Evaluating Noise on Tektronix TCA Differential Probes

[calibrationfixture]

Hi to All,

Some time ago I acquired a few Tektronix TCA Differential Probes. They all pass the Standard Tests, but the only two P7380 Probes show intriging noise results.

One of them has a little DC-Offset with open inputs, The other not. When shorted to ground both Probes have no DC-Offset. On both I observed with 5x Attenuation and highest TDS7404B Sensitivity (thus 10 mV/Div on Scope) a little drifting Noise-Baseline (Burst/Pop-Corn Noise?) in comparison with the other Differential Probes (P7330 and P7380SMA). Is that normal for P7380 Probes? Even more strange on one of the P7380 Probes (with signs of repair!) there is no difference between Noise Measurement Values (Vpp and RMS) with open or shorted inputs. Anybody with some clues on this?

Calibrationfixture

[KrudyZ]

Count yourself lucky if that is the only problem you have with a 8 GHz diff probe.
These probes are not very robust.
I have a couple where one input is blown.
They are also basically not repairable.

[David Hess]

One of them has a little DC-Offset with open inputs, The other not. When shorted to ground both Probes have no DC-Offset.

Offset when open is caused by excessive leakage, which is usually from overload damage or ESD.  If the leakage is across a PN junction, then it produces the same current noise as input bias current does.

[calibrationfixture]

Hi David,

Thank you for your reply. Reading the User Manuals of these Probes and how they are configured (Service Manuals) there seems no problem (= damage) when there is a little (steady nature, thus not drifting) DC-Offset on highest Sensitivities in case of open inputs.

Calibrationfixture