Microsoft Surface Pro 4, Mobo: X911788-009 - Keyboard Not Working

Hello Everyone,
I am working on Surface Pro 4.
I have repaired the problem with charging circuit.
Tablet is working without any problems except detachable original keyboard.
Keyboard has been confirmed working on different machine.
My suspect was U3105 IC because signal enable from the chip to allow to produce 5V for the keyboard was missing:

Replaced the suspect but this has not changed anything.
Has Anyone had the same problem please ?
Thanking you in advance.
Regards,
Rafal

RafiManch napisal/-a:My suspect was U3105 IC because signal enable from the chip to allow to produce 5V for the keyboard

Hello!
The keyboard has nothing to do with the chip U3105, and it's also not connected to the 5V power rail.

- Plug an external USB keyboard and check if it works.
- Set your multimeter to the diode test mode and measure the voltage drops to ground on all pins of keyboard connector J3303 with the positive (red) probe connected to ground.

Hello Matic,
Thank you for your help. USB keyboard is working without any problems.
The problem is detachable original keyboard (confirmed working on different machine).
Keyboard is being connected to ports where 5V_KB is supplied to.
Is my understanding wrong please ?




Highlighted area is battery connector (on the right) and detachable keyboard connector (on the left):

Should I still measure values on J3303 (unpopulated connector) ?
Thank you.
Regards,
Rafal

Okay, so you are talking about the entire lower part of the machine, not the keyboard itself.
How about the TouchPad? Does it work?

Hi Matic,
No. TouchPad is not working either. It looks like enable signal for +5V_KB is not present. When I have traced it back U3105 should provide enable signal for the whole unit to be powered.

Measure the voltages to ground on pins 2, 3, 6 of transistor Q7401.

Hi Matic,
I have measured voltages as requested:
Transistor Q7401
pin 2 0V
pin 3 0V
pin 6 3.4V