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820-3662 Keyboard trackpad issue, was working, tried to fix backlight then issues

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Hellfiya

Member
I have an 820-3662 that was liquid damaged. I had to replace the keyboard IC because the V,B,N,M, , , keys were not working despite changing the keyboard. After changing the IC it was working but the keyboard backlight didn't work even though the system would let me turn it up or down. After taking voltage measurements it suddenly started working intermittently, sometimes it will flash on and off every few seconds but at the same time this occured the keyboard and trackpad stopped working when on. SMC reset works, the power button works to turn it on, and if i hold the power button down it turns off the mac. Could it be the trackpad cable? I didn't move it while testing the backlight voltages so it would be weird if that was the cause.

Also, this device had it's backlight circuit obliterated by the liquid damage, I replaced nearly everything on there and the backlight circuit is working fine now for display. Thunderbolt circuit was also destroyed, I removed most components on there and haven't decided to replace them yet.
 
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dukefawks

Administrator
I would suspect it is either a bad trackpad or a corroded trace to the connector.
Dont fix thunderbolt, it is hopeless.
 
H

Hellfiya

Member
Everything seems to be soldered in place correctly. The weird thing is I used the keyboard and trackpad perfectly for a month until I started poking around the Keyboard backlight circuit, I clearly messed something up. Maybe i was in resistance mode or something at some point. Keyboard backlight coil gets 5v on each side
 
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dukefawks

Administrator
Trackpad works without keyboard, but keyboard does not work without trackpad! Could be bad trackpad too then. Diode mode on all trackpad connector pins? Power to U4801 checked?
 
H

Hellfiya

Member
Trackpad connector diode readings

1-2 = ground= 0v
3-10 = OL
11 = .65v
12-16 = OL
17 = .643v
18 = .456v
19 = .643v
20-21 = OL
22 = .36v

I'm getting steady 3.3v on U 4801, which should make sense since keyboard power button and SMC reset work.

So as long as the diode mode readings appear ok, then I probably need to replace the trackpad.
 
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dukefawks

Administrator
pins 3-10 OL? That is of course wrong or are you measuring the trackpad cable? I mean the connector on the board.
 
H

Hellfiya

Member
I'm measuring the connector on the board in diode mode with black lead on the pins and red lead on ground, is that not the correct way? Or should I reverse polarity?
 
H

Hellfiya

Member
I only have some 2936 which have nearly the same circuit. the pins on the 2936 have much more .635v on more pins

I wonder if the 3662 needs part of the keyboard backlight for the keyboard and trackpad to work. It stopped working when I was doing tests on the keyboard backlight :/ Or maybe I shorted something on the tpad connector and messed up the pch.

I'm going to try a new trackpad and if that doesn't work then I'll likely sell this MacBook as is on eBay or something.
 
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dukefawks

Administrator
OL means there is no connection. If pins 3-10 all read open like that it is either a very dead U4801 or corroded traces. Also U4801 has firmware so you have to take it from a compatible board. Cannot take one from a 2936/3115 or something!
 
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