Oscilloscope safety when connecting to an ATX motherboard

[Spun Ducky]

So one of the things I mainly want to use my slowly building tech bench for is repairing pc motherboards mainly ATX based for desktop computers. I just wanted to check what is the best way to insure the safe use of a rigol 1054z on a standard atx pc motherboard in regards to grounding?

[jcw0752]

As long as you are not trying to repair the ATX supply itself just tie your probe ground to mother board ground and probe away. The problem arises when trying to probe the ATX which is a Switching supply and has mains voltage that may not like the earth ground of your oscilloscope.
John

[Awesome14]

In regards to grounding yourself? the ground on the lead? And, unless you really understand what your doing, a scope like that won't help you with computer motherboards.

[Spun Ducky]

As long as you are not trying to repair the ATX supply itself just tie your probe ground to mother board ground and probe away. The problem arises when trying to probe the ATX which is a Switching supply and has mains voltage that may not like the earth ground of your oscilloscope.
John

So if I have a ATX motherboard connected to an ATX power supply that is powered on from mains voltage I just need to connect the ground clip on the oscilloscope to a ground point on the motherboard and it will be fine?

[imidis]

In all my years of computer repair desktop motherboards usually fail due to electrolytic capacitors, more common  failures are PSU/Fan, with the exception of maybe someone doing something not so smart and shorting things somehow. Laptops are much more prone to motherboard failure. Primarily because of heat and drops/abuse/spills.

Watch daves how not to blow your oscilloscope

[Fire Doger]

So if I have a ATX motherboard connected to an ATX power supply that is powered on from mains voltage I just need to connect the ground clip on the oscilloscope to a ground point on the motherboard and it will be fine?

Yes

In regards to grounding yourself? the ground on the lead? And, unless you really understand what your doing, a scope like that won't help you with computer motherboards.

He is repairing them, not designing them nor debugging them to need eye diagrams on DDR4. Rossmann does it without scope.

[TomS_]

Rossmann does it without scope.

And a lot of luck, trial and error, and educated guesses. 

[danadak]

These might help -





http://www.newark.com/pdfs/techarticles/tektronix/FFM.pdf


Regards, Dana.

[IanMacdonald]

Main point is to be careful where you put the probe flying lead croc clip. It is already connected to earth AND the computer case is likely earthed too. So putting it on the case or a mounting screw, no problem. Putting it on a point with a voltage could send a lot of current through your scope and damage it. (Computer PSUs can deliver up to 40A)

If there is no need for high accuracy then I often just tie the croc clip back to the probe coax and rely in the fact that the scope is already grounded. Or, put one probe croc clip on the case and use the other probe ungrounded. The only time this isn't ideal is when measuring small or fast signals, when having a local ground can make them cleaner. 

Other point, if using an uncapped probe beware that the metal ring behind the tip is grounded, and I couldn't count the number of times I've seen equipment blown up by a probe slip allowing this to short something out.    If you don't have a cover for it (the decent probe kits come with one)  put some tape round it.

HTH.

[james_s]

In case it's not clear already, the ATX power supply itself provides isolated voltages so if you stay out of that you don't have to worry about blowing up your scope. There are no dangerous voltages inside a typical computer and nothing is floating relative to ground. Just be sure to keep your fingers, probes, cables, etc out of the fans, I cut my finger pretty good by bumping a running CPU fan once.

[Spun Ducky]

Thanks everyone for giving great information and view points on the subject. I have taken some basic 200 level EE courses in the past but the actual hands on repair of professional devices is a lot to take in. I have lots more reading and videos to watch although I have watched Dave's video on oscilloscope safety quite a while ago and that is what even got me to ask this question. I figure asked the beginner question rather than destroy gear or hurt myself.

[Awesome14]

One thing about mobos, I've found they use high temp solder. You need a hot iron or you'll destroy the solder pads.

[Terry01]

Great reading and all well explained points. All put in laymans terms and very easy to understand. I am still very new too and having to learn all this. I just hope I put the knowledge into practise as easy! 

Thanks for sharing your knowledge to the experienced guys! Much appreciated.

[danadak]

When you are in doubt about ground loops do differential measurements.


https://www.tiepie.com/en/classroom/Measurement_basics/DifferentialMeasurements


https://www.picotech.com/library/oscilloscopes/differential-and-floating-voltage-measurements


http://in.tek.com/dl/3AW_19134_2_MR_Letter.pdf



Regards, Dana.

[james_s]

One thing about mobos, I've found they use high temp solder. You need a hot iron or you'll destroy the solder pads.

I don't think it's the solder, but rather the fact that they are multilayer boards with huge copper power and power planes. Copper is a very effective conductor of heat so you need an iron that can push a lot of heat into the pin you're trying to solder to keep up with the amount that is being carried away by the copper.