Electronics > Beginners
How to check live voltage value in circuits with an analog/digital meter.
Serge125:
Hi all and Mr. EEVblog. For as long as I can remember I would like learn how to check voltage on a live circuit but I've looked every where in books, vids etc.... for any detail on how to do this and I just can't find this. I remembering a long time ago I did poked on a live circuit and fried something and since then I have never poked on live circuit because I'm afraid to short something and make things worse. Mr EEVblog you have a MASSIVE vid collection on YT, but I don't know if you have one that explains how to check live voltage values on circuit boards BUT if you do can you tell me the link so that I can watch it. I wanted to fix an old Amiga HD and I asked what I could do and one guy said to check voltage at a certain part for a 5V signal and I told him that I didn't know how to do this and he never answered me. I REALY like to fix things and electronics is something that I truly enjoy doing (when I know how to do it on some problems) but when I ask people for help they just ignore me and I thought that in a blog we are all here to help and learn. I hope this place I will finally get some answers because up to now I never did find any where that wanted to help me so that I can grow my knowledge of electronic repair. Thanks for reading and hope to get news from you all!!
Serge
andy3055:
May be you can learn from one of these videos:
https://www.youtube.com/results?search_query=how+to+use+a+multimeter
AVGresponding:
Without looking through all those videos, I can't say for sure, but there are a few things that are often not mentioned in these types of tutorial.
1. Use sharp probes! Blunt probes will slip while you are trying to measure something and at best annoy you, at worst, short something out and damage it.
2. Use shrouded probe tips; these minimise the risk of accidentally bridging conductors/component legs.
3. On boards with a high density of components/traces (likely on something like an Amiga HD, old as it is), it might be a good idea to try and trace out the point you want to measure to a more accessible point, assuming it's not a designed test point. Failing that, it might be possible to solder a fine wire to the point you need the live measurement from, so that you can do it without risking a costly probe slip.
4. Use antistatic precautions! Most components are safe from the levels of ESD you might find in a hobbyists workshop while they are in circuit, but not all of them. If you're not sure, treat it as sensitive and needing protection. Some complete circuits are static sensitive also. Technically all semiconductors are sensitive, but usually discrete components like BJTs for example have layers so thick the damage is insignificant unless extreme and/or repetitive. Still it's good practice to always follow antistatic procedures, and won't hurt the DUT.
Happy testing!
SL4P:
At a very fundamental level, any voltage you will measure is at a potential with reference to some other point of the circuit...
Usually 0V, or often that’s tied to GROUND, but [WARNING] you can’t guarantee that.
Consider that some voltages may be AC, so your readings, method and range of measurement will be different from DC measurements.
And finally, do your research on WHAT you’re probing. mains-level voltages (AC or DC), can kill you in a dozen different ways.
pcmad:
when working on live i always use an isolation transformer
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