820-01814-A Touchbar not functioning

[Jamo33lovelock]

Hi,

This is my first post asking for help, but I feel I have now reached a point where I am out of my depth entirely.

820-01814-A board model, purchased with knowledge it was faulty and had water damage that had affected the touchbar. Water damage was located around the touchbar connectors to the point there were open circuits. When turned on the touchbar would light up, but the entirety of it was scrambled colours and pixelation.

I replaced the topcase (wasn't comfortable doing a touchbar swap) expecting this to be a simple issue of an open circuit, but instead the touchbar now doesn't have any life. Thinking this was an issue with the new touchbar, I actually went and bought another topcase to rule that out. Note: this is a hobby so I'm not all that stressed about this not being the most cost-effective method, it's all a learning process.

I found damage on the J5100 connector so I removed added solder and placed the connector back. Afterwards I tested the connector for continuity from the pins (internally) to the corresponding points on the board. All checked out.
I have also replaced Q5100 and U5104, yet still no change.

I am trying to get voltage readings, but the test pads for these circuits aren't accessible while the board is in the case. So, please if there are any readings I should get that may help I will. I have initial readings, see below

PP1V8_SLPS2RSW_DFR - 1.806v
PP5V_G3S_DFR_FILT - 5.10v
PP5V_G3S - 5.11v
PP3V3_G3HSW_DFR - 3.386v
PP3V3_G3H_DFR - 3.385v
DFR_PWR_EN_R - 1.779v
IPD_LID_OPEN - 1.8v
IPD_LID_OPEN_R - 1.775v

Any help is greatly appreciated, and I will try get any readings needed to further diagnose.

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

I am still trying to figure out what is going on with this Touch Bar. I am beginning to think something has happened to the T2 chip or similar. I am confused how the entire system is working yet the keyboard preferences don't even acknowledge the existence of the Touch Bar, yet seemingly the voltages are present.

I would like to replace the capacitors and inductor in the circuit, but I do not know how to source the inductor, it doesn't seem to be standard specs. If anyone has any advice on where to find apple spec inductors, please let me know. I will continue to troubleshoot this laptop, until I get fed up and likely sell for parts to someone that can hopefully fix it.

The main issue I am facing is that I do not know how to circuit should behave when healthy, so I don't know if anything is wrong as the issue clearly isn't a blatant one.

[mon2]

Re: 820-01814-A Touchbar not functioning

Hi. Do not replace any caps / inductors / parts till more is known. This may just lead to other faults.

Does your unit boot to offer a display on the LCD ?

Can you see the LED toggle on the when you press the caps lock ? This confirms that the OS has booted.

If not, measure the voltage of PPBUS_G3H which is a vital must have voltage on all macbooks. Measure @ F7000 / F7001 fuses, pin # 1 - take your pick.

Post your measurement.

PS: The parts are quite generic and often can be sourced from Digikey / Mouser / Arrow / Mobile Sentrix if in a rush. If not in a rush - Aliexpress.

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

Hi. Do not replace any caps / inductors / parts till more is known. This may just lead to other faults.

Does your unit boot to offer a display on the LCD ?

Can you see the LED toggle on the when you press the caps lock ? This confirms that the OS has booted.

If not, measure the voltage of PPBUS_G3H which is a vital must have voltage on all macbooks. Measure @ F7000 / F7001 fuses, pin # 1 - take your pick.

Post your measurement.

PS: The parts are quite generic and often can be sourced from Digikey / Mouser / Arrow / Mobile Sentrix if in a rush. If not in a rush - Aliexpress.

Hi Mon,

I was actually just reading some of your replies on various other posts, so thanks for contributing to the forum so much!

I am actually replying to you now on the laptop. Everything about this Mac is functional, except the Touch Bar itself. This is where I am having the issue, no touch response, no Touch Bar LCD life, just plain nothing the entire time.

