Author Topic: Tek TDS7404 triggering issue  (Read 916 times)

0 Members and 1 Guest are viewing this topic.

Offline geshka

  • Contributor
  • Posts: 15
  • Country: ca
Tek TDS7404 triggering issue
« on: December 09, 2017, 08:18:14 pm »
Hello there.

I've been offered TDS7404 for fair price with one issue that I am observing with this scope - triggering is  funky. To be exact  - I am able to synchronize with test signal only on "rant"  mode.  External signals are difficult to synchronize and sometimes impossible at all. Is there definitive test for synchronization/triggering ? Would it be hard to fix if problem exist? what scope with in that condition would be worth ?

Thanks.
 

Online nctnico

  • Super Contributor
  • ***
  • Posts: 21145
  • Country: nl
    • NCT Developments
Re: Tek TDS7404 triggering issue
« Reply #1 on: December 09, 2017, 08:49:04 pm »
I'd apply a signal (from the probe calibrator output) set the scope back to default and use the auto setup. If that fails to get a stable trigger with a regular then it is safe to assume the oscilloscope has a serious problem. If you don't have a donor oscilloscope with a known good acquisition board I wouldn't spend a lot of money on it because an oscilloscope which can't trigger is basically worthless.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline geshka

  • Contributor
  • Posts: 15
  • Country: ca
Re: Tek TDS7404 triggering issue
« Reply #2 on: December 09, 2017, 09:28:32 pm »
Thanks for quick response, Nctnico.

This is exactly an issue... test signal (compensation meander in autoset) is jerky but not to the point when it is running away all the time - it is sometimes jumping left or right and  it is surely not rock solid like on my old trusty analog scope.  I am really confused and undecided.  and is that repairable if this is a problem?
 

Offline KE5FX

  • Super Contributor
  • ***
  • Posts: 1390
  • Country: us
    • KE5FX.COM
Re: Tek TDS7404 triggering issue
« Reply #3 on: December 10, 2017, 02:44:42 am »
One tricky aspect of fast DSOs is that if the trigger circuit is running at full bandwidth, it may see ringing and ground bounce on a low-frequency square wave that the acquisition system is hiding from you at slow sweep speeds. 

I'm not familiar with the TDS7404, but see if there's a lowpass filter option for the trigger (may be called 'HF REJECT' or something similar.)  In general, try switching to a much faster timebase than you would ordinarily use, and see if you see a lot of ringing/undershoot appear.  If there's an envelope or peak-detect acquisition mode, this may also give you a clue as to what the trigger circuit is actually doing.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf