My oscilloscope shows no voltage change (ABB Metrawatt M6001) - Page 1
Forum section: electronics / repair

author: PRAHL
author_rank: Newbie
timestamp: May 16, 2018, 09:15:01 am
content: Hi! Before I start I would like to state that my knowledge considering oscilloscopes is basically non-existing, but I am very eager to learn so I hope you guys can help me out!Two days ago I got an old analog oscilloscope from my dad. I have been using oscilloscopes two or three times before in school, no complicated measurements at all, just calculating frequencies and similar stuff. I thought that it would be a great way to increase my electrical knowledge and happily started "playing" around with it.I started playing around with a 9V DC battery trying to measure the voltage. Instead of getting 9V I got a little over three volts, which made me confused. I tried measuring a 12V DC charger that I plugged in my wall socket (maybe this was idiotic of me to do, considering I'm just playing around and don't really know what I'm doing) from which I also got way too low voltage shown in my scope. With the battery and the charger, both DC, I played around with the scope trying to learn the different settings.The day after when I plugged in my scope I was unable to get any voltage reading at all. Nothing. My question is, have I accidentally ruined my scope when measuring my 9V battery and my 12V DC charger or have I accidentally adjusted my settings some way? No matter what I do or which settings I change I cannot get a reading of voltage. All I get is a straight line in the window.After googling I found out how to calibrate my scope using the 2V output pin from the scope itself but my scope won't show any voltage change what so ever when I place the probe on the pin.Another thing that I think is weird is that when I choose CH1, without the coaxial cable plugged in, I get a change in voltage when I press the invert-button. Should it be like this? The height that the line jumps/drops when I press the button does not change when I change V/div, which also is weird?In my head, it should not make a change in voltage when I press invert if the scope does not measure any voltage?To be clear; I have not measured any AC-voltage and I have not measured any DC-voltage greater than 12V. Is it possible that I have ruined my scope using only 12V DC? Is there some easy way to check if it is broken or if it is some button that is pressed byt shouldn't?I have attached pictures of the scope, the different settings, the probes and also the change in voltage when I press "invert" without measuring anything.I would be very grateful for any answer, thanks in advance!Prahl

author: PRAHL
author_rank: Newbie
timestamp: May 16, 2018, 09:19:26 am
content: When I tried to do my measurements I had both V/div on 1, timebase on 0,1 and all three switches on DC. So not as in some of the pictures. Sorry about that, would have been better to take the pictures when the settings were set up as when I tried to measure.

author: oldway
author_rank: Super Contributor
timestamp: May 16, 2018, 02:06:39 pm
content: Welcome to the forum.Your oscilloscope is a rebadged HAMEG HM203-6.You can download the manual to learn how to use it.http://www.sm5cbw.se/hameg/hmosc/hm203-6-man.pdf

author: bob91343
author_rank: Super Contributor
timestamp: May 16, 2018, 05:11:44 pm
content: It's possible that you are on AC coupling, which will block DC from the display.The shift when pressing INVERT is normal; there are adjustments to minimize it. (DC balance)I doubt you have damaged the unit.

author: PRAHL
author_rank: Newbie
timestamp: May 17, 2018, 11:37:47 am
content: Quote from: bob91343 on May 16, 2018, 05:11:44 pmQuote from: oldway on May 16, 2018, 02:06:39 pmThank you for your answers and a special thanks for sending me the manual, I never would have gotten my hands on it otherwise. I have read through it and I'm gonna try again tonight. I'll get back to you to let you know how it's going!

author: PRAHL
author_rank: Newbie
timestamp: May 17, 2018, 07:48:35 pm
content: I just sat down with the scope for an hour or so, with no luck what so ever. I followed the first time use and calibration manual, but when I place my x10 probe on the 0.2V calibration eyelet nothing shows. And I still get no reading when trying to measure a 9V battery (which I measured 9V with a multimeter). When I place my probe on either + or - on my battery the trigger LED lights up (both with probe or earth). This makes me think that my cable at least is not broken. When I measure the resistance in my coaxial cable, not plugged in to my oscilliscope, I have 0,6 ohms from earth to the outside of my cable connection which sounds good to me. But when I measure from the tip of the probe to the inside of the cable connection I read O.L. does this mean that my probe/cable is broken?Do you have any other idea what can be wrong?While doing measurements I switched the AC/DC/GN to DC so I don't think that's the problemOnce again, thank you for your answers.

author: Chris56000
author_rank: Frequent Contributor
timestamp: May 20, 2018, 10:32:27 pm
content: Hi!You could indeed have a broken centre–conductor in your probe coaxial cable!The cables used to make oscilloscope scope probe sets are made with extremely thin wire, both for flexibility and to prevent excessive inner to outer capacitance which would degrade the signal at high frequencies!Buy a cheap switched x1/X10 Oscilloscope Probe Kit off fleabay, they will work fine if you follow the setting up instructions in the Manual carefully.If you get another probe and get exactly the same results, the oscilloscope itself could.be faulty!A quick test to try – set BOTH Ch1 and Ch2 to 0.05V or 0.1V/div, select "AC" on both channels, GENTLY tap a very thin screwdriver–blade on the centre hole of each channel input with your finger touching the screwdriver–blade (it's quite safe) – the scope will display a very rough and distorted waveform on the screen, what you are looking for is the waveform you see should be roughly the same number of vertical divisions in height for CH 1 and CH 2.If one channel gives a "waveform" very different in height to the other one then you'll need to try a more accurate test with a battery or the "Probe Test" terminal!Chris Williams

author: Electro Detective
author_rank: Super Contributor
timestamp: May 20, 2018, 11:47:41 pm
content: Greetings PRAHL, don't stress it mate, many of us have been 'there' with our first oscilloscope 'exciting' adventures...going southIf it's a brand new oscilloscope with a manual, chances are high you would get it going quite soon,but with a used unit it can be a different story and a bit of a gamble for the newbie to get it going,especially if any of the controls are sticky, dry, worn out in spots, crusty corroded connectors, suspect cables and probes,and too many controls in extreme positions including pullout Mag knobs and Hold Off positions, so the unit won't trigger and or produce any trace.At least you have a trace!I would suggest try to get some audio/music/radio signal into input 1 then input 2 with some cable scrap or adapter and start playing with ALL the controlstill you get a music/audio waveform jumping all over the screen, regardless of AC or DC selectionThe manual will give you a clue how to get there, but keep your attention on the Trigger Modes and what they do, and keep going back to them,because those are the main items to understand IMHO, otherwise the oscilloscope has no clue what you want to 'see' on that screenGood Luck and cool oscilloscope

author: tautech
author_rank: Super Contributor
timestamp: May 21, 2018, 12:31:43 am
content: Quote from: PRAHL on May 17, 2018, 07:48:35 pmUse the 2V Cal output and the input into the scope will be 1/10th of that (10x probe), therefore 0.2V and for that to show on the display even 2 divisions your vertical attenuator must be set to 100mV/div.So working backwards you must always remember your signal into the scope is divided by 10 using a 10x probe and make the preliminary scope settings based on what voltage you expect. Further, the 2V Cal signal is ~1KHz so a period of 1ms and to show the rising and falling edges of the squarewave nicely aligned to the graticules the timebase needs be set to 500us/div.If the probe still refuses to work just use a piece of wire between 0.2V Cal (remember no 10x division without your probe) and a channel input and the above settings will work just fine for you.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 21, 2018, 12:45:25 am
content: Just an observation about power supplies based on my experience...Sometimes the output voltage without the supply connected to its load will be higher than the specified value. I've seen 12VDC supplies give 16VDC without the load and 12VDC with the load. I've also come across something the hard/annoying way. I needed a 15VDC supply. I used a multimeter to confirm the output. Sometime later I hooked it up to my circuit while unplugged and then plugged it in. It destroyed my circuit. I looked at the output on my 'scope and discovered that when the supply first came on it gave a 60VDC surge! Also, it held quite a charge after being unplugged. Note that it was a linear power supply with a hefty transformer. I suspect a switching supply wouldn't do it. But now I know what to check for before hooking up a power supply that's lying around.

author: oldway
author_rank: Super Contributor
timestamp: May 21, 2018, 03:20:34 pm
content: Ask someone near you who knows the oscilloscopes to test it.Do not forget that there is a free course on the use of an oscilloscope that could help you a lot.https://www.eevblog.com/forum/beginners/oscilloscope-training-class-(long)/