[SOLVED]Another booting 820-4924 with no trackpad and keyboard

[bjf]

Corrosion on left part of keyboard connector and nowhere else. Testing with known-good functioning trackpad and keyboard.
• Boots normally
• Restored 3.42V on pin 4 of keyboard connector.
• I have no trackpad or keyboard.
• 3.3V on pin 27 and 12.6V on pin 1 of J4802.
• SMC_LID is at 3.3V. PP3V3_S4_TPAD is present - power to U4820 and U4830 is good. Everything matches up with a good board.
• Force touch click turns on when computer is turned on.
• Keyboard/trackpad do nothing in drive boot menu.

These are the exact same measurements as https://www.rossmanngroup.com/board...ing/13894-no-trackpad-or-keyboard-on-820-4924

Any ideas for what could be causing this? Apparently something is going on with this board when it gets hit by liquid in that area. Any help would be greatly appreciated. I'm really hoping to avoid starting a collection of booting 2015 Retina boards with no keyboard/trackpad.

 

[aprendiz]

PPVIN_S4_TPAD_FUSE present???

 

[bjf]

Yes, PPVIN_S4_TPAD_FUSE is good.

 

[aprendiz]

Did you replace the trackpad cable??

 

[bjf]

I'm actually not using that top case for testing. The one I'm using works perfectly with a working board.

 

[aprendiz]

Im out of ideas, lets wait Duke..

 

[dukefawks]

5V present on pin 25? Corroded pin on connector is likely just as much as that the cable on your test case has died. TP clicks once power is on?

 

[bjf]

Yes, 5V is on pin 25 of J4802. And yes, trackpad clicks as soon as the board gets power.

 

[dukefawks]

Inspect connector for corroded pins. Diode mode all the pins of the flat cable at the trackpad end to rule out a bad connector.

 

[bjf]

Connector looks flawless. I can put my good board in and the cables/trackpad/keyboard all work normally. This model has an odd system where the keyboard doesn't work without a trackpad present - unlike the old pros, and similar to the Airs except the keyboard doesn't run through the trackpad. I'm wondering if the interaction that allows the keyboard to work is somehow being hindered by something in the trackpad circuit.

 

[dukefawks]

Did you compare all pins on the connector on diode mode with a known good board? Best to do this at the flat cable on the TP side so you know the connector is good.

 

[bjf]

Good idea. It got me to recheck all of the diode measurements and I realized I missed TPAD_SPI_CS_CONN_L being slightly off (around 0.910 instead of 0.788). Led me to a bad Q4960. Board works fully now. Thanks.