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820-01521 no backlight after close/open lid

mbcontrol

mbcontrol

Member
I'm working on a 820-01521 (A1932) which had a liquid damage. I have repaired the board so that the machine is running now. I only have problem with the backlight after closing/opening the lid.

After opening it looks like the display is black. After pressing a Key the picture is coming up without backlight.
If i put it to sleep via the menu and then wake it up again, it behaves normally.

Can you tell me where to continue troubleshooting. If necessary, i can give you detailed information about the damage and the work i have done so far.
 
2informaticos

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

I bet for HAll sensor affected by liquid.
One is placed on the keyboard (left) and other on the audio board (right).
Check SMC_LID_LEFT/RIGHT levels.
Try known good audio flex/board.
 
mbcontrol

mbcontrol

Member
I changed the Audio board and Flex (known good, working in another A1932).
I also had to changed the keyboard (liquid damaged) to a new one.
And i changed the Flex left with Microfon and Hall (used from another MB).
Nothing was changed with this problem.
The microphone does not work either (with both Flex).

Then i measured ...
SMC_LID_LEFT = 1,59V
SMC_LID_RIGHT = 1,21V

SMC_LID_RIGHT had (only) 340Ohm to GND
SMC_LID_LEFT had 350kOhm to GN.
So I had a look to U4850, Pad 13 and 14 looked not so good, 13 was almost gone.
I fixed this and have now 350kOhm on both.

SMC_LID_LEFT = 1,59V
SMC_LID_RIGHT = 0,90V

Then i changed U4802, R4800 and R4801 from Donor - did not help.
I hope it have nothing to do with R4804 and R4805 near T2 or with T2 itself :-(

Do you have any idea what to do next?
 
2informaticos

2informaticos

Administrator
Staff member
SMC_LID_RIGHT isn't good.
Disconnect J6100 and check again.
Both signals should be high, when lid is open.
 
2informaticos

2informaticos

Administrator
Staff member
Trmove R4805 and check voltage at pin 1 of U4802.
If still low, check R4801.
You may also try to change U4802.
T2 is the last suspect...
 
Last edited:
mbcontrol

mbcontrol

Member
removed R4805 - U4802 Pin1 = 0,9V
new R4801 = 0,9V
change U4802 = 0,9V

What do you think? Is it an T2-Problem? What can i do next?

Or would it be an idea, making a bridge from U4802 Pin2 (LID_OPEN_LEFT) to Pin1 (LID_OPEN_RIGHT)?
 
2informaticos

2informaticos

Administrator
Staff member
Looks like T2 sinks too much current from that line.
You can try forcing the pull-up resistor, nothing to loose.
See what happens with 470K-100K resistor in place of R4801.
 
mbcontrol

mbcontrol

Member
R4801 with 392K = 0,934V
with 100K = 0,959V
Should I go down with the values from R4801? If so, how far? Is that uncritical?
 
Last edited:
mbcontrol

mbcontrol

Member
ok, i have no experience with t2 - what would you do?
Reflow or reballing? Or do you think the Chip is damaged?
 
mbcontrol

mbcontrol

Member
with 10k i get 1.173V
i would try to go more down with R4801
which value gives a safe high signal?

Arround U4802 is definitiv no corrosion.
R4805 is still from the board - so J6100 can not affect - is this right?
 
mbcontrol

mbcontrol

Member
Update - I installed the board for test:
mic is working now - think it was disabled because IPD_LID_OPEN was low
closing the lid have now no effect - don't go in sleep mode.

I think the customer can live with this and switch off over the menu before closing.

But could it be an idea to cut the trace to Pin1/U4802 and make a bridge to Pin2/U4802
So the machine would only use LID_OPEN_LEFT for this.

What do you think, could this work?
 
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