Power button lights up but the display is dead
I have a Lenovo ThinkPad T460 (board is BT462 NM-A581 Rev:3).
Whilst the laptop was powered on (plain web browsing, nothing fancy) Windows crashed with a blue screen of death. Subsequent attempts to start it failed. The CPU/Video Chip are from Intel (i7) and they come as a single package with 2 dies soldered onto the motherboard.
The behavior: the power button lights up (green), but that is about all the laptop does. There is no display (built-in panel or external monitor).
What I have tested:
- removed the board and visually inspected in —> all checks out. There are no visible faults
- removed all non-essential components (wireless card, disk drive) —> still the same problem
- removed the memory module —> when I power on the laptop I can hear 4 (3+1) beeps. So the chip is not dead because it does run the POST (to a certain point i believe).
- removed the heat sink —> when i power on the laptop I can feel the CPU die getting hot. So the CPU at least gets power
- checked power to the disk drive —> no power
- checked power to the fan —> the fan does receive power (5v) but it does not spin (the PWM pin is not energized)
Checking the Lenovo forums there are some users complaining about similar issues, but, unlike myself, they all have discrete graphics chips (usually Nvidia). But i have the built-in Intel chip. Some say that heating up the video chip will bring things back to live, albeit temporarily.
Besides heating up the CPU/GPU combo, do you have other ideas? Some things I could check or a reliable source where I can download the schematics (i do not mind to pay for schematics, but the sites I found online looked a bit dubious…).
Thanks in advance for the help!
Thank you so much for the help so far!
The schematics were exactly what i needed.
What is the status now:
- i have replaced the memory module and now the laptop starts (screen is on)
- however, POST still fails due to FAN failure. The FAN failure message comes on the screen and the the laptop shuts down.
The memory module is indeed faulty because I plugged it into another system and that failed as well to boot.
The fan _seems_ to be faulty. It uses a 5-pin connector:
- DC (in) —> 5v
- FAN Start (in)—> 5V
- FAN ID (out) —> no idea what this is about
- Tachometer (out)
I can confirm that during POST I have 5v on the DC in and FAN Start pin is pulled up (+5v). GND connection is ok too. However, the fan does not actually spin. The impeller is not stuck (it can easily rotate even if i blow on it with my mouth). I do not think i am capable of fixing the fan. The SMDs are absolutely tiny (majority of them are 0201) and (again) I was unable to find any schematics.
I am thinking of replacing it (approx $40) but then I cannot help thinking about how on earth it’s possible to have two components failing at the same time.
The laptop used to work just fine and it’s a personal device I had for years. One day I’ve started it, all was fine, but after some time all of a sudden it threw a BSOD and then never powered on. I can understand a failure of the memory module. I can understand a fan failure. But I find it very strange for 2 unconnected parts to fail at the same time.
It might be a bad coincidence, but I am also afraid of something else causing these failures.
Any advice/feedback is highly appreciated!