KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

[duwane]

Hi all. I hope someone has come across something similar, as I am baffled.

I have a faulty logic board from a 2015 A1502 Macbook Pro Retina (820-4924-A). Some signs of liquid, but all corrosion cleaned, and several components refloated or replaced to eliminate any visually corroded areas of the board.

Machine boots fine now, but the keyboard and trackpad do not work at all when booting normally into Catalina, Big Sur, or Monterey. At the login screen, the cursor does not move at all when moving on the trackpad, and no keys on the keyboard respond on screen, however the machine does make a sound when any key is pressed (The sound is the keyboard buffer full sound).

Plugging in an external keyboard and/or mouse also does not work. Neither respond (except for the keyboard buffer full sound which is also present with an external keyboard).

The strange part is that booting into safe mode and recovery mode, both the keyboard and mouse function 100% normally without issue. Machine is stable and screen behaves normally in recovery mode and safe mode.

Another issue which may or may not be related, the screen slowly fades to black when not in recovery or safe mode. What I mean is it's like the brightness is reducing just like when the screen dims due to inactivity but seems to happen slower than normal screen brightness reduction due to inactivity, but not 100% sure this isn't just normal behaviour. At one point the screen also showed a white fading border, but that seems to only have been seen a couple of times.

I have swapped the logic board into a known working chassis (thus a different trackpad/keyboard ribbon cable, trackpad, keyboard, power board, and screen, etc.), and had the exact same issue, so problem follows the logic board.

I have done fresh installs of Catalina, Big Sur and Monterey, on different drives and same result. KB and trackpad work fine in recovery mode until first boot into the new OS, then neither respond again (and external kb and mouse do not respond).

My initial gut feeling was a bad hall sensor, but it does not fit with the symptoms completely as external keyboard and mouse also do not work when booting normally.

I have checked both logi.wiki, and repair.wiki, and the only things they recommend are changing the trackpad ribbon cable, and a potential issue with the hall sensor, so no help there.

Has anyone ever had a similar issue, or any ideas as to what I can try changing to fix this?

Any help or thoughts appreciated. Cheers.

[mon2]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

When the display is full on, check the backlight voltage.

When dimming, check it again.

Also check for corrosion of the backlight area including pwm, I2C lines, lcd backlight led return lines on the lcd connector.

Perhaps backlight led driver is defective - they do go often and we are replacing these as a general wear item.

Check the I2C voltages to see if there are stuck lines.

[reformatt]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

The reason it works in recovery is that Apple utilise the USB_TPAD data lines in that mode. Whereas in MAC OS, it uses the TPAD_SPI lines instead. You'll find the trackpad will work fine if you install Linux BTW, since that driver uses USB. It's only the MAC driver that uses the SPI interface.

So first, check you have the TPAD_SPI_BUS_EN present via U4910 (hopefully not a PCH issue). Then check the data/clock lines for TPAD_SPI.

[rotceh_dnih]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

As above i just recently had the same kind of issue where it worked on my live boot test usb but not in macos so i knew it must have been a SPI issue and my fix was repairing one missing connection on the trackpad cable.

worth running a continuity test "No power No battery" on each of the trackpad lines then confirming the data lines are ok , here i just measure in dc and if i see slight swings in voltage its normally safe to say its talking but a bus pirate is always handy here aswell or even a cheap logic analyzer.

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

The reason it works in recovery is that Apple utilise the USB_TPAD data lines in that mode. Whereas in MAC OS, it uses the TPAD_SPI lines instead. You'll find the trackpad will work fine if you install Linux BTW, since that driver uses USB. It's only the MAC driver that uses the SPI interface.

So first, check you have the TPAD_SPI_BUS_EN present via U4910 (hopefully not a PCH issue). Then check the data/clock lines for TPAD_SPI.

Thanks that makes sense. I have checked TPI_SPI_BUS_EN = 3.33v, and TPAD_SPI_IF_EN on pin 6 of U4910 is 3.33v as well. Not sure if these are the normal voltages, but they are present at least.

If TP SPI is the issue, then it doesn't really explain why an external USB attached keyboard and USB wireless mouse don't work during a normal boot as well (or does it?). Also, how would the trackpad SPI affect the keyboard as well?


