Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

[fred23456]

Hi there,

Working on a water damaged Macbook Air 820-3437.
The fan ramps up to 100% on boot and stays that way, I believe the sensor causing this is the touchpad palm sensor as all the others read usual values, aside from this one which reads nothing.

I checked the touchpad flex, it was corroded so I replaced it with no change in behaviour. I then removed and re-soldered the touchpad connector on the logic board (also corroded inside). This also did not fix the problem. I swapped the touchpad for a replacement and still have the issue. I've tried the unplug the webcam cable trick to see if it's a sensor on that line and that does nothing too.

The computer now boots into the "Trouble entering your password screen" as if to suggest the keyboard isn't connected.

Really racking my brain with this one and worried it may be an SMC problem?

Any help would be much appreciated!

[fred23456]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

Just an update to this, the mac now boots into the OS. I blew a little air into the keyboard/touchpad connector on the logic board and must've cleared out something. The keyboard and touchpad are working properly now.

The fan is still spinning at 100% and the computer is running a bit slower than usual.

[piernov]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

Run ASD to find out which sensor is causing the issue.

[fred23456]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

Hi there, sorry for the delay in responding. Managed to find and setup ASD.

Failed tests are as follows:

Ts0P Trackpad Skin - reading below the low limit.

[piernov]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

Yeah so it's indeed related to touchpad. Either bad touchpad, bad cable or and issue with the connector on the logic board still. I think the sensor readings go through the SMBUS (pin 16/17) so you may want to pay extra attention to those lines.

[fred23456]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

As mentioned previously, I've switched around 2 touchpads, tried 2 new flexes and have soldered 2 new connectors onto the board and the issue remains the same whilst other problems with the keyboard/touchpad disappeared.

As far as I can tell from the schematic the data line from the touchpad connector goes straight to the SMC on this board? Would really appreciate if you could verify whether I'm right or not.

[piernov]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

U5810 is on the same SMBUS than the touchpad, so if there was an issue with the SMC or the bus itself I'd expect you to have more than one sensor issue (assuming you did "continue on error" in ASD).
The SMBUS connection is indeed direct between touchpad connector and SMC (and U5810).

You could check if you have continuity between the touchpad connector and U5810 for the SMBUS lines just to make sure there's no break in the SMBUS lines near the touchpad connector.

[fred23456]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

I did indeed continue on error in ASD. The touchpad is definitely the only sensor that's wrong.

I have 3.3 volts on SMBUS at U5810 on pins 9 and 10 and on R5390 and R5391. Pin 16 (SMBUS_SMC_3_SDA) of the connector is also 3.3V but pin 17 (SMBUS_SMC_3_SCL) is 0.4V

I can't get continuity on SCL to U5810. Easily get it resting the probe on U5810 pin 9 and running it across the connector but nothing on pin 10. Is it time to start running jumper wires?

[piernov]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

Yeah if SCL is not good on the connector but is good at U5810, there's a break in the line somewhere. Check under microscope if the pin is not soldered or the pad is gone, and see if you can find a via to solder to. Otherwise you'll have to run a jumper wire across the board to the other side.

[fred23456]

Re: Macbook Air 820-3437 - Fan 100% and Magic Mouse Screen on Boot

Ran the jumper loosely round the board to test and the fan spin is back to normal! Going to get some solder mask to make sure it's insulated and doesn't cause any other issues. It's a bit of a journey it has to take round the board! I'll give ASD another run and check whether the sensor passes once I've got the wire routed properly.

Cannot thank you enough for your help! You've helped save my computer from what I thought was certain death.

-EDIT-

Tested with ASD after routing the jumper properly. Ts0P reading properly. Boots to the OS, everything working as it should. Thanks again Piernov!