Member Avatar for bigfroggmann

Hello.
I have a presario 700z ,the machine boots fine I think, what I mean is I hear it but I don't see it..I swapped out a working good screen and still same problem.. is there a video chip somwhere or is the whole mother board fried??
TIA

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Quick summary: the problem turned out not to be the LCD itself but the lid/cover switch — thanks to for pointing it out and to for confirming the fix. Several people suggested panel, cable and backlight checks; those are valid checks but the lid switch can quietly force the internal display off while the system boots and an external monitor still works.

How the lid switch behaves and why it can be confusing: the switch tells the firmware/OS the lid state and typically disables the inverter/backlight or the panel when it reports “closed.” Laptops use either a tiny mechanical microswitch or a magnetic/reed sensor mounted near the hinge or bezel. Typical failures are stuck plungers, cracked plastic that misaligns the actuator, or a failed reed/microswitch so the system always sees the lid as closed.

Practical, safe troubleshooting steps to verify the switch (without repeating earlier checks): power down, remove AC and battery, then access the bezel area to locate the small switch or its cable. With the connector unplugged, use a multimeter (continuity or low ohms) while actuating the switch — a healthy switch changes state when pressed. If it’s a magnetic type, hovering a small magnet over the sensor should change the reading. Do not short unrelated pins; observe ESD precautions and stop if unsure.

If the switch is bad, replacement parts are inexpensive and often sold as a bezel/top-case subassembly or a small switch module. Inspect hinge alignment and the bezel for broken plastic that could prevent proper actuation. If not comfortable disassembling laptops, a local technician can confirm and replace the part quickly.

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Member Avatar for bigfroggmann

did I mention it does work with a monitor plugged into it...anyone??
;)

Member Avatar for JANINE

could be a chip failiure but doubtful as you've stated that the machine works if you hook up an external monitor.


it could be a backlight has gone (tell this be shining a bright torch onto the screen and seeing if theres outlines of a dialogue box etc)

it could also be that the thin flat wire that goes from the board into the screen has become damaged or isn't plugged in right. be careful if doing it yourself and to be frank i'd get a professional to look at it for you.

Member Avatar for bigfroggmann

Thanks Janey, but Like I said I switched with a known working on, also put the one in question on a working machine ..works fine..I also switched all the small cables running to motherboard..and that's what confuses me the most is that the unit works great when plugged into an external monitor ......any other suggestions??

Member Avatar for BuggZ

Check the BIOS settings to make sure the LCD is enabled. Also try the Fn key combination to switch from LCD to external display (might be a combination like Fn + F5 or Fn + F8). If it still doesn't work, check the LCD close switch to make sure it is functioning.

Member Avatar for bigfroggmann

HEY buggz !!! you the man!!! It was the lid switch....I knew I could get help here..I don't know much about laptops, but I'm learning all the liitle tricks from all the knowledgable peeps here...thanks all that helped :cool:

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