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Old 03-27-2012, 02:19 AM
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Default How to disable this hall effect sensor?

This is one for all of you guys with more electronics background than I. I have a Gateway convertible tablet that I am trying to repair, the only problem is that there is a problem with the hall effect sensor on the MB that causes the back light to go out intermittently. Now, this is a shop use computer, so I really don't care if the backlight turns off when I close the lid. I have searched for a replacement sensor on digikey, mouser, etc, but can not find it. So I have decided to just remove it and bypass its function. Now, this is where my question comes in. I have found the switch on the board, I have measured the switch's behavior and figured out how it works. I think I have an idea on how to bypass it, but I just want to run this by someone who actually KNOWS and is not just guessing like me.

Here, I am referencing the numbered leads in the attached picture:

when back light is on:
Pin 1 has 3.66 volts, pin 2 also has 3.66 volts, and pin 3 is ground

which backlight off:
pin 1 has 3.66 volts, pin 2 has 0 volts, and pin 3 is ground.



So, it seems pretty obvious that pin 2 is the switched output. But, this being different from a regular switch I am a bit hesitant to just short out pins 1 and 2. Will this hurt something? What should I do to bypass this? just remove it? I'm sure this is obvious to someone, please enlighten me!
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Old 03-27-2012, 02:37 AM
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That looks like a transistor to me. If it were a hall sensor, you should be able to manipulate it with a magnet. Can you? Are you sure this unit even has a hall sensor? Most of them just use a micro switch near the hinges.

BTW, backlight going out randomly could also be a faulty inverter or loose LCD cable...
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Old 03-27-2012, 04:44 AM
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I am pretty sure it is not a transistor as the behavior changes when a magnetic field is introduced. Also, the magnet in the lid is EXACTLY over this component.
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Old 03-27-2012, 06:08 AM
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Quote:
Originally Posted by schwags View Post
I am pretty sure it is not a transistor as the behavior changes when a magnetic field is introduced. Also, the magnet in the lid is EXACTLY over this component.
Your correct, it is a hall sensor. That is why "SW7" (Switch 7) is printed on the MOBO.

You should be able to short pins 1 & 2 to complete the circuit without any problems. You *should* be able to leave the sensor attached, but the worst that will happen is that the Hall effect sensor will sink the 3.66v to ground, and not do anything... in which case you will need to remove the sensor and jump 1 & 2.
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Old 03-27-2012, 07:37 PM
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Thanks! That is exactly what I was looking for. I couldn't articulate the thought that the sensor might sink the voltage to ground, but that is what I was afraid of. I'll try it today and report back.
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Old 03-27-2012, 11:53 PM
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Update: I tried shorting pins 1 and 2, but no go. The back light now would not come on even if I put a magnet close and moved it around (it would flash as I did that in the past). I removed the short, and the previous behavior came back, so no damage done.
Then, I decided to just remove the whole thing (the sensor). Well, that didn't work either. Now again there is no back light at all. I measured the voltages, and between 1 and 3 is 3.66 volts, and between 2 and 3 is now 3.66 volts as well, but the back light is off!
So, I am not sure what to bridge or short or shunt or anything. Could the sensor have been providing some sort of necessary resistance between two (or three) of the connections? Could I replicate this with SMD resistors? I guess I could go hunting for a new hall effect sensor, but I could not find one with similar markings anywhere, and I do not know enough about the function of one of these to know if I am getting something compatible or not.
Any ideas?
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