Question Dell laptop not working not booting

[bob12241]

Hi all
I am hoping that someone might help with a Dell laptop that is not powering up, I suspect the motherboard has gone but if someone could give me any further pointers I would really appreciate it. This laptop belongs to a cash strapped student, and I am trying to help him out. I have recovered some work files he was desperate for by connecting the HD to my desktop. The only peculiarity about this laptop is the keyboard has dual language on the keys, both- English alphabet and possibly Greek or Russian characters .
The laptop is made by Dell it has no stickers on the bottom except a service number, no OS sticker, no CPU stickers, so I can’t even give a model for it. It doesn’t power up and failed after a low battery shut down.
The symptoms are: press the power on button and the power Led lights for about 5 seconds then dies out, the fan isn’t turning nor does it even attempt to, no post (so no warning beeps), no splash screen, no perceptible backlight, no Leds except power( as mentioned above) and no drives winding up, in fact nothing.
I have individually unplugged and tried powering on each time after disconnecting the following : dvd/cd writer, hard drive (as said I have recovered some files for the owner he needed , on my desktop, so should rule that out), keyboard, memory (both sticks 1 at a time), wifi module, screen connector. I have tried various resets by removing power cord and battery as well as cmos battery. I have tested the power brick with voltage probes when disconnected ( not loaded though), but the Led remains lit when attempting a boot.

Regards Rob
PS. After searching the internet for the last 3 hours the Laptop appears to be an Inspiron 17-5758 i3

 

[lga1156_ftw]

What is motherboard model number? it can be anywhere on the motherboard, look this picture this is LA-5843P, REV 1.0. https://www.parts-people.com/index.php?action=item&id=20634
model number can be under sticker too.

Test that you get good voltage from the DC jack connector : https://www.amazon.com/Inspiron-037KW6-Harness-Connector-Socket/dp/B076118FFH
Black ones are ground and both red ones should have good voltage from other side of dc jack, you can try twitching the dc jack to see if voltage varies, if theres problem with it replace.

If it gives right voltage then disconnect internal monitor cable and try to boot ( be careful not to short anything when your doing this ) , if you get fan working then lcd is shorted or lcd connector cable.

You can also try remove CMOS battery (round coin battery) on the motherboard and try boot. Try also reset the cpu heatsink. Reseat RAM sticks, try with 1 stick only , if you remove both sticks you should get error beep or led flashiing.

 

[bob12241]

Hi thanks for your reply, it appears to be inspiron 17-5758 i3 processor judging by pics on internet , also battery fits for same model. Have tried memory previously, have tried cmos battery, not found pcb connections for jack as they are wired in and not pcb mount. One thing I have noticed is after being disconnected for 1 day, and then plugging in psu the power Led lights and stays lit for 20 or 30 minutes then goes off, when trying to power up the Led lights for about 5 seconds then goes out and about 20 seconds later it comes back on for a couple of seconds. Have also tried giving fan a whirl by hand at power up, no resistance or overrun seen. It is almost like the battery and psu aren't giving enough power to run and the led is lighting with residual battery power
Regards Rob