PMK German Probes X1000 strange defect - Page 1
Forum section: electronics / testgear

author: jonpaul
author_rank: Super Contributor
timestamp: October 17, 2023, 09:33:45 am
content: Bonjour, We have issues with some HV probes from the German probe firm, PMK.https://www.pmk.de/en/products/5_mm_hochspannungstastkoepfeUse 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 thanksJon PAUL

author: Gyro
author_rank: Super Contributor
timestamp: October 17, 2023, 11:52:55 am
content: 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 a4kV 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.

author: ebastler
author_rank: Super Contributor
timestamp: October 17, 2023, 12:45:39 pm
content: jonpaul's description, "MK PHV probes, X10002m2800V CAT IIPHVS-2000" suggests part no. 870-722-A00. Hence 4kV peak/pulse, but only 1kV CAT II.

author: Gyro
author_rank: Super Contributor
timestamp: October 17, 2023, 02:14:26 pm
content: 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.

author: TurboTom
author_rank: Super Contributor
timestamp: October 17, 2023, 08:44:35 pm
content: 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...).

author: jonpaul
author_rank: Super Contributor
timestamp: October 18, 2023, 05:07:57 am
content: Hello allthx for the notes:Further testsCOMP LF/LF trim on comp boxes work as expected.The bad probe scale factor adjust (middle) trim ofCOMP box changesshape of wave with change of attn factor : intermittent and scratchy as you trim.on good probe Resistance seen by scope at BNC is stable , on bad one resistance at BNC is lower and varyingCareful application of ISO alc into comp box trim does affect but does not fix bad probe.I have no gighometer at the moment, so I cannot measure the internal high meg series resistor, most likely 49 Megs.1/ Probes were working originally as a pair in differertial use. not exposed to excess voltages or mechanical abuse. Used in a normal lab well within ratings2/ All connections for return at BNC, probe tip return, ground clip are near zero Ohms. Only BNC is the Hameg German scopes input CH1/CHII which work fine and good quality. BNC segments on probe side are like new, no wear, corrosion or abuse.3/ The safety mark "2800VAC CATII" is on body of probes. (Also X1000) 2800 VRMS max = 4000 V peak.4/ PMK lists 4 types of X1000 PHVS that differ only in legnth (these are 2m) and presence of ID etc.5/ Contacted PMK, and recieved note from factory to send more info and scope pix. Have done that.Suspect the attn trimpot is intermittent OR that the HiMeg R 49M has failed.Impossible to open comp box or probe further.Awaiting PMK responses.Good day,Jon

author: alm
author_rank: Super Contributor
timestamp: October 18, 2023, 10:05:48 am
content: Quote from: jonpaul on October 18, 2023, 05:07:57 am49 MOhm is not exactly Gigaohmmeter-only territory. Do you not have a DMM that can measure up to 100 MOhm (not uncommon for bench meters), or a DMM that can measure conductance (Fluke 87/189 for example)? Or measure with 10 MOhm resistor in parallel and calculate back based on known value of 10 MOhm resistors. This is what many DMMs do for the higher resistance ranges.

author: jonpaul
author_rank: Super Contributor
timestamp: October 18, 2023, 02:29:33 pm
content: Update 18/10to Alm: re megohmeters:My main lab indeed has Keysight 34465A, GenRad 1863, 1864 megohmeters, Danbridge 0-30kV insulation tester etc.But now I am overseas with a very limited lab, VOM, scopes, Funct Gen, DCPS.I figured how roughly to test the probe resistance: Used a VOM 200 uA scaleThe SIGSALY Quantizer has +260VDC B+, I appled 260V to both probe tips.Measured the current flowing from the probe tip to BNC center and shield. About 4.7 uAboth good and bad probes. The HV series resistance is very close to the rated 50M Ohms.I conclude both probes series resistors are fineProblem is failure of the tiny and delicate scale CAL adjust trimpot.Hope for for PMK service.AmicalmentJon

author: jonpaul
author_rank: Super Contributor
timestamp: October 19, 2023, 07:43:14 am
content: Rebonjour,We attempted to use contact cleaner (a tiny drop) on the suspect gain trimpot of the defective PMK X1000 probe.The cleaning changed the waveshape but after LF comp adjustment the scale error is still 9 times, about the same:Photo 1 Scope Hameg HM203-4 photo of good (upper) /bad (lower) probe on same 2V 1 kHz CAL signal, scope CH1/CHII is 5 mV/DIVPhoto 2 Scope Hameg HM204 photo of good (upper) /bad (lower) probe on same 2V 1 kHz CAL signal, scope CH1/CHII is 5 mV/DIVSame result if the CH1/CHII is interchanged.Conclusion: As the probe series R is OK and the ground returns are near zero Ohms, we conclude that the Defect is inside the probe comp box, a bad gain trim adjust pot.Anyone ever seen this on PMK probes? Anyone ever opened or repaired a PMK probe comp box?I passed this on to the PMK Germany service, and await PMK's offer of repair or replacement.AmicalmentJon

author: HighVoltage
author_rank: Super Contributor
timestamp: October 19, 2023, 08:58:16 am
content: I had very bad experience with PMK 1000x Probes and killed a few of them without obvious reasons.Then I switched to TesTec X100 probes and never had a problem.TT-HV 250(I only needed this for up to 2kV)

author: jonpaul
author_rank: Super Contributor
timestamp: October 19, 2023, 09:09:49 am
content: Bonjour, HighVoltage:Many thanks for this note: "I had very bad experience with PMK 1000x Probes and killed a few of them without obvious reasons."Can you detail your "very bad experience" that killed them?As designer, and manufacturer of SMPS, HVPS, since 1970s, we used the classic Tektronix P6015, P6015A for decades, never any issues.We discovered the PMK X1000 probes recently thought to try a pair, as the PMK probe bodies and comp boxes are much smaller than the TEK.We find that the PMK X1000 probe tips, bodies and comp box trimmers are much more delicate than the TEK.We hope that PMK Germany service can support the bad probe and fix it.Amicalment,Jon

author: HighVoltage
author_rank: Super Contributor
timestamp: October 19, 2023, 09:22:55 am
content: Hello JonFor high voltage measurements of up to 40kV I also use the Tektronix P6015A and never had any problems with any of them.For anything above 40 kV and up to 80kV I use DIY capacitive dividers.For coil measurements of up to 2kV the P6015A probe was too bulky and I got the PMK Probes X1000 and one failed right away. I got a new one under warranty and that one failed after a short time. I tried a 3rd one and that one also failed and got returned for a refund. Since they all had warranty, I never attempted to open them for analysis.I switched to the TESTEC many years ago and and although they are only good for 2.5 kV, I never had a failure.

author: jonpaul
author_rank: Super Contributor
timestamp: October 24, 2023, 07:57:21 am
content: UPDATE 23 Oct 2023:Problem is definitely in the probe compensation box, most likely the scale/gain trimmer.I have received an RMA from PMK service, I shall return the defective probe to Germany soon.I have changed the post title as PMK support is fine!Shall update further after probe is returned to me.Jon