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How to bypass the hall effect sensor? (magnetic switch on monitor)?

T400/410/420 and T500/510/520 series specific matters only
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wrybread
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How to bypass the hall effect sensor? (magnetic switch on monitor)?

#1 Post by wrybread » Tue May 07, 2019 1:28 am

Well it's a long story, but the wire leading to the hall effect sensor on the left side of the monitor on my T530 got cut, and now it won't boot up. I think the motherboard thinks the lid is closed.

I stripped the wires down and there's 3 wires, one is ground and the other two are 3v. (black is ground, white and orange are positive).

I tried connecting the two 3v wires, no luck.

When I give it power (just AC adaptor, no battery) the power adaptor in the power light flashes green once and then there's no life.

I'm doing all testing without the battery plugged in.

I've gotten it to boot a couple of times, but just when I think I have it fixed it doesn't boot again.

Here's a nice explanation of how the hall effect sensors work on laptops:

https://www.youtube.com/watch?v=Fw0hA4RR2rU

What's strange is that according to the video the hall sensor sends 0v down one of those signal wires, which tells the mobo that the lid is closed. But both those wires have 3v, so I'm not sure what it could be.

I've done the obvious long hold the power button, and let it sit without power for awhile.

Any advice very invited!

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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#2 Post by RealBlackStuff » Tue May 07, 2019 3:46 am

Have you tried to disable "sleep when lid is closed" in the power settings?
Maybe the sensor-wiring is part of the webcam/mic cable?
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wrybread
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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#3 Post by wrybread » Tue May 07, 2019 4:11 am

The laptop won't boot. See that video if you'd like to learn about this sensor, it's a hardware thing, not software.

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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#4 Post by dr_st » Tue May 07, 2019 4:46 am

I have to question your fundamental assumption, since there is nothing that should prevent booting the machine even if the lid is closed. Consider looking for other failures.
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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#5 Post by RealBlackStuff » Tue May 07, 2019 5:09 am

I know how a HAL sensor works.
To fix it, you should replace the webcam cable 04W1714 https://www.ebay.com/itm/163240434982

wrybread
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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#6 Post by wrybread » Tue May 07, 2019 8:24 am

> I have to question your fundamental assumption, since there is nothing that should prevent booting the machine even if the lid is closed.

Sure there is. I have another T530, if I put a magnet over the hall effect sensor the machine won't boot. In other words pressing the power button has no effect.

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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#7 Post by Thinkpad4by3 » Tue May 07, 2019 10:40 am

wrybread wrote:
Tue May 07, 2019 8:24 am
> I have to question your fundamental assumption, since there is nothing that should prevent booting the machine even if the lid is closed.

Sure there is. I have another T530, if I put a magnet over the hall effect sensor the machine won't boot. In other words pressing the power button has no effect.
Yes, but I can name at least 5 things of the top of my head that could create the same effect with a different failure mode.
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wrybread
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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#8 Post by wrybread » Tue May 07, 2019 12:38 pm

I could name 50 things that would make a computer not boot, but as I said my issue started right after that wire was cut.

And as I said this laptop, like almost all laptops, won't boot with a faulty hall effect sensor (or the laptop in the closed position). And my missing sensor is most definitely faulty.

So anyway I'm still wondering if anyone has any ideas about bypassing it. I was considering connecting a transistor to the 3 wires, since I have plenty of transistors, but no spare hall effect sensor. And if I understand it correctly a hall effect sensor is a type of transistor. The three wires are black (ground), white (3.3v) and orange (3.3v), so I'm guessing orange is the signal wire. Just a guess at this point though.

Or some other idea?

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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#9 Post by Thinkpad4by3 » Tue May 07, 2019 1:28 pm

wrybread wrote:
Tue May 07, 2019 12:38 pm
I could name 50 things that would make a computer not boot, but as I said my issue started right after that wire was cut.

And as I said this laptop, like almost all laptops, won't boot with a faulty hall effect sensor (or the laptop in the closed position). And my missing sensor is most definitely faulty.

So anyway I'm still wondering if anyone has any ideas about bypassing it. I was considering connecting a transistor to the 3 wires, since I have plenty of transistors, but no spare hall effect sensor. And if I understand it correctly a hall effect sensor is a type of transistor. The three wires are black (ground), white (3.3v) and orange (3.3v), so I'm guessing orange is the signal wire. Just a guess at this point though.

Or some other idea?
Try using a dock to power it on. The dock power button should override the hall effect sensor, we'll at least I know it works on my T450.
Thinkpad4by3's Law of the Universe.

The efficiency of two screens equally sized with equal numbers if pixels are equal. The time spent by a 4:3 user complaining about 16:9 is proportional to the inefficiency working with a 16:9 display, therefore the amount of useful work extracted is equal.

wrybread
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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#10 Post by wrybread » Tue May 07, 2019 1:32 pm

Awesome idea, thanks. And of course it makes sense that the dock would bypass it. I think I have one at my shop.

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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#11 Post by dr_st » Tue May 07, 2019 2:59 pm

Interesting observations. Probably the lid closed signal disables the power button on the keyboard (maybe the entire keyboard). This explains why the power button has no effect, but of course once you turn it on via the dock, it should boot normally.
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wrybread
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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#12 Post by wrybread » Tue May 07, 2019 3:19 pm

Well shoot, my dock must be for a previous generation thinkpad, doesn't fit.

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Re: How to bypass the hall effect sensor? (magnetic switch on monitor)?

#13 Post by Thinkpad4by3 » Tue May 07, 2019 3:31 pm

wrybread wrote:
Tue May 07, 2019 3:19 pm
Well shoot, my dock must be for a previous generation thinkpad, doesn't fit.
There is a second method. Remove the keyboard and remove both the external battery pack and the internal CMOS battery and then plug into AC (he machine should fire up when it's plugged in
Thinkpad4by3's Law of the Universe.

The efficiency of two screens equally sized with equal numbers if pixels are equal. The time spent by a 4:3 user complaining about 16:9 is proportional to the inefficiency working with a 16:9 display, therefore the amount of useful work extracted is equal.

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