Chosen Solution
I’m asking because I’ve never encountered these symptoms with any computer ever before. Symptoms: flickering power and Fn buttonslaptop screen blank I replaced the mainboard of my X270 with one bought from a Chinese store. I’ve done that before on other laptops of the same model and with different models. although no professional hardware technician, I’m familiar with that kind of work. I installed the replacement and booted up. The symptoms are as described above; the laptop screen is staying blank and the power and Fn buttons are flickering. Not blinking, flickering. This does not at all look like a post error blinking, it’s way too fast. The flickering might have a pattern that repeats after a pause, but that’s just a feeling and I first need to actually record the timings. With an external screen attached, the system can be used fine, but the flickering of the power button persists. It’s a very weird error. Do you have any clue about what could be broken and how does it cause the symptoms. Or are they unrelated? I’m baffled. p.s. I rechecked the flickering of the Power and Fn buttons; there is a pattern and it’s five flashes in about 0.5s, every 1s.
Hi @esarbe With the laptop turned on and no display, try shining a torch at an angle close to the screen and check for any images. They will be very faint so trying this in a darkened room may help to see them if they are there. If they are then then there’s a backlight problem with the screen. Since it is a new motherboard and assuming that the display is OK first check if the backlight power fuse F2 on the motherboard is OK and hasn’t blown for some reason. If the fuse is blown it is a 3A_32V_ERBRD3R00X fuse. The backlight power is fed to pins 13 and 14 of the LCD connector (video cable) There is always backlight power supplied to the screen and it is turned on and off in the screen by a signal voltage sent on the Backlight_On lead which appears on pin 23 of the LCD connector. This signal is controlled by the BIOS/OS and the backlights can be turned off for instance if the lid sensor detects if the lid is closed or if the OS goes into sleep mode etc. here’s an image form the schematic that may help with the backlights if that’s what it is.
(click on image to enlarge) Here’s the schematic for the motherboard (if it is a Lenovo X270 NM-B061 R04 board) that may help you further. I have no idea why the LEDs are flickering but if the laptop works OK other then the display of course, it may be a problem with the power supply that feeds the LEDs. Hopefully the schematic will help track it down. Hopefully a start.
