820-3476 no trackpad

Kyle93

Active member
Arrived with liquid damage. Replaced U4801 but still no trackpad or keyboard. Using known good keyboard and trackpad. Power button on keyboard works. Boots into OSX no problem.

Replaced U4801. diode mode on all pins of J4800 and J4813 is good. PP3V3_S4 is present. R4800 and R4808 are good as well.

what to check next?
 

2informaticos

Administrator
Staff member
KB/TP also not working before OSX?
Try to access boot menu for confirmation.

Did you try knwon good TP flex too?
Where was the liquid spill?

Post U4801 volatges before and after OSX login.
 

Kyle93

Active member
Yes KB/TP not working before OSX as well.

Using known good TP and flex.

Not sure where spill was. This is from someone who previously worked on and ultrasonic the board afterwards before arrival here. Liquid indicators red.

U4801 before OSX

pin 54 3.3v

pin 52 2.8v

pin 2 3.3v

pin 12 3.3v

pin 13 fluctuating between 0.400-.500v

pin 11 fluctuation between 400-500v


pin 24 1.6v

pin 10 1.7V

pin 9 .520v

pin 14 0v

pin 7 0v

will post after osx login voltages later
 

Kyle93

Active member
noticed pin 1 of J4800 3.4V without touchpad cable and with it its only 1.3V when it should be 1.56V

Bad J4800??
 

2informaticos

Administrator
Staff member
Aaaa, this is old style; always works in USB mode.
Don't bother to check voltages in OSX mode.

Pin 1/J4800 must be always 3.3V; w/ and w/o TP connected.
Looks like R4808 is bad in this case; replace it.
 

Kyle93

Active member
R4808 has been replaced. W/O TP connected 3.3V and without it its stuck at .793 V All traces look good.

What to try next?
 

Kyle93

Active member
Actually R4808 has been replaced several times on this board now. As soon as T/P is connected looks like it blows and has higher resistance.

T/P works fine on known working board
 

2informaticos

Administrator
Staff member
If resistor gets blown when connect trackpad, you have a short in that moment.
Is so dificil to check diode mode on that line, BEFORE applying power on the board???
Probably short appears between connector pins.
 

Kyle93

Active member
diode mode .388 pin 1 J4800 with and without trackpad and 3.3v with and without trackpad however as soon as screen is plugged in and OS starts to load drops to only .280V and R4808 blows.

jumper is ran from pin 1 of R4808 to pin1 of C3510 since PP3V3_S4 not present on R4808 otherwise.

Any ideas?
 

Kyle93

Active member
R4808 is no longer blowing up and no more shorts. Without t/p there is 3.3V on pin 1 of j4800 but once t/p is plugged in theres only 1.4V

A very small section of the board near C4808 is slightly popcorned. Could this have anything to do with the issue now? Anything else to try?
 

2informaticos

Administrator
Staff member
Looks like problem between copper layers board.
1.8V across R4808 should still blow it instantly; if is really 0 ohm.

Cut off PP3V3_TPAD_CONN close to J4800.
Remove R4808 and bypass from its pad 1 to pin 1/J4800.
Should be good to solder R4808 standing up on pad 1 and solder bypass wire on its other terminal.
 

Kyle93

Active member
After cutting PP3V3_TPAD_CONN and soldering R4808 directly on pin 1 to J4800 then running wire to other terminal still have same symptoms. 3.3V without t/p and 1.4v with t/p
 

2informaticos

Administrator
Staff member
If you disconnect the other end of TP cable, still the same?

R4808 didn't blow up, even with 1.8V across it?
It is really 0 ohm?
 
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