DS1054z probe problem? - Page 1
Forum section: electronics / beginners

author: huu_tri0101
author_rank: Contributor
timestamp: March 29, 2015, 06:29:41 pm
content: I'm new with oscilloscope. So I have a lot of thing have to work on. So please help me.After got my DS1054z, I hook the probe RP2200 (comes with the scope) to my 18V 5A DC power supply output (set 5.5V) to take some measurements, after 5 min the end of the probe get warm. After that, I hook it to test point on the scope and it doesn't work any more (doesn't show any signal). I tested the scope with other probe, everything works fineSo Did I do anything wrong?

author: wraper
author_rank: Unknown
timestamp: March 29, 2015, 07:05:08 pm
content: Unless there was connected low resistance load to the BNC connector of the probe while probe being set to x1 mode, unlikely that you could do something wrong.

author: miguelvp
author_rank: Super Contributor
timestamp: March 29, 2015, 07:37:11 pm
content: Where did you hook the ground of the probe to?Probably there is a voltage difference between the scope ground and where you placed the ground clip.I'ts always a good to measure to see if there is any voltage between your scope ground and where you are about to hook the ground clip.

author: huu_tri0101
author_rank: Contributor
timestamp: March 29, 2015, 09:06:11 pm
content: Quote from: miguelvp on March 29, 2015, 07:37:11 pmBoth the scope and the DC power supply are not ground connected.I just did measurement the difference voltage between BNC's ground and negative output with Fluke 87V, it shows 14VAC.I still don't understand what happen.

author: huu_tri0101
author_rank: Contributor
timestamp: March 29, 2015, 09:08:49 pm
content: Quote from: wraper on March 29, 2015, 07:05:08 pmCould you please explain more, I'm still confusing.Thank you

author: miguelvp
author_rank: Super Contributor
timestamp: March 29, 2015, 09:19:40 pm
content: Quote from: huu_tri0101 on March 29, 2015, 09:06:11 pmWatch this video by Dave:

author: max666
author_rank: Frequent Contributor
timestamp: March 29, 2015, 09:41:28 pm
content: Measuring 14VAC between grounded and none grounded points, with a multimeter, may not say very much, because of the high input impedance of a general multimeter (10 MOhm). That 14VAC could be just because of stray capacitance inductance coupling bla bla ... if you connected a 12V lamp between it, it probably wouldn't light up and the voltage would drop to zero. If it does light up and the voltage doesn't drop, then you got a problem and this could be very well a reason for the probe to get warm, because then current is flowing through the ground lead of the probe.What wraper meant is that a scope probe on x1 is basically a pair of wires:so if you connected the BNC of the probe to anything other than the input of a scope (1 MOhm input impedance), then there could also flow current that shouldn't flow.

author: huu_tri0101
author_rank: Contributor
timestamp: March 29, 2015, 10:15:21 pm
content: To max666:Both the scope and the DC power supply are not ground connected. The outputs of DC power supply are isolated.when the probe's on X1 mode is basically a pair of wires but inside the scope has the 1 Mohm resistor so how could the massive current can flow to damage the probe?Sorry, I really don't know what wrong.

author: wraper
author_rank: Unknown
timestamp: March 29, 2015, 10:28:22 pm
content: Quote from: huu_tri0101 on March 29, 2015, 10:15:21 pmTherefore I said unless something low resistance on BNC, like 50 ohm terminator. Maybe it sounds stupid stupid but one forum member tried this. Attached 50 ohm terminator and probed PSU at x1 mode. BTW measure resistance with multimeter. Probe ground to BNC ground and probe tip to BNC center pin in x1 and x10 switch positions.

author: tggzzz
author_rank: Super Contributor
timestamp: March 29, 2015, 10:42:30 pm
content: Quote from: huu_tri0101 on March 29, 2015, 10:15:21 pmYoureallyneed to watch and understand Dave's video - preferablybeforeyou injure yourself or someone elseHint: the probe shield is a continuous wire. The current didn't go through the 1Mohm resistor.

author: max666
author_rank: Frequent Contributor
timestamp: March 29, 2015, 11:00:46 pm
content: Quote from: huu_tri0101 on March 29, 2015, 10:15:21 pmIf the outputs of the DC power supply are isolated ... ifKeep in mind that once you connect one of the ground leads of one of the probes of your 4 channel scope, the power supply isn't floating any more ... watch Dave's videoWe don't know what's wrong either, we're just listing possible mistakes.There's also the remote possibility of a faulty scope probe. Do you have a multimeter? I hope so! Measure the resistance between probe tip and ground lead, like wraper suggested.

author: miguelvp
author_rank: Super Contributor
timestamp: March 29, 2015, 11:04:45 pm
content: Even if they are isolated, say you have an ethernet cable hooked to your scope, now it's mains earthed, same goes with a usb cable.Edit: maybe not with the ethernet cable but definitely with the USB one.

author: huu_tri0101
author_rank: Contributor
timestamp: March 30, 2015, 03:37:55 am
content: Did I do anything stupid?

author: han
author_rank: Frequent Contributor
timestamp: March 30, 2015, 04:52:06 am
content: probe sanity check:unplug the probe, and check for resistance between inner and outer connectorit should be open (more than 10Mohm)

author: Monkeh
author_rank: Super Contributor
timestamp: March 30, 2015, 05:06:35 am
content: Quote from: huu_tri0101 on March 30, 2015, 03:37:55 amYes, the whole not connecting CPC to a class 1 appliance thing.

author: huu_tri0101
author_rank: Contributor
timestamp: March 30, 2015, 07:18:27 am
content: Quote from: han on March 30, 2015, 04:52:06 amI did it and it shows only 60 ohm.

