820-3787 no trackpad no keyboard after liquid damage

Dozer

Member
hi friends.

I just have an 820-3787 here it had a hole in the board near u7100 and no power on

I replaced U7100 and soldered the missing traces. After that it worked, Trackpad working, keyboard wrote what it want. Then with a new Akku I noticed that It consumed 4-6A, after that I limited the curent to 3,5

I found that R7121/22 are bad. After replacing current was normal (about 3.4A not rising anymore)

Now I found that the damaged U7100 burned a hole in the Keyboard cable until the metal of the keyboard.

So I replaced the keyboard. But still the same problem.

I tryed another mainboard in the same case, now keyboard and trackpad is working well.


I dont know why but the keyboard and trackpad is not working anymore.

I found on J4800 Pin 22 and 18 has power,
Pin 20 Z2_CLKIN nothing

So I checked U 4801 and found in diode mode Pin 23-28 nothing.

I replaced U4801, Diode mode all pins ok now.J4800 Pin 20 has clock now. But no trackpad ( I disconnected the keyboard and only try to get trackpad until now)

then I found in the forum that duke wrote U4801 needs only power and usb and as to show up in the osx. I tryed with a good mainboard first. internal keyboard and trackpad is shown up.

with the problem board it shows nothing. In diode mode I get on R4801/02 both sides the same reading (good and bad board)

R4801 has 3.13V, R4802 0V. On the good board it has 0V as well

The U4801 is programmed. I took it from a 820-3332. Pinout is the same. may be there is no comunication?

External keyboard and mouse is working good

Need some help please
 

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Last edited:

2informaticos

Administrator
Staff member
First of all, get U4801 from donor board same model.
Could work, or not, from 3332; nobody can confirm that 100%, unless already tried that.
Be sure it receives correct VDD, pins 22/49.
Check if both R4801/02 are good.
Also confirm 0V at BUTTON_DISABLE signal.
 

Dozer

Member
R4801 has 24.6 Ohm
R4802 has 24.2 Ohm

means good I think.BUTTON_DISABLE signal has 0V
U4801 PIN 22/49 have 3.3V

I just have no donor here to test that, I have a good working board only. I will check that.
The Pinout is the same, I tryed the board with an mid 2012 retina trackpad but no way.
If there is a different then has the U1100 a problem in comunication with USB, but USB should be the same protocol.

For me is intresting that I have on R4802 0V also on the good board. I expected there signals like on R4801. Or is that because its differntial and no comunication, means one line has 3.13V, high pegel and the other has low pegel?
 

Dozer

Member
ok, when I look in the schematics, its 2 different things

U5701 (3332 board) and ___U4801 (3787 board)
CY8C24794_____________ CY8C24794
MLF____________________ MLF-1
(SYM-VER2) ____________(SYM-VER2)
337S2983 _______________337S4426

So I will look for a U4801 from same donor board
 
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