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...
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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....
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Re: 820-01814-A Touchbar not functioning
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...
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Re: A2251 touch bar causing system crashes
I wish I could help you with this. I similarly had the touchbar display this scrambled static. Unfortunately in my case it was water damage and a new touchbar and connector did not fix the issue.
I'm curious if you managed to get this to work as I have tried a lot to get my a1990 going, to no avail.
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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.
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Re: 820-01814-A Touchbar not functioning
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....
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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.
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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
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Re: 820-01814-A Touchbar not functioning
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...
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Re: 820-01814-A Touchbar not functioning
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...
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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,...
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820-01814-A Touchbar not functioning
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...Last edited by Jamo33lovelock; 09-06-2022, 05:24 PM.
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Re: New Members - please post your introductions here
Hi all,
I'm James, I live in the US, about to be Canada, and I repaired devices as a hobby. As such my experience is currently limited and I'm here to read and absorb, hopefully to get some advice as well. Thanks to all that contribute to the community, it's awesome.
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