820-00239 works only with keyboard disconnected

Narek

Member
I have 820-00239 board which is working perfectly only with keyboard flex disconnected. Customer says, that computer was dropped. In most cases when I plug keyboard flex in (J4500) computer starts, shows Apple logo, loads system halfway and shuts down. Sometimes it lets me to write password, I can get to OS, but few seconds later it restarts. After disconnecting keyboard it works perfectly for hours. I took it to Apple, it got topcase and keyboard replaced but it hasn't solved problem. As there are fan power and data lines I've disconnected them from keyboard and tried without them - the same result. I've inspected board for damages, but haven't found any. It seems that keyboard flex causes problem on some communication line, but schematic doesn't help at all.

Diode mode readings of J4500 with everything disconnected from the board:

PP5V_S0_FAN_CONN - 0,431v
FAN_RT_TACH - OL
FAN_LT_TACH - OL
FAN_RT_PWM - 0,496v
FAN_LT_PWM - 0,496v
PP5V_S0_KBD - 0,430v
KBD_I2C_SDA - OL
KBD_INT_L - OL
KBD_I2C_SCL - OL
SMC_LSCO_RST_L - 0,707v (when board turned on gets 3,3v both with and without keyboard)
KBD_BLC_GSSCK - OL
KBD_BLC_GSSOUT - OL
KBD_BLC_GSLAT - OL
KBD_GLC_GSSIN - OL
KBD_GLC_XBLANK - OL
PP3V3_S4 - 0,315v

Diode mode readings of J4500 with keyboard connected:

PP5V_S0_FAN_CONN - 0,410v
FAN_RT_TACH - 0,406v
FAN_LT_TACH - 0,410v
FAN_RT_PWM - 0,496v
FAN_RT_PWM - 0,496v
PP5V_S0_KBD - 0,412v
KBD_I2C_SDA - 0,421v
KBD_INT_L - 0,550v
KBD_I2C_SCL - 0,554v
SMC_LSCO_RST_L - 0,434v
KBD_BLC_GSSCK - 0,676v
KBD_BLC_GSSOUT - 0,491v
KBD_BLC_GSLAT - 0,675v
KBD_GLC_GSSIN - 0,676v
KBD_GLC_XBLANK - 0,675v
PP3V3_S4 - 0,315v

I have also checked J4501, everything looks OK there. As I haven't found any chip on the board related to keyboard controll I understand, that it should be somewhere on keyboard itself, but I think it's not the problem here. The problem seems to be related to communication between board and keyboard, but I don't know where to look. Does SMC have any role here as there are comunication lines in connector?
 

2informaticos

Administrator
Staff member
SMC_LSOC_RST_L must be always high.
Check R5258, U5256 and traces.
Can also be a problem underneath keyboard connector.

SMC_ONOFF_L is steady 3V?
 

Narek

Member
SMC_LSOC_RST_L is always 3,3v, no matter with or without keyboard connected.
SMC_ONOFF_L steady 3,4v
All voltages on U5256 are present, only SMC_4FINGERS_RST is 0v

Keyboard connector is well soldered, on the other side of the boar there are only Q6000/Q6050 with some caps and resistos, they all look and measure good.
 

2informaticos

Administrator
Staff member
" SMC_LSCO_RST_L - 0,707v (when board turned on gets 3,3v both with and without keyboard)
----------------------
SMC_LSOC_RST_L is always 3,3v, no matter with or without keyboard connected"
Can you clarify, please???
Of course, interests this signal when board doesn't boot.
 

2informaticos

Administrator
Staff member
"only SMC_4FINGERS_RST is 0v"
Is correct; note that it doesn't have the "_L" on its name.

Keyboard data lines go to trackpad, J4500 -> J4501.
Only fans connect directly with the MLB.

Trackpad flex/board changed?
 
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Narek

Member
The whole topcase was replaced by Apple. I’ve asked them for details which parts they left there from old topcase and they have replaced everything except board, screws and Touch ID, so trackpad flex and board were replaced too.
 

Narek

Member
I’ve tried it, no changes. I connect only display and keyboard, board restarts while booting system. Even with everything connected to board except keyboard, it works perfectly. There are KBD_I2C_SDA and KBD_I2C_SCL lines in connector. I wonder, where are they going to/coming from? Between which parts is this communication going? Schematic is really poor with information about it, like they forgot to finish it.
 

2informaticos

Administrator
Staff member
Keyboard matrix information (key pressed) comes through I2C bus (J4500) and goes to trackpad (J4501).
Finaly, keyboard information goes to PCH via SPI, along with trackpad information.
 

Narek

Member
I see, thank you for explanation. I will check more carefully J4501 and inspect the areas under it. Also will check continuity of traces between J4500 and J4501. Would you dig into this board or it seems hopeless?
 

Narek

Member
I have checked continuity of traces between J4500 and J4501, they are OK. Also checked resistors and traces from J4501. I've reflowed SMC with no effect. I have no idea what else I can do.. Computer even can't be used with keyboard disconnected because it won't have working fans.
 

Narek

Member
Exactly, it was restarting all the time during boot. But today for example in most cases board doesn’t even try to start with keyboard connected.
 

2informaticos

Administrator
Staff member
Then the problem is not with keyboard matrix.
Should be something related with the fans, or keyboard backlight circuit.
Are you sure Apple changed all the mentioned things?
I don't understand why they changed all these things and returned machine as non working, really strange.

Just be sure SMC_LSOC_RST_L stays high.
 

Narek

Member
Are you sure Apple changed all the mentioned things?
I'm sure they have replaced complete topcase. Only things they left are motherboard, Touch ID, display and screws. They have replaced topcase under keyboard replacement program, but as computer already doesn't have warranty, they left it like that and said, that motherboard needs to be replaced too.

Should be something related with the fans, or keyboard backlight circuit.
I have disconnected both fans from keyboard and removed Q6000 and Q6050 - no changes. Will take a look at backlight circuit,

Just be sure SMC_LSOC_RST_L stays high.
It's always hight, 3,4v.
 
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Narek

Member
I started isolating pins in J4500 with capton tape and discovered, that when i isolate upper row of pins in connector, board boots fine. Then I isolated left/right half of pins, it turned out, that with right side of upper pins isolated board boots fine. I started isolating each pin separately and narrowed it down to KBD_I2C_SDA. With this pin isolated (no matter on J4500 or J4501) and both keyboard and trackpad flex connected board boots fine, but obviously keyboard doesn't work. With only keyboard flex connected board doesn't start at all.
 
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Narek

Member
@2informaticos, in meanwhile got the same mac model for repair with another issue and used occasion to swap the boards. This keboard with other board works fine. I put the board to another topcase with fully working keyboard and keyboard doesn't work. So the problemis related to mainboard itself..
 
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