820-4924 no keyboard

shlom

Member
hello

working on a 820-4924
board is very clean, no liquid damage..

keyboard does not work
tried it on a different case with good known keyboard \ trackpad and all good cables - still doesn't work..

with external keyboard works fine..

the keyboard does work when clicking the power button, smc reset
but does not work on pram reset or alt on boot for option menu...

i checked on j4813 and it has 3.42v on pin 4 and 3.3v on pin 30

any thoughts will be appreciated...

thanks..
 

shlom

Member
hi duke

thanks for the quick answer
i replaced the trackpad cable twice with two known good cables and no good...

also, put another logicboard into this shell and it works good, detects keyboard and works well
so it leads me to think that something is wrong with the board..

what can i check with it?
what the voltage should be on the rest of the connector pins?

thanks..
 

shlom

Member
hi

i just put this logicboard into a working machine, and did some more diagnosing..

the trackpad is clicking when the machine is powered on..

with the trackpad and keyboard connected i can't even use usb keyboard
BUT... when disconnecting the trackpad, i can get the usb keyboard to work
when connecting back the trackpad, the usb keyboard stop to work..

couldn't get the mac's keyboard to work...
 

shlom

Member
i got the logicboard alone, no OS or ssd

as i mentioned... with the trackpad connected nothing respond
not even usb keyboard, so even if i put an ssd with OS
i always get to the flashing question mark...

so i can't know if it moves..
i only get click when it's powers on...

will try to check again, try to get to recovery mode with the keyboard
to see if trackpad moves...

is there anything to diagnose or measure around
the board to try and figure this out?
 

2informaticos

Administrator
Staff member
Acces boot menu and see if trackpad works in that moment (before OSX charged).
At that time, trackpad talks with PCH through USB only...
 

shlom

Member
can't load boot menu

doesn't respond to alt key and also not to command+r

actually nothing response as long as the trackpad is connected
also no usb keyboard, so there is no way to know if trackpad moves..
 
Last edited:

2informaticos

Administrator
Staff member
Trackpad is connected to PCH through USB.
That is the way both talk before OSX is charged.
Seems that trackpad blocks the USB completely.
Check resistance to ground on both lines, when trackpad connected.
 
Last edited:

shlom

Member
i agree that it seems like trackpad is maybe causing short to ground
not by trackpad but on the logicboard...

where can i measure pch or usb while trackpad is connected \ disconnected?
 

shlom

Member
:|

i don't see a way to check when the trackpad is connected...
can you say on which pin of the trackpad to measure?
maybe on the boardview there is another point to check from?

i also have a 820-00138 board with almost the exact same issue
didn't thought would be such a nightmare to diagnose trackpad issues...

i literately have no clue where to begin from...
can't figure out the logic of it..

any directions will be appreciated..

thanks...
 

shlom

Member
hi

it's 11.5 k ohm on USB_TPAD_P
and 60k ohm on USB_TPAD_N

measure the same on a good board and it's the same..

the other side on this connection is the cpu so no way to measure when trackpad connected..

the PPVIN_S4_TPAD_FUSE is 12.56v is that normal?
on the schematic says 8.6v..
 

2informaticos

Administrator
Staff member
Mmmmh, cannot measure on the trackpad board???
Maybe easy to measure direct on the trackpad flex; on the terminal disconnected from logic board, with other terminal connected to trackpad...
Use ground from trackpad of course.

Bad values should be on trackpad side, if logic board values look good and it gets block only when trackpad is connected.
 

shlom

Member
hi
here all measurement on diode mode all pins of trackpad connector (red probe to ground)
o.l is ok on pins 1-13?

1 - o.l
2 - 0.000
3 - o.l
4 - 0.000
5 - o.l
6 - 0.000
7 - o.l
8 - 0.000
9 - o.l
10 - 0.000
11 - o.l
12 - 0.000
13 - o.l
14 - 0.000
15\17 - 0.000
16 - 0.000
19 - 0.746
20 - 0.676
21 - 0.629
22 - 0.711
23 - 0.632
24 - 0.000
25 - 0.535
26 - 0.480
27\29 - 0.332
28 - 0.430
30\32\34 - 0.000
31\33 - 0.000
35 - 0.391
36 - 0.429
37 - 0.389
38 - 0.676
39 - 0.000
40 - 0.000
41 - 0.619
42 - 0.460
43 - 0.578
44 - 0.435
45 - 0.592
46 - 0.754
47 - 0.000
48 - 0.461
 

dukefawks

Administrator
Looks ok. L4803 may be suspect. Measure voltage on both sides with trackpad connected so there is a load on it. Have you also inspected the connector for damaged pins?
 
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