[Macbook pro A1708] [Boot loop] [Trackpad ?]

[No Lan]

Hey everyone,

Usually, I'm not the type to ask for help, but this time, I'm calling on your wisdom and expertise I've seen what this community can do, so I'm pretty sure you guys can help me out.

Here's the deal: I noticed my MacBook got stuck in a boot loop. After opening it up and doing some initial troubleshooting, I found that the boot loop stops only when the trackpad is unplugged.

Now, just so you know, the trackpad actually works — I tested it with another motherboard and it's all good. Same for the cable, no issues there. The problem is only with this motherboard (820-00840).

Another weird thing I noticed: when the trackpad is plugged in, the fan doesn't spin. But when it's unplugged, the fan runs just fine.

I checked with L4800 and C4800, no shorts. Also got 5V on PP5V_S4_TPAD_CONN.

Honestly, I'm a bit stuck on what to do next to find the root cause.

Oh, and important to mention: I did something I probably shouldn't have, but I wanted to test it out — I waited for the Mac to boot without the trackpad, then plugged the trackpad in hot.

It worked for about 20 seconds before it rebooted again.

So yeah, that's the situation! Looking forward to your bright ideas! Thanks a ton

[mon2]

Review the voltage to ground of the I2C lines on the trackpad connector. These are SCL / SDA.

[No Lan]

Thanks you for your reply

I found these 2 lines on the boardview for J4801 TRACKPAD

SMBUS_SMC_3_S0_SCL --> 3.3V
SMBUS_SMC_3_S0_SDA --> 3.3V

Do i need to make furher test on it ?

[mon2]

Also, pins 8 and 12.

Post the voltage measurements to ground of each TPAD_*** signal.

[No Lan]

Okey,

just to be sure, i'm taking measurement without Keyboard and trackpad connect. Is that good ?

KBD_I2C_SDA --> just after connect USB-C it slowly going from 0 to 1,50v-1,84v --> not stable
KBD_I2C_SCL --> just after connect USB-C it slowly going from 0 to 1,50v-1,84v --> not stable

TPAD_SPI_INT_L --> 3,29v
TPAD_SPI_MOSI --> 0v
TPAD_SPI_CS_CONN_L --> 3,33v
TPAD_SPI_MISO --> 0v
TPAD_SPI_IF_EN --> 3,33v
TPAD_SPI_CLK --> 0v
TPAD_VIBE_L --> 0v

i also noticed something strange. On PP5V_S4 (L4800) i measured 8-9v and sometimes strictly 5v

Sometimes the Mac boot with trackpad sometimes bootloop..

[No Lan]

Just because I measure 9V on PP5V_S4 one times, should I be concerned that U7650 might be malfunctioning sometimes? Or is it not handling the voltage as expected?

[mon2]

What is the current draw for this logic board? Are you at a stable 20v? If not stable 20v, review the article on the internet for the 'CD3215 and 20v'.

[No Lan]

I'm fully stable 20v and between 0,4 and 0,8A without batterie connected.

[mon2]

Do you ever see the Apple logo or hear the boot chime in any of these attempts?

What is the voltage to ground of PPBUS_G3H? ALL_SYS_PWRGD?

[No Lan]

Just to clarify

if trackpad is disconnected --> Mac boot with fan --> Logo Apple --> Screen for user authentication --> Stable
If trackpad is connected --> Mac boot without fan (fan work only for few second) --> Logo Apple --> Boot loop OR Mac boot without fan (fan work only for few second) --> Logo Apple --> Screen for user authentication crash and restart

for your question

PPBUS_G3H--> 13,2v
ALL_SYS_PWRGD --> 3,23v

[mon2]

What is the motherboard that works with this same trackpad with the same cable? Is it the 820-00840?

[No Lan]

Yes it is the exact same motherboard 820-00840

[mon2]

With the trackpad disconnected, you should have a high fan spin since the (trackpad) thermal sensors are not being detected. Is this correct? You can review the other working board for the expected high fan spin condition.

[No Lan]

I agree with you.
with the 2 motherboard (the one for this post and the other working well) i have a high fan speed when trackpad disconnected !

[mon2]

Boot into SAFEMODE with the trackpad connected.

To start an A1708 MacBook Pro in safe mode, you need to restart the computer and press and hold the Shift key until the login window appears. Once logged in, you can verify safe mode by checking the System Information app.

Does this trackpad with the same cable function with this (non-working) logic board?

Review the mating connectors for possible dry solder or lifted pin on the SMD joints.

[No Lan]

I cannot connect as the system keep restarting before or during login windows :/
even when starting in safe mode

[mon2]

Remove all power. Meter in resistance mode. Mate the trackpad to this board.

Measure the resistance to ground of:

PP5V_S0_FAN
FAN_LT_PWM
FAN_LT_TACH

[No Lan]

Here the result

PP5V_S0_FAN --> 1,8
FAN_LT_PWM --> OL
FAN_LT_TACH -->OL

[mon2]

What are the units of measurement?

PP5V_S0_FAN --> 1,8

1R8 ohms to ground?

[No Lan]

Sorry i was in diode mode.

Multimeter on 2000K ohms and i observe between 220 and 240 on PP5V_S0_FAN. took on C4870

FAN_LT_PWM --> OL
FAN_LT_TACH -->OL