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Repair guides and disassembly information for the MacBook Pro 16'' released in November of 2019. Model A2141, EMC 3347.

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White line flash/flicker on external display

The last week I’ve experienced a weird bug / glitch that I’m unsure of what is causing it.

For my 16” MacBook Pro I got a BENQ PD2700Q monitor connected through a HDMI -> Apple USB-C Adapter -> MBP.

The flicker I experience appears EXTREMELY quick and with no apparent pattern. I always notice it with my eye and had to record with my iPhone XS Max in slow motion to catch a picture of it. It does not appear at all on the built in 16” display, only on the external display.

I made a GIF of the flicker seen here: https://imgur.com/EnEXKqn

For clarification, marked in red here: https://imgur.com/gREjAyg

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When recording that, the only thing I did just before (1 sec or less) is moving / clicking with my mouse. Looking at it frame by frame its gradually appears, becoming clearer, peaking and then fading.

The laptop haven’t been moved since February since i’ve been working from home and I bought it in December. Its currently in perfect condition. So no physical damage that could have caused it.

What info I got now:

  • White, small horizontal lines appearing for a few ms.
  • Seems to only happened on the left “half” of the monitor.
  • Does only happened when Im using the computer, tried having it on idle / doing nothing without any flicker occurring.
  • GPU & CPU temps are all stable and normal. Performance is as expected.
  • No stuttering or performance degradation when it happens.
  • No “pattern” to it, happens at random intervals but tend to be sometimes a 30 minutes wait between each time and this morning it hasn’t happened in 4 hours (So far). Seems to be triggered by activity on the display such as video playing, scrolling, playing video games (World of warcraft Classic, so not performance intensive).
  • Resetting the NVRAM & SMC seems to fix it temporarily for a few hours / up towards a day.
  • Refresh rate on both monitors is set to 60hz at default resolutions
  • When using only the built in display, I forced it to only use the high performance / dedicated GPU since I thought it could be related to it, no flicker.
  • Used to have everything connected to the right side of the computer, 1x digital av adapter with power, hdmi + webcam connected through one usbc and next to it I had the usbc - USB adapter with my mouse.

Currently only got HDMI connected to the AV adapter, power on left side ports.

Software changes done recently:

  • The only software change i’ve done is installing Citrix Receiver / Workspace to access Bloomberg Terminals from home (Had to reinstall it twice due to glitches)
  • Disabled and later enabled the battery health management (to see max capacity with it turned off)

Currently testing:

  • Running at a slightly lower resolution (2048x1152)
  • Cleaned the HDMI cable ends + ports on adapter and monitor with compressed air (Only got 1x cable + 1x hdmi port on the monitor).
  • Running with True Tone, Night shift and automatic brightness adjustment disabled.
  • Testing the display with my partners Early 2015 13” MBP (No DGPU), no flicker from what I have noticed (currently testing this)

Have not tried:

  1. Reinstalling OSX
  2. New HDMI Cable & Apple AV Adapter
  3. Checking monitor internals since I live next to the ocean (eastern Australia) so corrosion has happened on other electronics such as TV ports and the monitor is +2 years old with heavy daily usage. So salt water in the air could be a potential factor.

HWINFO:

  • BENQ PD2700Q Running at max res (2560x1440, default res)
  • 2.3Ghz, 8 Core I9
  • 16gb DDR4 @ 2667Mhz
  • 5500M 8gb
  • Catalina 10.15.6
  • Some cheap bluetooth mouse from office works connected to the laptop through a usb-a receiver connected to a usb-c -> normal USB adapter from apple.
  • Magic keyboard.

If anyone has any idea on what could be the cause behind this I’m glad to hear :-).

Cheers

Note 1: Running on lower resolution seems to fix the flickering to some degree, I’ve been running it on the "one step lower" (2048x1152) resolution for 8+ hour without any flicker. I switched back to 2560x1440p (default) and the flicker has so far happened 3 times within 45 minutes.

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I have a flashing/flickering issue as well with my new MBP 16" on all external displays that work fine with my MBP 15" (2018).

Went back into service, they changed out the motherboard, without improvement.

After some Googling I found out that there are sooo many people having issues with the new MBP 16" and external displays that I must conclude that it is a design issue and not an isolated failure. (https://discussions.apple.com/thread/250...)

I just upgraded to the latest OS 10.15.6 (above thread suggested it was solved as of 10.15.4) but no improvement at all.

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@kristoff.henry

"Good" to hear that we're not alone! (I also found some discussions on stack exchange regarding a similar problem with the 16")

Since my last post and messaging with Dan, I've been experimenting with running a custom resolution on my external display with the app "SwitchresFX".

The native resolution is 2560x1440p and I've been running it first on 2500x1400@60hz with quite positive results with the flickering nearly disappearing completely.

Also a 2560x1440@58hz which has so far resulted in less flickering but instead the flickering has "moved" From the lower left quadrant of the display to the upper right and is "longer" in horizontal length, so it seems seems that full resolution is the culprit and not the refresh rate.

The test with running it at 2500x1400@60hz or 2048x1152 both gave me less flickering / no flickering at all so my guess is software problems.

I'm going to install the Big Sur public beta later this week and I'll report back on the results! :-)

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Wow a very through write-up!

I fear your system is the issue here. The data path of your video signal goes through a few steps before it gets to the USB-C port and onwards to your external display unlike your internal display (very short path). Its something in this pathway internally that’s messing you up.

Let’s give this a try go into your Energy Saver preferences (you’ll need to unlock it) alter the Automatic graphics switching setting so your system is forced to use the discreet GPU only by unchecking it.

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When you look at the About This Mac the GPU listed should be your AMD GPU. Did that alter things? Find out which graphics processor is in use on your MacBook Pro

I haven’t tried this great utility on the newer MacBook Pro’s or Catalina (no 32bit support) so I’m not sure if it works gfxCardStatus which is a bit easier than always fumbling with the Energy Saver.

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Hah, I have worked as a tech support years ago so I know first hand how much a proper explanation helps in troubleshooting ;-).

- I unchecked the Automatic graphics switch a few days ago since I thought that could be the culprit but no change since it still flickers occasionally.

I also tried just installing the gfxCardStatus like you mentioned and it also tells me that the d-gpu is the one active :-).

I've also been monitoring the"Intel power gadget" to see if there is any power / thermal spike when it occurs but nothing that I can see, I also checked the electricity outlet the computer is connected with and no interference / spikes occurring there.

When you say that the "system" is the issue, do you mean the hardware or software system? Keeping my fingers crossed that its just a software bug ;-).

Its very...interesting that It doesn't flicker / flash at all when running a slightly lower resolution so either its something with the software I guess or that the resolution affects the hardware?

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Let's also try forcing the system to use the Intel I-GPU only to see if that changes things.

I'm not sure if you have a hardware or software issue. As you don't see the issue on the internal display I'm thinking the issue is within the Thunderbolt port hardware as you stated you didn't encounter the issue earlier.

The other possibility is your use of Citrix Receiver / Workspace app altered the drivers in some way that messes it up.

Which came first the chicken or the egg kind of problem ;-{

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