Dim screen fix results in bizarre keyboard behavior???

March 12, 2008 7:30 AM

We fixed an issue with a dim screen on a laptop, but now the keyboard is acting wonky. What's up with that?

The original problem with this laptop (HP Pavilion dv2035us) was that the screen was very dim. We've seen this often and generally this means that the backlight bulb has failed.

So we replace the backlight bulb on the LCD, but the problem is not resolved. So we go ahead and replace the entire LCD. Still the problem is not resolved.

So we try replacing the backlight inverter board. Still the same dim screen problem, now with a brand new LCD/backlight and inverter. Everything replaced and still the same problem, how can this be?

So we look into it further. The only thing we can come up with is the lid close switch. The switch that indicates to the machine when the lid gets closed and tells it to dim the screen and maybe go into sleep mode, etc.

We find the connector that is identified as the "lid close switch" a small cable that connects to the motherboard. We try to disconnect this connector.

The connector is made of plastic, but for whatever reason, the plastic on all of the connectors inside this laptop are very soft and almost what I would describe as mushy or spongy.

We try to gently remove the connector, but due to the mushy connection its sort of falls apart in the removal process. So we just cut the cable entirely.

Now we boot up and voila! the screen is no longer dim!

We put back the old LCD w/ new backlight and the old inverter board. System boots and the LCD is bright and crisp.

Everything seems well.

Then we find out the keyboard is not working properly anymore. The behavior is bizarre. Most of the letter keys work fine. But some of the functional keys exhibit strange results. The "delete" key when pressed with Notepad open outputs "b" and the Notepad Help window pop ups. The second time you press "delete" it then outputs "n=". The third time you press "delete" it doesn't output any text, but selects the Edit menu and turns Caps Lock on.

All of the functional keys on the final column of keys ("home" "pg up" "pg dn" "end") all exhibit similar bizarre behavior.

We can't figure it out, so we replace the keyboard with a brand new one. The problem does not go away...

So what is going on here? What would cause this kind of situation and what could possibly resolve it? This has to be a hardware issue, because connecting a USB keyboard to the laptop is not a problem. The USB keyboard does not have the weird issues that I have described. It seems to be a problem with the laptop's keyboard, but replacing it with a brand new one didn't fix it.

Anyone ever seen anything like this?? We are at a loss and need to restore the original functionality of this system. Any thoughts are appreciated!

posted by doomtop to Computers & Internet (1 answer total)

You cut or spliced some sort of cable connecting the internal keyboard to the MOBO. it'll be quite difficult to fix; normally i'd say better to just buy a new one off ebay, pull out the old one and plug in the new one. However, looks like you cut a secondary cable - i.e. kbd --cable1--> mobo chip 1 --cable2--> mobo chip 2 (cable 2 carried both kbd and monitor info - frequently ribbons in laptops carry a plethora of variegated signals to squish lots of things into a small space). If you can either fix the cut cable (solder it back together) or replace it, should fix the problem.
In the future, I'd advise against cutting cables in the computer without knowing exactly what you're doing - think pulling out a splinter and cutting an artery that got in the way. Bad idea.
posted by lrodman at 11:07 PM on March 24, 2008