author: tggzzz
author_rank: Super Contributor
timestamp: March 30, 2015, 08:42:38 am
content: Quote from: huu_tri0101 on March 30, 2015, 03:37:55 amYes! You have donetwostupid things.First, you connected up a scope without understanding what you were doing. That mistake can be forgiven, and doesn't necessarily mean anything about the future.Second, and more importantly, it appearsyou refuse to look at the answer and at safety informationthat people have given you. That mistakecannot be forgivenbecause suchdeliberate stupidity and ignorance implies you willcontinueto put yourself and other people in danger for the rest of your life. Is that what you want?Hint: look athttps://www.youtube.com/v/xaELqAo4kkQas suggested by miguelvp.

author: tggzzz
author_rank: Super Contributor
timestamp: March 30, 2015, 08:45:18 am
content: Quote from: huu_tri0101 on March 30, 2015, 07:18:27 amThat's not exactly a surprise: you melted the insulating plastic.What did it measure before you overheated it in the way described inhttps://www.youtube.com/v/xaELqAo4kkQ?

author: huu_tri0101
author_rank: Contributor
timestamp: March 30, 2015, 09:59:58 am
content: Quote from: tggzzz on March 30, 2015, 08:42:38 amFirst, I want to say thank you a lot for your answers. It's really mean a lot.Second, I don't refuse to look at the answer, really I don't know what was wrong. So please forgive me that I made you think I like what you said. So please help me.Before I purchase my scope, I watched Dave's video 2 times. Because $400 is really a big money for me, so I don't want to blow it away.I see that what I did (explain in my drawing) doesn't in any case can blow my scope that Dave mentioned in video.The scope are not grounding, the output of DC power supply are isolation. The probe's clip connect to "-" output.So please help me. I really don't know why.

author: tggzzz
author_rank: Super Contributor
timestamp: March 30, 2015, 03:44:43 pm
content: Quote from: huu_tri0101 on March 30, 2015, 09:59:58 amI cannot explain this topic any better than has been done in the video. If you don't understand what is in the video then you must stop and wait until someone teaches you what it means.Nobody will diagnose a safety issue remotely. There is too high a probability that you have not explained everything (because you don't know what you are doing!), or that we would miss a vital clue as to what's wrong, or that we would misunderstand what you are saying.Your best bet is to get somebody local to look at what you are doing, and to measure everything relevant before you connect things up again.

author: huu_tri0101
author_rank: Contributor
timestamp: March 30, 2015, 04:49:07 pm
content: I have some mistake in my drawing. So please take a look of a new one.The outputs of DC PS ("+"&"-") are floating. So there is no change that I can't short out the circuit.So I don't see what I did wrong. So what going on with my probe.to tggzzz:I really love your help.

author: aveekbh
author_rank: Regular Contributor
timestamp: March 30, 2015, 05:13:59 pm
content: Quote from: huu_tri0101 on March 30, 2015, 09:59:58 amPleasedo notuse a scope in this way! It is not safe for you.Quote from: tggzzz on March 30, 2015, 03:44:43 pmAbsolutely. Try to get some local help.Some hints/ideas for sanity checking:Use a multimeter to check that the output of the power supply is really floating. Measure the resistance from the output terminals to mains earth pin (on the connector). Don't rely on the disconnected earth wire. It is not safe!Use a multimeter to check that there isno continuitybetween the power supply terminals and the scope BNC shell (which should be connected to mains earth).

author: huu_tri0101
author_rank: Contributor
timestamp: March 30, 2015, 05:23:53 pm
content: Quote from: aveekbh on March 30, 2015, 05:13:59 pmThank for your help.I did check all of them, so I'm sure that they are floating and no continuity between the PS terminals and the scope BNC shell.So I did what I did again (the same way that I screw up the probe before) with another probe , everything fine, the probe doesn't get hot. So what happen with the first probe? I checked it worked before with the test point on the scope

author: kezat
author_rank: Contributor
timestamp: March 30, 2015, 05:45:41 pm
content: Did you at some point have 2 or more probs in use with the ground connected at different potentials? remember that the ground leeds will act as a short to one another. Also this setup your describing might not be what caused the damage to the prob in the first place, 60ohm short could start to get warm.Photos speak volumes, take some photos of your setup.What did you do to break the ground connections? (bad idea btw)

author: klr5205
author_rank: Regular Contributor
timestamp: March 30, 2015, 08:43:35 pm
content: Quote from: kezat link=topic=45334.msg640891#msg640891 date=1427737541What did you do to break the ground connections? (bad idea btw)[/quote

author: miguelvp
author_rank: Super Contributor
timestamp: March 31, 2015, 12:11:44 am
content: But that will probably be touching the screw and that is probably earthed.Without being there we can't know what is going on. diagrams are just that, diagrams.

author: Nerull
author_rank: Frequent Contributor
timestamp: March 31, 2015, 04:14:33 am
content: The only thing not grounding your scope but leaving it connected directly to hot and neutral accomplishes is to make it far more dangerous for you and any circuits you connect it to. I once saw a PC chassis sitting at 60V to ground because it was plugged into an old outlet with a bad ground connection. You could be connecting that to your circuits.

author: aveekbh
author_rank: Regular Contributor
timestamp: March 31, 2015, 03:20:50 pm
content: Quote from: Nerull on March 31, 2015, 04:14:33 amThe EMI suppression capacitors at the mains input to any Class 1 device (basically anything with a protective earth connection) form an AC voltage divider if the earth is removed. This will bring the chassis to half the mains voltage - 120 V in this case (the OP is in Vietnam according to the flag).Source:http://en.wikipedia.org/wiki/File:Safety_caps-Appliance_Class_I.svgThat is why it's really dangerous to remove the earth connection from the scope. Show us a photo of your setup and think of another way to do the measurement.