[RESOLVED: CPU had died!]: ThinkPad L540 froze then rebooted and now black screen

[glossywhite]

[RESOLVED: CPU had died, was replaced and it is now A-Okay!]


Hello everybody. My ThinkPad L540 (20AV-0070UK) suddenly froze in the OS, and then (I think, but can’t be sure as I was stressed at this) rebooted… or maybe I held power down.

The upshot of it is that I’ve conducted every conceivable combo of main batt/bios batt/charger removed, holding power button down for 30 seconds and also one minute, with all power, sources removed, the same with ram removed and the bios battery removed. Nada

I tried the 9 power button brief presses then the 10th power button press for 30s, with ram, bios battery, main battery and PSU unplugged … then plugged in psu with no ram installed, pressed power and got the 1-3-3-1 ram beeps, so clearly BIOS is working.

Measured old BIOS battery @ 2.6V, so clearly too low. Temporary fix is that I peeled off the welded tags and kept them attached to the lead/plug and have temporarily taped them to a good battery (CR2025)


Nada. Fans come on, machine comes on, display is black. Tried all the above with Ssd removed too.

Help me please! Thank you so much. God bless you.

[glossywhite]

I know you’re busy people, and there may be a delay between time zones etc; if anyone is able to suggest a few things I can try, I’m really up the creek right now. I hope this isn’t seen as demanding, I’ve just got to get my work done and my data back. Thanks all

[axur-delmeria]

Try powering it up without any RAM and HDD/SSD attached (disconnect the charger and batteries beforehand). I expect to hear some kind or error beep code which indicates that the BIOS/UEFI still goes through POST (power on self test), though to be completely honest I haven't tried this on Thinkpads newer than my X220 so I can't verify that your L540 will behave the same.

If it does sound an error beep code, that means there's still hope. Power down, disconnect charger and batteries, then install 1 stick of RAM. Power up, expect it to boot. If it doesn't, remove the RAM stick and install the other RAM stick (I'm assuming you have two installed).

[glossywhite]

Try powering it up without any RAM and HDD/SSD attached (disconnect the charger and batteries beforehand). I expect to hear some kind or error beep code which indicates that the BIOS/UEFI still goes through POST (power on self test), though to be completely honest I haven't tried this on Thinkpads newer than my X220 so I can't verify that your L540 will behave the same.

If it does sound an error beep code, that means there's still hope. Power down, disconnect charger and batteries, then install 1 stick of RAM. Power up, expect it to boot. If it doesn't, remove the RAM stick and install the other RAM stick (I'm assuming you have two installed).

Thank you.

Yeah it’s still POST-ing as I followed the same deductive logic as you suggested, and get the 1-3-3-1 RAM beep code with no RAM. I tried putting one stick in alternate slots with the other empty - beep code went away but it doesn’t boot.

[glossywhite]

Update:

I did all that and there’s no error beeps but there’s still a black screen and no booting.

No sign of ANYTHING on the LCD, even with two bright LED flashlights aimed at the LCD from a shallow angle. Nada.

Update 2 (possible brainwave ):

I had a thought; since POST seems to be happening, but neither video nor backlight are on the display, maybe it’s a loose LVDS cable?

[RealBlackStuff]

Tried an external monitor?

[glossywhite]

Tried an external monitor?

I don’t have one, nor do I have the right cable. No money either.

[glossywhite]

Is it possible that a poorly seated display ribbon could cause a machine to freeze, and also to show no video and backlight? The service manual mentions reseating said cable for no backlight issues.

[RealBlackStuff]

Make sure to remove charger and batteries before you try to reseat it.

[glossywhite]

Yep. Done all this now. No dice.

[glossywhite]

Is it common (or likely) for the ACTUAL LCD PANEL to "blow"? I read somewhere this can happen; seems improbable. I am currently pootling along on my old backup machine, an HP ProBook 6460b - it sounds like a jet engine and is VERY grainy!

[glossywhite]

A friend is dropping off a VGA cable today (Weds 13th GMT) and I shall see what's what. If that works, and I see output, I shall be looking at the LED backlight fuse and trying to bridge or replace it. This is life eh; inconvenient, but I count my blessings - I am happy and healthy - what a luxury to live in a society where we HAVE the choice of a "spare laptop"!

[glossywhite]

UPDATE:

Tested with brand new VGA cable + LCD 1366x768 monitor (an LG "W1946"):

~~ Sanity check; tested monitor on my HP ProBook 6460b, works perfectly.

~~ L540 test: No signal, tried FN+F7 with "Function Lock" ON, OFF and otherwise. I also tested it using CRTL+F7 with "Function Lock" ON, OFF and otherwise (because in BIOS I'd swapped CRTL+FN, even though by now BIOS is prob reset, I did it to eliminate it)

NO SIGNAL! NADA!

Would the VGA output signal drop down automatically on boot, to match the 1366x768? (and what res does the L540 put out, at boot, via VGA?)

Thanks!

[glossywhite]

Based on this post: https://forum.thinkpads.com/viewtopic.p ... 43#p811083

… it appears my CPU could’ve fried itself; ideas?

[RealBlackStuff]

Replace the (socketed) CPU with one of these:
i5-4200M
i5-4210M
i5-4300M
i5-4330M
i7-4600M
i7-4702MQ (I have this in my T440p)
i7-4712MQ
HMM here: https://download.lenovo.com/ibmdl/pub/p ... 004_03.pdf

[glossywhite]

Replace the (socketed) CPU with one of these:
i5-4200M
i5-4210M
i5-4300M
i5-4330M
i7-4600M
i7-4702MQ (I have this in my T440p)
i7-4712MQ
HMM here: https://download.lenovo.com/ibmdl/pub/p ... 004_03.pdf

That’s fantastic, thank you. How do I know conclusively that it is the CPU at fault?

[RealBlackStuff]

You won't know till you tried it.

[glossywhite]

You won't know till you tried it.

And would a dead CPU prevent the backlight from coming on too?

[RealBlackStuff]

Yup.

[glossywhite]

Have ordered a used i5-4210m + some grease. Will report back. I’m extremely grateful for your help and patience. God bless you.

[glossywhite]

As per edited opening post, the issue is now resolved, and a huge thanks to all. A mere £8 used i5-4210m on eBay, and I resolved a dead CPU error (which, although is apparently uncommon, it is now clear CAN happen).

Thanks everyone