I know the USB ports work, as external USB keyboard and USB wireless mouse work in safe mode as well, and have also attached USB sticks and external drives which all work (even during a normal boot).

I don't have an osciliscope, so am not able to check the data/clock lines for TPAD_SPI. Tried the measure them with a multimeter, but no dice, so guessing a scope is required.

I am going to try to boot the machine in the chassis with no trackpad or keyboard attached and see if external mouse and keyboard will work. Otherwise, I have another 4942 board here waiting for some components to arrive. Once they do, I will at least have a reference board to check voltages etc, but for now, it is still a bit of guess work.

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

When the display is full on, check the backlight voltage.

When dimming, check it again.

Also check for corrosion of the backlight area including pwm, I2C lines, lcd backlight led return lines on the lcd connector.

Perhaps backlight led driver is defective - they do go often and we are replacing these as a general wear item.

Check the I2C voltages to see if there are stuck lines.

Thanks, I will check the backlight area again too. This seems to relate more to screen brightness only, so not sure it could affect keyboard and mouse functionality as well?

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

As above i just recently had the same kind of issue where it worked on my live boot test usb but not in macos so i knew it must have been a SPI issue and my fix was repairing one missing connection on the trackpad cable.

worth running a continuity test "No power No battery" on each of the trackpad lines then confirming the data lines are ok , here i just measure in dc and if i see slight swings in voltage its normally safe to say its talking but a bus pirate is always handy here aswell or even a cheap logic analyzer.

Thanks, I did try the board in another known good chassis (my test chassis) and used the trackpad cable from the test chassis and had the same results.

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

So I booted the machine with trackpad/keyboard cable diconnected, and had the exact same result. External keyboard key presses result in a keyboard buffer full sound for every key pressed. External usb mouse didn't work either.

Also just noticed that the screen fade I mentioned is more like the background getting lighter rather than the foreground getting darker. By the time nothing can be seen on the screen, on black background with the white apple logo while loading (it took a while as I was booting from a slow external USB connected drive), the background is a light shade of grey, and the apple no longer visible. When turning off power, the screen returns to a solid black, so the screen issue could well be related to backlight or related. Will check this out in the morning (it is alredy 11:30pm here)

[reformatt]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

Review all voltages/signals to the trackpad. Keyboard data routes through the trackpad via I2C. Might be worth checking I2C_TPAD_SDA/I2C_TPAD_SCL and the pullups R5370/R5371.

MAC OS expects to communicate to the SPI interface for the trackpad. Unfortunately, these go to the PCH. Have heard of these lines getting fried unfortunately. If all the volts and enables check out, then you'll need a scope to go any further.

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

Review all voltages/signals to the trackpad. Keyboard data routes through the trackpad via I2C. Might be worth checking I2C_TPAD_SDA/I2C_TPAD_SCL and the pullups R5370/R5371.

MAC OS expects to communicate to the SPI interface for the trackpad. Unfortunately, these go to the PCH. Have heard of these lines getting fried unfortunately. If all the volts and enables check out, then you'll need a scope to go any further.

Thanks. I will go through i2c voltages with a fine tooth comb as that does sound like a likely candidate, and borrow a scope too if needed.

I did however do some additional testing today while the board was in the chassis, and it looks like it has some SMC issues. The fan does not come on at all.

I am not sure that a bad SMC could cause the KB and trackpad issues, but it would make sense that as many things as possible get throttled to prevent overheating, so may be the cause of the KB/trackpad issue too. Either way the SMC issue needs to be sorted out regardless.

At least the SMC issue explains the screen fade, as it is probably thermal throttling to keep the device below critical temp. Would also explain why external kb and mouse don't work, as USB ports are probably throttled too, or overheating.

I will try to refloat the SMC, but I suspect I will have to wait until I can source a board with matching SMC so I can do a swap. Once I can get hold of one I will be able to confirm if this also caused the trackpad keyboard issues as well.

Know of any good trustworthy sources for a selection of SMC chips with firmware? lol

[piernov]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

4924 only spins the fan when CPU goes above ~80°C. Throttling is related to reducing CPU speed.

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

4924 only spins the fan when CPU goes above ~80°C. Throttling is related to reducing CPU speed.

Oh wow ok thanks. I am not used to this model. Looks like I2C still the most likely candidate for now then. And looks like I need to test a bit more to make sure the fan does actually turn on.

