The ASUS X51R laptop exhibits a strange failure when its built-in CMOS battery is dead or low. Rather than having some kind of fall-back it basically ceases to operate from power-on. In some cases it will post a message about CMOS battery low but when you continue then it stays on a blank screen and doesn’t boot. Most of the time it will just power to a blank screen i.e. the laptop seems to startup and have fans and disk startup but no further POST or booting into the operating system. The “Zz” light may be on all the time but that is not relevant.
A client got this problem – one day it was booting fine and the next it was a blank screen so there is no early warning of impending failure.
The CMOS battery is a 3 Volt CR2032 style battery. These last for around 7 years so always keep them in their packaging so you can see the expiration date. Ideally use a new battery from a trustworthy supplier for a client laptop as it takes a long time to replace.
To change the CMOS battery you need to do a complete tear down of the laptop to the motherboard. There is nothing unusual with this teardown – if you have never stripped a laptop then this is not a job for you. I have done a lot so this was pretty trivial tear down,
– remove main battery, memory, hard disk, and WIFI
– remove all visible screws on bottom and back (they are all different sizes so draw a picture and keep them in separate piles),
– push in the 3-tabs at top edge of keyboard and lever out keyboard (unclip ribbon cable),
– lay screen fully back and lever up plastic covers on screen hinges and the curved plastic cover that is in the middle that is over the screen cables to motherboard plugs
– unclip the screen cables from the motherboard and flip over and unclip the WIFI cables and poke the wires out as you remove the screen (the screen itself just stays assembled to its hinges with 2x WIFI cables and 2x multi-way screen cables attached)
– unscrew the screws that you can see that were being hid by the keyboard and that were hidden by the screen that hold the top cover down
– unclip the narrow touchpad ribbon cable and pop up the top cover,
– unscrew the screws on the motherboard – there is a arrow-head symbol near each hole that marks which holes are used but ideally draw a picture and keep the screws seperate,
– unclip the fan assembly and cable, the speaker cable (towards middle front of motherboard) and battery feed ribbon cable and remove the DVD/CD drive if it’s not yet removed (it should slide out as its retaining screw is removed),
– carefully lift out the motherboard,
– you will see the battery on the bottom – it is a standard fitting – use a screwdriver to pop in the retaining tab and then remove and dispose – remember which way it was oriented but the +ve case side should be up (-ve small disk side down),
– do not use your fingers to touch your new battery but remove it from its packaging and clean your new battery with a clean dry cloth and then insert into the socket without touching it with bare hands. The reason to not touch it is that your hands have oil on them and over many years this can corrode.
– Re-assemble in reverse order.
Before re-assembling fan then please clean out the dust. There is nothing special to remember on re-assembly.
When assembled then it will boot instantly without any problems. The date and time will be wrong (reset to 2007 or similar) but you can easily reset this. With a new CMOS battery the laptop should last for another 5-7 years. The whole job takes about 1.5 hours.