[RESOLVED] (it was the CPU): Dead ThinkPad CPU?

[lezginka_kabardinka]

[RESOLVED] (it was the CPU)


Thanks to all for the input, I solved this by Occam's razor logic, and going by what a ThinkPad expert had told me, elsewhere (and what sounded counter-intuitive to me) - "Try the CPU first" - yep, it went pop like a blown light bulb; can you Adam and Eve it!

Got a ThinkPad L540, had it running for 9 months. The other day as I was using it, the screen froze and I held down the power to restart it... and BLACK SCREEN!

Have checked/tested:

~ LVDS (video ribbon cable to LCD) is fine
~ RAM modules are fine (have also tested with OTHER "known good" RAM from my main laptop)

It turns on, and if I remove RAM altogether, I get the (expected) 1-3-3-1 beep sequence which indicates "Hey! What's up? NO RAM?" etc. So it is doing SOME portion of the "POST" ("Power On Self-Test") sequence.

i5-4210m is the CPU, have ordered a spare one from eBay.


Any help (apart from "bake the motherboard in the oven to reflow" type comments) would be most graciously appreciated, thanks!

[lezginka_kabardinka]

No one at all?

[Peabody]

Is it possible it's just the display back-light burned out?  If you shine a flashlight on the display up close, can you see any indication that it's trying to display something?

Have you tried connecting an external monitor?

[lezginka_kabardinka]

Is it possible it's just the display back-light burned out?  If you shine a flashlight on the display up close, can you see any indication that it's trying to display something?

Have you tried connecting an external monitor?

~ No video detected (meant to mention that in initial post) - shone flashlight and another ring light, NADA.
~ No go with VGA out; tested on a TV and an external monitor.

Thanks

[jmelson]

Does it have a spinning hard drive?  If so, can you hear the drive seek during the boot sequence?  If so, it is likely a graphics issue, and could even be a software issue where the windowing system fails to start.  If SSD, then does the disk activity light flash?
Jon

[Halcyon]

It could be any number of things.

It's not impossible, but CPUs are extremely unlikely to fail. Aside from the days of the poorly designed AMD CPU's, I've never had a CPU just stop working in over 25 years.

In rough orders of most likely to less likely, I would suggest:

- Manifestation due to pre-existing damage (due to liquid or foreign matter ingress, exposure to extreme temperatures, mechanical damage...)
- Corrupt firmware (although Lenovo's self-healing BIOS should take care of this)
- Power supply or power regulation issue
- Problem with the GPU or display circuitry
- Fault with the motherboard or bad solder joint
- Fault with the CPU

[lezginka_kabardinka]

[RESOLVED] (it was the CPU)


Thanks to all for the input, I solved this by Occam's razor logic, and going by what a ThinkPad expert had told me, elsewhere (and what sounded counter-intuitive to me) - "Try the CPU first" - yep, it went pop like a blown light bulb; can you Adam and Eve it!