Hi All,
this is my first post in the forum (although I have been following it for a couple of years)...
I acquired KEI2001 and found out it had noisy readings. Last digit (6-1/2 resolution, 1 NPLC, 20V range, no filter) is not stable, even if a stable signal (LM399 7V reference or short) is connected to the multimeter's input. This is confirmed by the internal self-test: error 200.2 (A/D noise) is reported...
I think the error is somewhere in A/D converter circuit (the error is reported even if the input buffer is disconnected and the input of A/D converter is shorted). I measured some signals in A/D converter circuit and found that CB and /CB signals were not clear (there was a ringing, see attached picture). Signals are generated by U812 (74HC74 - dual D-type flip-flop), so I suspect it could be defective.
Since there is a lof of knowledgeable and enthusiastic people in the forum, I would like to ask if someone could measure these signals and provide me a feedback - do they contain a ringing or not? I also attached a photo of my A/D converted board with signals locations.
Thanks!