Electronics > Beginners

Probes compensation issue?

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M84AB1:
Hi guys,

I recently purchased a Tektronix TAS 465 100Mhz Analog oscilloscope. It did not come with probes so I ordered a pair of Uni-T UT-P05 probes rated at 200Mhz from eBay. Now the problem that I appear to have is that I cannot perfectly compensate them. The input impedance of my scope is 1Mohm 20pf, and the probes capacitance at 10x is 20pF +/- 2pF with a compensation range of 15pF-30pF. The probes should therefore have no issues to compensate properly, but they don't.

I have attached pictures of RIGOL DS1052E probes and the UT-P05 probes. As you can tell RIGOL compensates perfectly without issues (RIGOL probe is the top signal)


1Khz


1Khz


10Khz


10Khz


23Khz


23Khz


50Khz


100Khz


200Khz

The Rigol probe (the top signal) only starts to look under compensated at 23Khz and beyond. Does anyone have any explanation as to what is going on? Maybe the Uni-T probes are just sh*t?

Some words of advise would be appreciated. Thanks guys.

alm:
Probe compensation is usually specified at one particular time base setting, a faster time base will always suggest under compensation due to the limited rise time of the signal. It does look like the Uni-T probe fails to compensate. There are definitely some crappy probes out there, these ones may either be lousy QC (both of them?) or lousy design.

Does the adjustment trimmer do anything? Is there only one or is there an extra HF adjustment that you may be adjusting? Any 1x/10x switch that may be in the 1x position? Not a whole lot you can do about it except complain to the seller. Modern probes are not usually designed to be user repairable.

vk6zgo:
Just to be dead sure,swap the probes between channels,& recheck.
If you have a faulty channel,you won't be able to adjust that out on the probe.

VK6ZGO

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