Sorry if that wasn't clear in my previous posts

[mon2]

Re: 820-01814-A Touchbar not functioning

A while ago we were faced with a touchbar unit that did not function. Replacement touchbars are available but may not function exactly like the original. Mobile Sentrix sells them.

If my memory is correct, suggestion from @Piernov was to perform a DFU restore using another macbook. That loads up some bootloader used by the touchbars.

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

A while ago we were faced with a touchbar unit that did not function. Replacement touchbars are available but may not function exactly like the original. Mobile Sentrix sells them.

If my memory is correct, suggestion from @Piernov was to perform a DFU restore using another macbook. That loads up some bootloader used by the touchbars.

I can see the Touch Bar and backlight In the T2 Bus as well, I don't know if this would be the case if the circuit wasn't functioning.

I am going to do the DFU restore now.
I think there is potentially a software issue and if you're right and Piernov said so, then I am inclined to believe this may be a fix.

Hopefully this works out

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

There was no change with the touchbar. But I did not have any issues whilst reinstalling OS or completing restore, so I'm curious if the touchbar works but isn't being told to wake.
If the laptop was in clamshell the touchbar wouldn't be on, so perhaps voltage is missing to wake it?

Somewhat at a loss now

[mon2]

Re: 820-01814-A Touchbar not functioning

Perhaps the touchbar is defective ?

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

Perhaps the touchbar is defective ?

I am inclined to say the touchbar is good, but I can't prove that really. I have another topcase which I could test the board in, but I was having the same issues in that topcase as well.

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

I've just been doing some live voltage measurements and found that DFR_DISP_RESET_L is at 1.8V, so I'm guessing this means the systems is holding the touchbar display in reset state.
I don't know where I would go from here, other than U3900 sending that signal, I don't know what values it needs to let go or inputs that are missing for it to function properly.
I also really do not know how to measure these voltages safely as the test pads are inaccessible with the board in the case and everything attached.

[mon2]

Re: 820-01814-A Touchbar not functioning

DFR_DISP_RESET_L

The suffix is '_L' which denotes ACTIVE LOW signal.

So if this line is LOW (0v or similar) then this line is in RESET (parked) mode.

Since you are higher than this voltage, the line is NOT in reset mode.

The touchbar themselves appear to be inexpensive in Asia and is a fancy LCD display. Perhaps it is damaged ? Do inspect the cabling as well on this touchbar.

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

The suffix is '_L' which denotes ACTIVE LOW signal.

So if this line is LOW (0v or similar) then this line is in RESET (parked) mode.

Since you are higher than this voltage, the line is NOT in reset mode.

The touchbar themselves appear to be inexpensive in Asia and is a fancy LCD display. Perhaps it is damaged ? Do inspect the cabling as well on this touchbar.

Yes, so the display reset signal is high when it should be low. But how am I to know why it is in this state?

All cables etc look great, I can test the board in another topcase, but that's all I can do really. This is a difficult circuit to get to, that's my biggest issue at the moment.

[mon2]

Re: 820-01814-A Touchbar not functioning

The reset supervisor circuit will keep this line LOW to reset and then release it so that it may operate with the graphics, etc.

An oscilloscope will be able to capture this quick pulsing of the reset line - perhaps even a low cost logic analyzer. The one concern with the logic analyzer is that you are at 1v8 levels.

Yes, you are working with smaller than cell-phone parts and definitely know of the pain. It really is a difficult unit to service, especially if it is your first one to repair.

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

The reset supervisor circuit will keep this line LOW to reset and then release it so that it may operate with the graphics, etc.

An oscilloscope will be able to capture this quick pulsing of the reset line - perhaps even a low cost logic analyzer. The one concern with the logic analyzer is that you are at 1v8 levels.

Yes, you are working with smaller than cell-phone parts and definitely know of the pain. It really is a difficult unit to service, especially if it is your first one to repair.

