers

Alex

[BennoG]

looks like the scope is locked in AC coupling.
do you hear relay's clicking when you switch from AC / DC coupling ?
Benno

[BulkHailing]

No, I don't hear relay switching when I change the coupling from DC to AC. Is there a way to unlock it?

[Alex Nikitin]

On these scopes there is no relay click going from DC to AC coupling and back (I have the 60 MHz version, DSO3062A in my lab and it doesn't click) . It does look however like there is a fault in that area as the waveforms are consistent with the AC coupling engaged. 

Cheers

Alex