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Tested dead laptopís motherboard with multimeter -results


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#1 cumputer

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Posted 10 May 2018 - 04:19 PM

(This sites ridiculous, wont let u copy your post before switching to full site mode, then doesnt save your draft once switching, and its a computer site.)


So i got readings for voltages and continuity all across the motherboard, both from the dc input to resistors etc, and from the power button to resistors etc, i got readings for both voltage and continuity, and have tested repeatedly over a few days. There was just one issue i detected:
When probing voltage between the dc input jack on the laptop and the dc output jack on the motherboard, i see sparks when pressing the black tip against the output jacks pins and the mm readings jump all over. This happens each time on that component, making me hopeful i might only need a new dc jack and not a new motherboard.. Testing voltage and continuity from the dc jack on the motherboard to the rest of the motherboard yields stable readings however.

im not positive that i didnt skip testing some important component for voltage, but noticed no dead spots or area on the motherboard. Someone with a bit of experience who could give some feedback on what those sparks and jumping values on the multimeter mean? (again only between the dc jacks input and output)

thanks


Edit; should add that the laptop failed after the original adapter got fried from sparks at the receptacle. A new adapter didn’t solve the problem.

Edited by cumputer, 10 May 2018 - 04:27 PM.


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#2 Kilroy

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Posted 11 May 2018 - 04:35 PM

Testing for voltages, or lack thereof, is not of much use if you don't know what voltages you should be seeing.  For example, if something is shorted then when it is working properly you will see no voltage and when it is broken (shorted) you will see voltage.



#3 cumputer

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Posted 11 May 2018 - 09:48 PM

Nice. This lenovo flex 4 isnt that old, and i wasnt able to find a schematic for it on google, hence frankly dont know what voltage is to be expected from each component; i just went by what i watched in tutorials on other laptop boards, and also by the power supply voltage which is 20 V. Anyway, those cpl other boards in the tutorials mentioned. 19 V in, then reduced to and/or amplified to 2, 5 10 V etc across its MB components.


Will try with a new dc jack/cable and see, but if that wont work im not sure yet whether to get a used motherboard replacement or get a new laptop (would be my 2nd failed in a cpl short years, dont have a desire 2 even look for a new at this point). Any recommendations, as far as repair/s, replacement/s, or otherwise in this situation?

btw, i know motherboard replacement or getting a new laptop are the usual advice, but am looking at other potential possibilities atm.

Edited by cumputer, 11 May 2018 - 09:54 PM.


#4 cumputer

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Posted 17 May 2018 - 10:51 PM

hello?

#5 Platypus

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Posted 18 May 2018 - 12:35 AM

Will try with a new dc jack/cable and see


Anyone who has been following this topic will be waiting to see how this turns out.

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#6 mightywiz

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Posted 18 May 2018 - 01:30 PM

Testing for voltages, or lack thereof, is not of much use if you don't know what voltages you should be seeing.  For example, if something is shorted then when it is working properly you will see no voltage and when it is broken (shorted) you will see voltage.

your comment is incorrect!

If it's working properly you will see voltages, if it's shorted you will not see voltages or they may even be lower then what they should be.  but when a short happens and more current is being drawn then a fuse could blow and you won't see any voltages at all.

 

come on, if it is working properly then nothing should be shorted!

 

ok so your adapter with "no load" (means not plugged in) will always show a little higher voltage then what the adapter is rated at.  if you plug the adapter in and then read the voltages after you turn the computer on, you will get an accurate reading.  if your voltage (while plugged in) drops below 15v then you have an issue with either power adapter or computer.



#7 cumputer

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Posted 18 May 2018 - 02:50 PM

Great, and kinda what i suspected. My adapter is rated at 20 V, which is what i get with the multimeter give or take a little, going from the dc jack to various components on the motherboard, and lower voltages on some others. But the ones showing lower voltage values have shown it identically so far (i.e resistor shows 5 v, the other also shows 5).
Couldnt find a schematic for the flex 4s MB which could've made it more accurate.

Due to dc jack input to output on motherboard showing about 20 volt (though the value seems to jump depending on how hard i press the tip against the positive pins (red cable/s). Due to this id like to have a pro look at it, specially if i can find someone who charges a basic fee for diagnostics since ive no plan to let em replace anything (would feel slightly awkward for me to use em as a free service, unless its best buy, but if a few more fail 2 reply to my pretty short email question i just might), and that has good reviews).
And if they can tell me yes its the dc jack, or yes its the motherboard then ill order one myself, as well as install it).
Have contacted 2 so far, started by giving them a run dwn on what happened prior to this power failure hoping it'd help em pinpoint, but the first one didnt suggest any culprit, and am still waiting for a reply from the second, and will see if they find my description quote profitable enough to bother), otherwise ill be on my own and the web which is a slow process, but id like to learn little. Either way i wont spend $100s on a new notebook til ive exhausted these options. Ive asked actually 3 repair shop guys so far, the very 1st half panicked when i asked what could be wrong with the motherboard.

Edited by cumputer, 18 May 2018 - 10:56 PM.





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