Author Topic: Tektronix 2225 ringing issue (normal?)  (Read 473 times)

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Offline jero32

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Tektronix 2225 ringing issue (normal?)
« on: March 01, 2019, 11:22:33 pm »
Hello, I "repaired" a tek 2225 I got for free. However on the highest amplification range, there seems to be some ringing with the calibration signal hooked up. I was wondering if that was normal?
Here's a video of the problem:

If not normal, any suggestions on what might be wrong?
 

Offline tggzzz

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Re: Tektronix 2225 ringing issue (normal?)
« Reply #1 on: March 02, 2019, 12:13:26 am »
You are overdriving the amplifiers into non-linear regions, and they take a while to recover from saturation.

Tek scopes have a lot of overhead and recover well. Cheap modern digitising scopes are nowhere near as forgiving; if any part of the waveform is "off the screen", then be wary of what you see on the screen :)

The scopes with the best overload recovery are old scopes with sampling bridges in their front end. Except at the sampling instant, the amplifier is not connected to the input, is not being overdriven and so does not need to recover.

Summary: you are seeing normal operating behaviour. Congrats for testing and observing and questioning your understanding of the instrument.
There are lies, damned lies, statistics - and ADC/DAC specs.
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Offline jero32

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Re: Tektronix 2225 ringing issue (normal?)
« Reply #2 on: March 02, 2019, 12:22:12 am »
Good to know. I'll have to calibrate it a little better sometime in the future when I have access to better equipment. But it's nice to know I don't have to "fix" anything.

Thanks for the help!
 

Offline David Hess

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Re: Tektronix 2225 ringing issue (normal?)
« Reply #3 on: March 03, 2019, 01:11:17 pm »
That looks normal for when the input is overdriven.  Note however that the probe calibration signal from the oscilloscope is flat but not necessarily clean on its leading edge.

You could use the position control when the signal first shows signs of overload and see if the shape of the leading edge changes with position on the screen which is a sure sign of overload.

Check out Linear Technology application note 79 for a discussion of oscilloscope overload performance.
 


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