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Old 15th December 2012, 02:25 PM   #1
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Default TEK 2440 rippled !!?!

I recently bought a TEK2440 scope and it's hexibiting lot of rippling even when GND'ed. I cannot even have the probe calibration square wave "unrippled".

It apears on both channels. The Self Cal and the Self Diag routines are successful.

Is it a problem that's easy to fix?

See pics.

Regards,
MArtin.
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Old 15th December 2012, 02:52 PM   #2
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I have the same scope and it does not have that 'feature'.

Looking at your pix, that looks like noise rather than ripple so look for external sources of noise and\or interference. Make sure you have a good ground, move the scope to different locations and see if the interference changes. It is random rather than repetitive so it is not what you would call ripple in the classic sense.

I'll fire mine up today and see if I can figure anything out to help you.

Last edited by SteveJewels; 15th December 2012 at 03:08 PM.
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Old 15th December 2012, 03:24 PM   #3
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I agree it looks like parasitic HF noise. I tried in 3 different locations (3 buildings) with the same result. I wonder if theere's any filtering cap defective inside or something...

Beside that it's working good, but all my readings cannot be precise as that parasitic noises appear like ringing on real-world traces.

I'm just wondering if it's easily repairable or if I should just return it and wait for another opportunity.
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Old 15th December 2012, 03:31 PM   #4
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Bummer that it was not something easy. It looks to something internal.

I have no experience inside an o'scope so I can't be of much help to you.

I noticed that you had the coupling set to "ground", did you try "AC" or "DC"?
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Old 15th December 2012, 03:33 PM   #5
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They all show the same behavior. coupling set to GND should be dead quiet...
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Old 19th December 2012, 04:23 AM   #6
jtl is offline jtl  United States
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That's really quite surprising, and it's likely a power supply problem. There may also be a grounding issue in the chassis (a shield isn't connected properly). Depending on what you got it for, it should be repaired or returned, but I don't know that information :P
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Old 19th December 2012, 05:25 AM   #7
gootee is offline gootee  United States
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It looks digital; quantized to 40, 80 and sometimes 120 mV, in your first pic, and to one-tenth those levels in your last pic (which is at one-tenth the v/div of the first pic). So you have three LSBs of random noise, regardless of the V/DIV setting. Might be a clue as to where in the circuit the problem is.

If you don't return it, you should ask in the TekScopes group, at yahoogroups.com (after first searching their archive).

If you can easily return it, then you probably should.
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Old 19th December 2012, 05:34 AM   #8
Art M is offline Art M  United States
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Quote:
Originally Posted by canonnica View Post
I recently bought a TEK2440 scope and it's hexibiting lot of rippling even when GND'ed. I cannot even have the probe calibration square wave "unrippled".

It apears on both channels. The Self Cal and the Self Diag routines are successful.

Is it a problem that's easy to fix?

See pics.

Regards,
MArtin.
This is a complex Digital Storage Ocilloscope incorporating a unique CCD analog
storage register feeding an A to D system, storage, processing and subsequent D to A conversion for displaying on the CRT. Is this an easy problem to fix ? No, I think that you should have a look at the Maintenance manual. Pretty much all the answers here are simplistic in terms of solving your problem. You could start with a complete internal calibration of the unit (not the Self Cal or Self Diag routines).
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Old 19th December 2012, 11:52 AM   #9
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Quote:
Originally Posted by Art M View Post
You could start with a complete internal calibration of the unit (not the Self Cal or Self Diag routines).
Yes I think that's what I'll do. But until then, it's doing its job and for the purpose of testing only audio bands, it does the job just right.

Thanks for the advices.
Martin.
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Old 16th January 2013, 01:51 PM   #10
gootee is offline gootee  United States
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Did you find the problem or get the scope repaired?
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