Laptop doesn't boot [Fan spin, no beep, no screen]

JCopse

Estimable
Oct 9, 2015
1
0
4,510
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Basic info:
HP DV7t-4000 (CTO, WV703AV base)

First occurred: A day or two after last opening it to clean. Shut down / power failure while watching a video on YouTube. Reboot attempt got me to the Win7 login screen, then the power failure happened again. Further reboot attempts resulted in fan spin up + wifi light + mute light (1 second or less) followed by power failure (fan spins down, all lights go out). No screen changes or sounds the entire time.

Diagnostic steps taken:
1) Purchased a replacement adapter from HP at their instruction, to make sure the problem wasn't the adapter. No change.
2) Used a multimeter to test voltage on both adapters. It was equal on both (roughly 19).
3) Used multimeter to test DC jack connection on laptop (result = roughly 17 between two of the connections, and less than that on other ones - but I was told that's normal). Guessed that the jack wasn't the problem.
4) Attempted a reset via removing the battery + adapter and holding down the power button for 30 seconds. No change.
5) Attempted booting with the battery taken out. No change.
6) Removed all components except for keyboard, attempted boot. No change.
7) Removed the CMOS/clock battery. Placed it back in after a few seconds. Plugged in one stick of ram (2gb) in one of the slots, connected speakers, and connected screen. Oddly, the fan spin was longer and a few of the hardware sounds I associate with booting up (clicks of some sort? no HDD/SSD was in, so I assume they're fan noises) occurred. Also, the subwoofer made a "pop" sound. Power failure happened before any screen change. Attempting another boot got a similar result. Attempting yet another boot resulted in the original "less than 1 second" fan spin and light flash, but kept the subwoofer pop.
8) Switched the ram to the other slot. Attempting to boot resulted in no change, except that now the subwoofer didn't make a "pop" noise.
9) Switched the ram again. No subwoofer "pop" noise, despite the setup being the same as the setup it had first occurred during.

So, in my mind the issue is clearly a power issue. I had at first thought it was the adapter, then the power jack, and then the motherboard. Now I'm not sure if it's the motherboard or the power jack, given the 17v reading I got and the odd behavior caused by unplugging and reconnecting various parts.

The part of the board I tested the power jack at is on the underside of the motherboard, below where it connects to the power jack. So, I'm not positive that the jack isn't the issue.


Thoughts on what the cause is likely to be?
 
Hi,

Pretty much you've done all the possible troubleshooting steps but I would suggest to try and connect an external monitor as well just to see if it's just a display problem and before concluding that it's the motherboard. If you're still getting indicator lights for wifi, hdd and power chances are it may just be the display.
 
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