Author Topic: AC Coupling Not Working in a Tektronix TDS420 (Quick Reference Guide Too!)  (Read 347 times)

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Offline Smoky

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During my last oscilloscope project, I learned how to test for AC ripple in the power supply circuit using three Tektronix oscilloscopes that I own. A 465B, a 222A, and a TDS420.

The TDS420 had problems.

So today I set the test back up as before to check the +300 VDC rail in a 310 oscilloscope project I'm working on.

I hooked the probe to the test point and I brought up the screen of the TDS420 where I choose between AC or DC Coupling.

No matter if I chose AC or DC, the +300 volt waveform remained the same on the screen. I did not hear any clicking noises within the TDS420 associated to any relay switching either. But I don't know if a relay is supposed to be heard or not anyway.

I tried this in all four channels of the TDS420 and the results were the same. No change in the waveform.

Two years ago, I replaced all of the electrolytic capacitors in the TDS420 and it always passes its self-tests and signal path compensation every time I use it. Maybe, AC/DC coupling isn't tested? And to let you know, every time I use this scope, I go to the menu where you can revert back to "factory settings" so that it clears any previous changes I have made in the past.

Being that this oscilloscope is without any available schematics, I can only hope that someone has experienced this before within their TDS series scope and found a way of repairing it.

Anyway, thanks for any help you can give me!







« Last Edit: February 04, 2020, 11:38:42 pm by Smoky »
 

Offline madao

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Re: AC Coupling Not Working in a Tektronix TDS420
« Reply #1 on: February 02, 2020, 06:22:11 am »
Press  channel 1 and then press  vertical menu.  You would found correct menu for ac coupling for channel.

What did you wrong?
You have enabled ac-coupling  into trigger-menu. You got it  AC-coupling trigger.

Greetings
matt
« Last Edit: February 02, 2020, 06:24:44 am by madao »
 

Offline Smoky

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Re: AC Coupling Not Working in a Tektronix TDS420
« Reply #2 on: February 02, 2020, 07:22:54 am »
Thank you so much Matt!



I even have the Tektronix TDS420/460 Quick Reference Guide and it does not show this menu  :o

Anyway, you made my night  :)

This is the AC ripple of a Tektronix 310 oscilloscope found on its +300 VDC rail.

This result falls in line with the other two Tek scopes that read the ripple.

James_s, if you catch this, what I'm using here with the TDS420 is a new Tektronix 1x P6101 passive probe. I also used it with the 465B and posted updated pictures of the results on the 310 Project thread. Boy, does it work well.

Have a great night!
 

Offline Smoky

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Re: AC Coupling Not Working in a Tektronix TDS420 (Quick Reference Guide Too!)
« Reply #3 on: February 04, 2020, 11:53:21 pm »
To all of the owners of the TDS420 and TDS460 oscilloscopes, I just had the 8-page Quick Reference Guide scanned at 600dpi and in color.

I uploaded the 30Mb file to Ebaman.com and it should be able to be downloaded within the next couple of days.

Thank you for all of the the help with my projects  :-+






 


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