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A1708 / EMC 2978 — Lanzada en Octubre 2016, este MacBook Pro de nivel básico retiene sus teclas tradicionales de función (en lugar del OLED Touch Bar). La versión con teclas de función incluye un Intel Core i5 y dos puertos Thunderbolt 3.

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MacBook Pro turns on 1 time out of 10, black screen with backlight on

I’m a repair guy and I got this late 2016 A1708 into repair with strange behavior problem. Came in for repair as no boot. No liquid damage.

When I press the power button, the screen backlight turns on, but nothing else happens (CPU gets warm). If I disconnect battery and prompt it to boot via charger, there is a charger insertion sound every time, then backlight turns on, no image, and it’s clearly not booting (more symptoms below).

  1. For the first 3-4 seconds after pressing power button, pressing caps lock turns on and off caps lock LED. After that it stops changing state. If it were booting with no image, caps lock would work once I get to the login screen. But it doesn’t. No matter how long I wait.
  2. USB hub inserted into free type c port (not the one with charger) has an LED and it lights up OK and stays on forever. Both Type-C ports work ok.
  3. No image via Type-C -> HDMI adapter
  4. Tried known good screen, no difference.
  5. Obviously I tried all existing resets such as SMC, no difference
  6. Tried pressing on CPU, reseating connectors and stuff, no difference at all.
  7. Once every 10 boot attempts it actually does turn on and works seemingly totally OK, thus I was able to run some tests (have password, so unlocked boot from external device)
  8. As of writing this, memtest has been running for well over an hour, no errors in CPU-RAM connection department.
  9. Similarly, booting with D (Apple diagnostic) shows all OK.
  10. Removed SSD (PCIe dongle-like thingie in this one), disconnected other peripherals including keyboard, no difference in behavior.
  11. CPU temperature doesn’t affect it, hot or cold, it always boots like 1 out of 10 times.
  12. Power consumption on boot from charger without battery is ~400 -> ~700 ->570mA, then it just sits at 570mA and doesn’t change at all. Clear indication of something being “stuck”.

Has anyone met it or maybe someone recognizes some pattern or common problem? I’m kinda out of options as to what to try/test. Since the display backlight turns on, it’s obvious it powers up and all its power rails must be OK. Also, this occasional “turning on fine” thing is no help at all.

If it weren’t booting every now and then, I would look at its bios SPI flash, but this kind of behavior…I have no clue.

Update (11/11/2021)

Update: I may be reconsidering CPU temp statement. I'm inclined to believe it's a CPU-related issue, once I'm able to start it, will do CPU and iGPU stress tests, but it's too late for today already. Still, open to various suggestions.

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Are you sure you have a TouchBar model and not the Function key model? As the removable SSD is with the Function key (Fn) model not the TouchBar

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When you say power consumption on the charger, is it getting to 20 volts? Or is it staying stuck on 5 volts? I tend to dislike steady current draws.... It could be a CPU issue, but I'm less likely to think that if it's getting to the point where display backlight is on

Are you getting fan spin? Have you taken a close look at the board? You said no liquid damage, but are there any components on the board which look like they have an obvious issue, cracked caps, scorch marks, etc...

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As I've said, it behaves totally ok. Board visually ok (I'm an experienced board repair tech, checked all the stuff I could think of). Full 20V always, fan spins.

Yesterday after memtest however I couldn't make it boot anymore. Now I came to work and it turned on on 2nd attempt (while CPU was still cold). Will run stress tests on CPU and GPU right now since I got a boot. I'm suspecting dying iGPU. We'll see.

Had benchmarks for 2h, 75-80C most of the time (bottom lid was off). Now while it's hot it won't boot anymore, only black screen with backlight on over 20 attempts.

I think I'm gonna declare it a dead CPU. Evidence for CPU is, so to say, circumstancial, but it looks like a duck, quacks like a duck and boots like a duck. Will offer board replacement and data recovery and will call it a day.

Thanks for participating in the discussion (but the device is still here, so if there is some fresh idea, I'm all...ehm...eyes)

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Ilya estará eternamente agradecido.
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