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Finding a short with canned air

chaka

chaka

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I recently repaired a VESC which had been shorted through the P1 header/encoder/hall sensor port.

The result was a dead vesc with a hot voltage regulator when powered on. I was short on time and my multi meter needed a new 9v battery so I resorted to less professional means of finding the culprite.

Using canned air, I sprayed the vesc making sure to invert the can, lightly frosting the VESC. Once powered on, you could see the short circuit clearly emerge as the heat generated thawed the frost, eventually terminating at the stm32 processor. After replacing the processor the VESC was back in full operation. :mrgreen:

34269bfeb3a9caad2e4497cd484cf821a06c292e_1_690x446.jpg
 
:D :D

As much as I applaud the ingenuity of the method I shudder at the execution.
Every electronically minded braincell in me is going @WTF?@ :shock: :shock:

But it worked, cool.
Don't try this at home kids...
 
WeeChumlee said:
:D :D

As much as I applaud the ingenuity of the method I shudder at the execution.
Every electronically minded braincell in me is going @WTF?@ :shock: :shock:

But it worked, cool.
Don't try this at home kids...
Click to expand...

I don't understand why you would shudder? Perfectly sound for a pcb this size.

[youtube]sglyFwTjfDU[/youtube]
 
We used to use liquid nitrogen in a similar way to the above, to troubleshoot assorted intermittent or otherwise unfindable problems (especially iffy SRAM chips) on various boards inside flight computers and displays, back when I worked at Honeywell CFSG.

I don't remember what they were called, but we used to use some form of dewar flask with a "spray" attachment specifically made for this sort of thing.

I dont' know how bad it was for the electronics, but it was an authorized troubleshooting method.
 
Liquid nitrogen is not conductive and if used properly, i.e. not to actually freeze the components, is a recognised way to do it. I have no problems with that. I don't think aviation authorities would condone usind canned air.
What you are freezing is just good old H2O. Pretty conductive and on uP with many pins so close together not something I personally would recommend. Not saying it does not work, just that it could possibly be potentially damaging.
In this case it worked and I am happy for Chaka that it did, I just hope that this does not lead to people without much electronic knowledge to follow suit as it could be more destructive than helpful. IMHO.
 
H2O is not conductive. Any H2O forming on the pcb would be condensed pure H2O and act as an insulator. The refrigerant used in canned air doesn't seem to conduct electricity either. While being sprayed it does build up a charge so it does have its risks. I wouldn't do this with an energized board but the ground was connected while I sprayed the pcb.

Also lightly frosting the board does not actually freeze the components. The thermal shock is not as high as you would think.
 
hehe
I am quite aware that "pure" H2O is not a conductor but water condensed from air out of a spray can, where carbon dioxide, or other impurities, may be present is probably not "pure".
This is why condensation is a problem in electronics. If it was always "pure" H2O then it would not be a problem, unfortunately in life very few things are pure.
If the "canned air" is specifically for electronics then it will be suitable, there are many forms of this stuff though, much of which is not suitable.
Like I said, done correctly this is a viable method. I just want to avoid any misunderstandings that may cause someone to actually damage their components.
(Closes brain again)
:D :D
 
I expect that most of the electrolytes present in the condensation on a PCB would be from residues on the board itself. I doubt frost would cause electronic failures, but it isn't completely out of the question. .
 
Perhaps a FLIR One would be a good tool for those troubleshooting electronics.
And it looks like a really cool gadget.
Has anyone here tried it yet ?

Actually this video is very relevant:
[youtube]xCf9ddrfykg[/youtube]
 
I used to work at an electronic repair shop in my early 20's. We used up-ended air cans all the time to freeze stuff. Sometimes you have a part that fails once it warms up a little or you just want to find the hot spot on the board. I've used the air-can method for years. It is possibly a problem if you live in a humid environment and you build up condensation on the parts, But that's easily dealt with too. Just turn the can over and blast it with the compressed gas rather than the liquid and you will blow away any water. OR just have an air compressor handy with a water trap on it.
 
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