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| PMK German Probes X1000 strange defect |
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| jonpaul:
Bonjour, We have issues with some HV probes from the German probe firm, PMK. https://www.pmk.de/en/products/5_mm_hochspannungstastkoepfe Use two PMK PHV probes, X1000 2m 2800V CAT II PHVS-2000. One probe is perfect, but the matching second probe has distorted waveshape (even on 1 kHz CAL square) and about 100 ratio not the marked X1000! We thought a loose or oxidized connection but it is not. The resistance at the bad probe BNC is flaky, varying and lower than on the good probe. We tried these on several Hameg scopes (HM203, HM204) and channels 1/2, it is definitely the probe. We tried to adjust the LF/HF/DC trim on the compensation box, the LF/HF work but does not fix it. The DC trim (middle) is flaky. PMK Germany has offered an RMA and good support. Any PMK probe users or PMK staff contact, your advise is appreciated. Many thanks Jon PAUL |
| Gyro:
Surely a higher than expected amplitude, coupled with a lower than expected resistance at the BNC can only point to breakdown and reduction in value of the main tip series resistor. That sounds like a very bad thing in a 4kV pk [EDIT: I only see 2kV and 4kV pk rated probes on the linked page, not 2.8kV - Which is it? A 2kV probe that has been exposed to 2.8kV or a 4kV probe?]. If this is the case then it is not very surprising that the trimming does not function correctly. I think return / scrapping is your only safe option. |
| ebastler:
jonpaul's description, "MK PHV probes, X1000 2m 2800V CAT II PHVS-2000" suggests part no. 870-722-A00. Hence 4kV peak/pulse, but only 1kV CAT II. |
| Gyro:
Thanks ebastler, I didn't look that closely at the page beyond noticing the 2kV and 4kV models. I don't think it changes my diagnosis (tip resistor starting to break down), that should never happen. |
| TurboTom:
To me, it rather looks like a flakey ground connection of the BNC or the probe cable. Please try connecting the ground at the probe tip and have a good look at the segmented annular grounding contact of the BNC. It may be necessary to carefully pry the segments slightly outward so they have a decent spring force against the BNC(F) ground "tube". I've got some SMA/BNC adapters that only after this procedure work properly (of course, the were of the "el-cheapo" variety...) ;D. |
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