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

So after letting this sit for a while, I finally got back to it and did some more testing.

If I plug an external screen/TV in via HDMI, everything springs to life. The keyboard and trackpad start working, and also external keyboard and external mouse start working. If I unplug the HDMI cable, everything works for a few seconds, then trackpad and keyboard (and external keyboard and external mouse) stop working again and cursor just locks up. Caps lock key still works on KB however.

Also, the first time I log in after starting up with an HDMI cable plugged in, once I get to the desktop, OSX shows a message saying that my keyboard type could not be detected and wants me to run a keyboard identification wizard, however no matter what key it tells me to push it says it can't figure out the keyboard type. I have tested all keys on the keyboard, and they all work fine.

This is such a strange one.

Any ideas why KB and trackpad only work when HDMI external screen is attached?

[piernov]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

If the image is frozen, it's not a touchpad/keyboard problem but an image problem.

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

If the image is frozen, it's not a touchpad/keyboard problem but an image problem.

Sorry, badly worded. What I meant was only the cursor locks up, meaning when I move on the trackpad nothing happens (cursor doesn't move).

When I play a Youtube video, if I unplug the HDMI cable while it is playing, it carries on playing and the keyboard and mouse continue to work. When the video ends the keyboard and mouse stop working again.

Could it be power saving related somehow? I have checked the hall sensor, and that works.

[duwane]

[SOLVED] Re: KB and Trackpad only work in safe mode - 820-4924-A MBP Late 2015 A1502

So I have managed to solve this issue, and thought it would be good to come back and update in case anyone has a similar issue in the future (as this thread seems to come up first in Google for searches for this type of issue with this board number).

I managed to get hold of another 2015 A1502 with known good keyboard, trackpad, and screen. Swapped the "faulty" board into the chassis, and problem was resolved, and everything works as it should. After swapping out screens, trackpad cables etc, I manged to establish that the screen is in fact the culprit! A working screen on the same chassis that I was experiencing the issue with resolved the problem.

I am still completely baffled how a faulty screen can present in the way that this fault presented itself, and would be really interested to hear anyone's theories on how a faulty screen can cause the trackpad and keyboard to only work when an external screen is connected via HDMI? At one stage I even thought of scrapping the board due to a PCH fault, as everything seemed to point in that direction, as the screen was going to sleep when it shouldn't, and keyboard and trackpad would stop working unless connected to an external screen via HDMI.

It feels so wasteful having to replace an entire screen when the existing one works, but only under certain conditions.

All I can think is that the faulty screen is chattering on the SDA/SCL lines causing the strange behaviour? Are the SDA/SCL lines even shared between screen, trackpad, and keyboard? Why did KB and trackpad work without external screen in recovery mode/safe mode, but not in OSX? How did a faulty screen cause external keyboard and external mouse to also not work unless connected to an external screen?

Between my posts in this thread back in April and now (June) I did change several IC's on the board (U4820, U4830, U4850, U4910, and re-balled the SMC), but never managed to improve the issue, so I suspect initially there were several problems, some of which were resolved by the IC replacements, but the final fix was a working screen.

[piernov]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

Again it sounds like an image problem and not a touchpad/keyboard problem. If image is frozen you won't see the result of using mouse/keyboard, however caps lock and audio were still reacting. Can probably also adjust volume with volume keys, and even "blindly" type some text in a text box then plug HDMI to see what has been written.
Usually this problem manifest itself with artifacts and random patterns on the internal display when external display is unplugged. Cable could be the problem if you're very lucky.

[duwane]

Re: KB and Trackpad only work in safe mode - 820-4924-A Macbook Pro Late 2015 A1502

Again it sounds like an image problem and not a touchpad/keyboard problem. If image is frozen you won't see the result of using mouse/keyboard, however caps lock and audio were still reacting. Can probably also adjust volume with volume keys, and even "blindly" type some text in a text box then plug HDMI to see what has been written.
Usually this problem manifest itself with artifacts and random patterns on the internal display when external display is unplugged. Cable could be the problem if you're very lucky.

Fair enough. I hadn't thought about it that way. You are correct as I tested typing before plugging in the HDMI cable, and I can see what I have typed after plugging in the HDMI.

Sadly I tried replacing the LVDS cable, and the problem persists, so sounds like it is destined for the scrap heap.