Yes, unfortunately I don't have that equipment anyway. So something must be wrong to put this in reset and hold it there. I just don't know how to find what.

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

I still haven't made any head way. I've taken a lot of measurements and I have tried to test with test pads but it is nearly impossible. The best idea I have is that the display is being held in reset. I'm reluctant to give up, but I am getting to the point where I don't think I have the knowledge or equipment to fix this fault.

[Jamo33lovelock]

Re: 820-01814-A Touchbar not functioning

The reset supervisor circuit will keep this line LOW to reset and then release it so that it may operate with the graphics, etc.

Sorry to revisit this, but I still have this MacBook and I refuse to give up. I am an annoyingly persistent person.

You mention here the reset supervisor circuit. I now understand that the touch (not the display as mentioned) is being held in reset (0 volts on the circuit). But, what contributes to the logic or supervisor circuit that causes the touch circuit to go low? Ie. How to I find the elements needed to allow dfr_touch_reset_l function properly? Without knowing which particular circuits are crucial to this, I don't know how to properly investigate.

[Jamo33lovelock]

Every now and then I have a look at this laptop in hopes that my experience gained can help me figure out why the touchbar will not function.

By comparing to an IC locked, but functional board I was able to prove that the touchbar works on the topcase I am using. Ruling out a bad touchbar.

I have then taken as many measurements as I could to compare the two boards in different states.
There are some clear issues but I cannot identify what the problem is.

With the logic boards only -
SPI_DFR_MISO_R - 1.751V on locked board. 1.291V on my board.

Logic boards fully connected -
SPI_DFR_MISO_R - 1.751V IC locked board. 0.270V on my board.
DFR_TOUCH_RESET_L - 1.8V IC board. 55.9mV my board.


So, touchbar is held in reset and something is seemingly pulling down the SPI circuit. All diode and resistance readings are comparable or there abouts.

How can I proceed? What is the laptop missing to enable the touchbar? Nothing else stands out between the logic boards at all, I have even swapped a few components that I was concerned about and still the results remain the same.

Any help is genuinely greatly appreciated.

[mon2]

Not at my desk so unable to confirm with the schematics but the DFR_TOUCH_RESET_L line should have a pull-up resistor. Locate it and confirm there is a pull-up voltage on this resistor. Next, remove all power and check the resistance across this resistor. Post all measurements.

[Jamo33lovelock]

Not at my desk so unable to confirm with the schematics but the DFR_TOUCH_RESET_L line should have a pull-up resistor. Locate it and confirm there is a pull-up voltage on this resistor. Next, remove all power and check the resistance across this resistor. Post all measurements.

I assume you are referring to R5103 a 4.7k resistor
On point 1 (PP1V8_SLPS2RSW_DFR) - 1.797V
On point 2 (DFR_TOUCH_RESET_L) - 54.5mV

4.62k reading.
Diode readings on R5103 - 0.552V on point 1 (PP1V8_SLPS2RSW_DFR). 0.480V on point 2 (DFR_TOUCH_RESET_L)

[Jamo33lovelock]

Out of interest I decided I would move some resistors aside, taking new readings between boards and see what the differences were.
Something odd that I found relating to the SPI_DFR_MISO R4866 line was that when I removed the 20ohm resistor and took measurements on either side of the resistor, there was a massive difference between boards.

My board
R4866 Pin 1 - 1.8V (SPI_DFR_MISO_R), Pin 2 - 1.131V (SPI_DFR_MISO)

IC Locked
R4866 Pin 1 - 1.8V (SPI_DFR_MISO_R), Pin 2 - 47mV (SPI_DFR_MISO)

Why would I have voltage on the input to the T2 if the resistor is removed? This goes to U3900[757].
Diode readings were the same, no shorts to other lines that I could find.

I may be oversimplifying this or completely incorrect, I am just trying to figure out exactly what is wrong here. Perhaps T2 is just fried on that particular circuit?