T520 lid sensor problems

[mitchW]

Hi,
I bought an used ThinkPad T520 that was supposed to be working w/o problems.
When I brought it home, the screen was dark and the keyboard wasn't responding. If I moved the screen up or down, the image came back for a second. No luck with returning it to seller, as he claimed that the laptop was 100% working when he was using it.

So, I took off the keyboard then and disconnected the LED/Camera/Lid Sensor cable. Now the laptop worked flawlessly, but of course I was missing all the disconnected stuff.

I then decided to buy another LED/Camera cable and replace it. Since I am from Europe, the only part that was reasonable priced was an used one, so I got that one. I then replaced it, and I was careful to route it exactly as it was before, etc.

The laptop worked flawlessly for 2-3 days, I reinstalled Windows, etc., but then I got random hibernate events, and the laptop stayed on for less than few seconds before it registered a close event and went into hibernate. I somehow managed to change lid close action to "none", but now I got screen that flickered every now and then. I put it to standby and after an hour when the laptop woke, I just had an black screen. I had to unplug the LED cable to get it back. I then tried the original (broken) cable and it seemed to be working fine, but that cable wasn't connected to camera or LED board.


TL:DR, now the question: are those cables both broken or damaged someway and are just a bad quality part, or am I having a problem with a logic board, or something completely different? Disconnecting the cables always made the problem go away.

[kfzhu1229]

The lid sensor is a small board with a transistor mounted on the left side of the screen bezel for every T510-T530.
Perhaps first try taking off the screen bezel and see if anything improves?
Then try putting a piece of magnet close to it and away from it, it should respond to lid close and open exactly as you move your magnet.
Also, unplug, clean (with contact cleaner) and reseat the screen cable. The screen cable carries a lot of current and can get oxidised as well.
UNPLUG the battery and charger when you do that. the cable carries 10-19V even if the computer is off!

[mitchW]

Hi, yes the hall sensor is a 3 pin SMD device mounted on a small PCB on the left side of the LCD.
Taking off the bezel didn't seem to help in any way.

If I bring the magnet close to it, it turns off the LCD.

The connector was cleaned with professional contact cleaner as well with a fibreglass brush.


Should I order a new unused cable or is there a chance that is something wrong on a mainboard?

[mitchW]

I got the schematics for this logic board, and I measured pin 7 on the LED/Camera connector which is LID/SENSE pin.

It is being held to a 3.3V, but when the screen flickers, the voltage briefly dips to 2.7V.

Anyways, I ordered a brand new cable and we will see if this solves my problem

[kfzhu1229]

Well I suppose a cheap way to fix is just wire the pin directly to 3.3V power supply on the board. It will make the lid sensor not work anymore but hey I think it's a small tradeoff to make.

[mitchW]

Hi,
I got the new cable from China. Looked unused original part.
Not even 5 minutes after I replaced it, I got now famous black screen. The LID_SWITCH voltage was again stuck at 0V. Bringing a magnet near the sensor sometimes made it to turn on for a moment.

I disassembled the whole bottom part, took the motherboard out, washed it with a strong household cleaner and deionised water. After drying in an oven for 2 hours at 95 deg. C, I put it back. Of course still no change. For anyone who think that the cleaning mainboard with water would be bad, I do have a lot of experience with that and I had luck with the boards that were used in some very filthy environments (grime made some leakage paths on the PCB).

I tried pulling up the voltage with a lower resistor value (factory is pulled with 100K to 3.3V). I just paralleled lower value resistors and connected them to the same 3.3V source, but even at 4.7K there was still no change, the LID_SWITCH still stayed at a low level, albeit higher than usual.

I also tried connecting a 0.1-0.47uF capacitors from that pin to ground, as perhaps there could be some oscillations or ripple. No change.

Last thing I did, was to remove the wire that carried LID_SWITCH to the hall sensor. Now, finally (of course), I get image but the lid switch wont work.
So, my thoughts are:
- the EM-6781 hall sensor IC on the cable itself is dying after 8-9 years, so all of them I got are bad
- I have some ripple on the VCC supply line to that IC causing it to act up sometimes (remembered this just moments ago)

Any comments welcome

[kfzhu1229]

I disassembled the whole bottom part, took the motherboard out, washed it with a strong household cleaner and deionised water. After drying in an oven for 2 hours at 95 deg. C, I put it back. Of course still no change. For anyone who think that the cleaning mainboard with water would be bad, I do have a lot of experience with that and I had luck with the boards that were used in some very filthy environments (grime made some leakage paths on the PCB).

Washing the motherboard is definitely not bad as long as you dry it properlyt, but 95C of drying temperature is way too high in my opinion. Maybe 50C is like the max I would put it at. Leave it on top of the furnace for example will do.

I tried pulling up the voltage with a lower resistor value (factory is pulled with 100K to 3.3V). I just paralleled lower value resistors and connected them to the same 3.3V source, but even at 4.7K there was still no change, the LID_SWITCH still stayed at a low level, albeit higher than usual.

I also tried connecting a 0.1-0.47uF capacitors from that pin to ground, as perhaps there could be some oscillations or ripple. No change.

Last thing I did, was to remove the wire that carried LID_SWITCH to the hall sensor. Now, finally (of course), I get image but the lid switch wont work.
So, my thoughts are:
- the EM-6781 hall sensor IC on the cable itself is dying after 8-9 years, so all of them I got are bad
- I have some ripple on the VCC supply line to that IC causing it to act up sometimes (remembered this just moments ago)

Any comments welcome

Hmm have you checked by any chance that your LCD itself might have magnets mounted onto it? I have seen old MSI laptops doing that and if you replace the screen with one of those without taking care of the magnets yeah that might be a problem. Like remove the LCD from the lid perhaps and see if the issue persists.
Have you also tried to pull the pin up to 3.3V directly and see what gets hot? Maybe that tells you what is shorting to give you the lid sensor issues.

[mitchW]

Managed to repair it by wiring the 3.3V directly to the signal...