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2020 A2338 Trackpad And DFU Issue

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PaulPCGuy

Member
Hello, I feel like this is probably an obvious fix but I'm just not getting it. I have a 2020 A2338 (M1) that I replaced the panel on. I was going to go through my checklist, but was stopped by the keyboard and trackpad both being unresponsive. I swear I remember this working at some point, but I'm not positive. Regardless, the touchbar does work, and external peripherals do work.

MRI reports the trackpad is not detected, and that is also reflected on the setup screen where it has the prompt to connect a mouse/keyboard.


I didn't see any issues on the board or the trackpad, so I tried a DFU restore. It errored out with -1 (no trackpad) so I replaced the cable with a new one and got the same error. I replaced the trackpad with a known working donor from another M1 A2338 and still the same error. I do want to note that the keyboard is active during preboot, as it is able to recognize the DFU key combination. And on the topic of DFU, this MacBook seems to be either ignoring or heavily delaying its responses to VDMs sent by MacVDMTool. I say this because if I send the DFU message, it will not react however will immediately enter DFU if I manually shut it down shortly after sending the message. Same deal with reboot. Considering USB devices work on both ports, and both ports are able to charge, I'm hesitant to call a port problem.

Again, I didn't see any issues on the board, and I'm not sure what is required for the trackpad to be detected.
 
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PaulPCGuy

Member
Neither have voltage present. I tested minimally - board, trackpad, connector. No fan/battery/etc. Additionally, I noticed that the entire PP1V8_AON line only goes up to 0.062V, which is odd because it does get 20V, does boot, and all the other rails are present. I thought PP1V8 was essential for booting but I guess not?
 
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PaulPCGuy

Member
PP3V8 and PP1V8_EN are both present. Since there's nothing else connected to this except GND and PP1V8, I assumed UC120 went bad. Put a donor on from a board that has 1.8V and still no voltage. Weird. I'm going to inject into the rail to see if there might be a short my meter didn't pick up. If there isn't, I guess just keep trying new ones?
 
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PaulPCGuy

Member
I tried a DFU restore with the same configuration as before, but injecting 1.8v 250ma into PP1V8. While my supply wasn't reporting any draw, the restore did complete successfully. The only conclusion I can come to is that I need to replace the regulator again.
 
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PaulPCGuy

Member
Replaced the regulator again, we have 1.8V naturally now. I reassembled it and trackpad is now detected but it and the keyboard still don't do anything. I'm doing another DFU with everything connected in the hopes that it fixes it, though I doubt it. If it doesn't I'll replace trackpad. I know the keyboard works at least to an extent because again it does respond to the DFU key combination.
 
2informaticos

2informaticos

Administrator
Staff member
"I know the keyboard works at least to an extent because again it does respond to the DFU key combination"
Wrong assumption!
DFU keys are hardware ANDed (also inverted) by UT103.

Non working trackpad also blocks the keyboard.
Check if it gets all voltages.
Try known good trackpad board/flex.
 
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PaulPCGuy

Member
All voltages are present.

Testing with 3 different trackpads and 2 different cables (one new, one used), I have found this:


- 2 of the trackpads were from an A2338, 1 was from like an A1706 I think. With the two from A2338, they are detected but unresponsive.
- When attempting to enter diagnostics with either A2338 trackpad, it will hang indefinitely when trying to transition to the tests menu
- Diagnostics run fine with A1706 trackpad, and MRI reports trackpad not detected as expected
- With all 3, trackpad and keyboard both unresponsive.


I don't have another board to test with at the moment, does this sound more likely to be bad trackpads or a board issue?
 
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PaulPCGuy

Member
I was only able to check IPD and AMR_LEFT, RIGHT seems to be inaccessible without removing the sensor. Unless there's a TP for it, which FlexBV doesn't seem to be highlighting. And how should I test lid close? Just hold a magnet over it?
 
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PaulPCGuy

Member
Alright, did some testing. Lid closed RIGHT goes low, LEFT stays high. IPD_LID_OPEN_R_1V8 stays high open/closed. Looking at the BV, the LAS gets 1V8_AON and LEFT. Unless the BV is mislabeled, I find it very strange that only RIGHT goes low when lid is closed. That's not even accounting for the fact that IPD stays high even when closed.

I also noticed something, RIGHT goes high at 1.8V, LEFT goes high at 1.6V.
 
2informaticos

2informaticos

Administrator
Staff member
"I also noticed something, RIGHT goes high at 1.8V, LEFT goes high at 1.6V"
This is not a problem.

"Lid closed RIGHT goes low, LEFT stays high"
Looks like JR200 is bad; change it.

"IPD stays high even when closed"
That is caused by JR200; LEFT/RIGHT signals are ORed by UR200.
 
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PaulPCGuy

Member
2informaticos said:
"I also noticed something, RIGHT goes high at 1.8V, LEFT goes high at 1.6V"
This is not a problem.

"Lid closed RIGHT goes low, LEFT stays high"
Looks like JR200 is bad; change it.

"IPD stays high even when closed"
That is caused by JR200; LEFT/RIGHT signals are ORed by UR200.
Click to expand...



I replaced both JR200 and UR200. The circuit behaves normally now. However, when both LEFT and RIGHT are low, thus causing IPD_LID_OPEN_R_1V8 to also be low, the screen does not turn off. This was tested both out of the chassis with just a backlight and manually holding magnets, and assembled with the trackpad connected but removed from the chassis so that I could see the screen while closed.


This is just getting more and more confusing. Could U8100 be bad? That's the only thing I see connected to that line aside from the touchbar connector and trackpad connector.



Alright, this just got even weirder. As i was typing this reply, I saw the screen cut off. This is a fresh installation so it was just the timeout. However it did turn back on when opening the lid. I opened/closed it a couple times and the screen is now turning on/off like it should. The keyboard and trackpad still aren't working.
 
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PaulPCGuy

Member
Just triple checked JT400, all voltages are indeed present. The page 84 level shifters all appear to be getting the correct voltages and outputting correctly too. I don't see any signs of damage in that area.

At this point, the only thing I can think of is I got very unlucky and have two bad trackpads. I'm most likely going to just buy a new one.
 
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