TDS754 Vertical Input Coupling set to GND


Mike Lemcke
 

I have purchased a TDS754 scope. Self Tests PASS. When I went to the Vertical Menu and then to Coupling, I pressed the GND button. Instead of getting a Horizontal Flat Line at the CH1 marker, I saw noise. It is the same on all 4 channels. The DC and AC inputs are fine.
I have read the TDS754 User and Service Manuals, but they are not clear about seeing a flat line when set to GND.
I have a TDS224, have used a TDS2000 series scope at work and I contacted a friend who uses a TDS2000 series scope. They all produce a flat line when set to GND.
Should a TDS754 produce a Flat line when the Vertical Input Coupling is set to GND?
I would like to know if this the way a TDS754 works because I can return the scope if this is a problem.


Siggi
 

All scopes exhibit some amount of noise at all times, even in GND coupling.
The amount of noise you see will depend on the vertical attenuator setting,
the bandwidth of the scope, and the display settings.
If you enable the 20MHz bandwidth limit, the noise should drop, and the
noise should be greatest at the most sensitive vertical settings.

See e.g. this video https://youtu.be/Znwp0pK8Tzk for some background.

This being said, your new scope may well be exhibiting excessive noise, or
there may e.g. be power supply ripple bleeding into your traces. It’s hard
to say from your description.

Maybe if you upload some pictures, it’d be easier to say.


Þann lau., 18. sep. 2021 kl. 05:03 skrifaði Mike Lemcke <mlemcke@wi.rr.com>:

I have purchased a TDS754 scope. Self Tests PASS. When I went to the
Vertical Menu and then to Coupling, I pressed the GND button. Instead of
getting a Horizontal Flat Line at the CH1 marker, I saw noise. It is the
same on all 4 channels. The DC and AC inputs are fine.
I have read the TDS754 User and Service Manuals, but they are not clear
about seeing a flat line when set to GND.
I have a TDS224, have used a TDS2000 series scope at work and I contacted
a friend who uses a TDS2000 series scope. They all produce a flat line when
set to GND.
Should a TDS754 produce a Flat line when the Vertical Input Coupling is
set to GND?
I would like to know if this the way a TDS754 works because I can return
the scope if this is a problem.






EricJ
 

How much noise are we talking about, and in what vertical range? Both of my 754s produce as flat a line as they're going to when ground coupled but there will always be some noise present. If we're talking a barely squiggly line that doesn't even deviate a unit from the baseline it's likely nothing to worry about. Of it's deviating by divisions, you obviously have a problem. Give us the vert range, set a min/max measurement and see what you get. As the other fellow said, not enough information.--EricSent from my Galaxy

-------- Original message --------From: Mike Lemcke <mlemcke@wi.rr.com> Date: 9/18/21 4:03 AM (GMT-06:00) To: TekScopes@groups.io Subject: [TekScopes] TDS754 Vertical Input Coupling set to GND I have purchased a TDS754 scope. Self Tests PASS. When I went to the Vertical Menu and then to Coupling, I pressed the GND button. Instead of getting a Horizontal Flat Line at the CH1 marker, I saw noise. It is the same on all 4 channels. The DC and AC inputs are fine.I have read the TDS754 User and Service Manuals, but they are not clear about seeing a flat line when set to GND.I have a TDS224, have used a TDS2000 series scope at work and I contacted a friend who uses a TDS2000 series scope. They all produce a flat line when set to GND.Should a TDS754 produce a Flat line when the Vertical Input Coupling is set to GND?I would like to know if this the way a TDS754 works because I can return the scope if this is a problem.


Mike Lemcke
 

Thank you to Siggi and EricJ for responding. The youtube link was very helpful. I now understand what I am seeing.