Electronics > Beginners
[SOLVED] Weird behaviour in motherboard repair
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mlefe:
Hi guys, i'm trying to repair a laptop that has a fan that doesn't work.
When I measure resistance between an IC pin and the VFan_OUT pin on the fan connector I have a short (as expected) but when I connect the fan and measure again I can read more than 50K and raises until it OLs the meter (like if I was measuring a cap)... this is completely unexpected as I don't see how adding something can change the previous short... what am i missing? Thanks!
 
Shock:

--- Quote from: mlefe on April 22, 2018, 09:01:31 pm ---Hi guys, i'm trying to repair a laptop that has a fan that doesn't work.
When I measure resistance between an IC pin and the VFan_OUT pin on the fan connector I have a short (as expected) but when I connect the fan and measure again I can read more than 50K and raises until it OLs the meter (like if I was measuring a cap)... this is completely unexpected as I don't see how adding something can change the previous short... what am i missing? Thanks!

--- End quote ---

So are you saying, you're measuring a low resistance trace on the PCB and getting an odd measurement when you connect the fan?

Do you have a link to the schematic and is there any power/battery connected to the circuit or charged caps etc?
IanMacdonald:
Sounds like a residual voltage upsetting the meter.
amyk:
You have the leads touching something slightly different, and a cap is being charged up by the meter's test voltage.
mlefe:
I feel embarrassed, it was a very dodgy connection, nothing else  :-[ :-\

Thank you all!
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