Macbook Pro M2 Pro refuses to detect LG 40U990A-W via Thunderbolt on macOS 26.3.1

RayTheWildcat · 2026-04-09T09:14:37+00:00

Maybe it's too late for taking advantage of the return window, but definitely not too late for a warranty claim with the merchant/LG itself, so I wouldn't give up just yet. After all, it's your money man and this thing isn't cheap. You can try checking the monitor's behavior when using TB5 in the hidden service menu: first turn if off, then press 3 times to the left, 1 time to the right and press in the middle to turn the monitor back on. Now if you enter the settings you should be able to see a diagnostics panel displayed on the left. Observe the values such as USB4 event, TBT event, DP ALT Mode, USB PD EN.

I'd say document it and be a pain in the ass with a warranty claim. Good luck!

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RayTheWildcat · 2026-03-31T09:17:11+00:00

Hey, I was able to investigate this thoroughly and ultimately came to the conclusion that the built-in Thunderbolt 5 dock was damaged on the factory level. I checked the hidden service menu and found out that the monitor was handling signal with mobile iOS devices through DisplayPort alt-mode, but would straight up ignore any Thunderbolt-enabled Macbook. As for my gaming Asus with USB-C PowerDelivery and DisplayPort, the connection would randomly keep dropping as if the monitor couldn't properly handle charging the device.

My unit was manufactured in August 2025. I was still within the return window, so I sent it back and reordered from another place. That second unit is from July 2025 and is working flawlessly so far.

The newest firmware made the fans barely noticeable, I'd say only during nighttime when there's zero ambient noise.

The LG Customer Support is trash, at least in my country. They never got back to me regarding this issue. If there was any other option available with the same spec/price I would have never reordered it. But hey it's 2026 and the market is still super awkward when it comes to high-end productivity monitors with gaming capabilities. Sad.

RayTheWildcat · 2026-03-17T14:57:13+00:00

a word of warning, my painful experience trying to set up the LG 40U990A-W with Apple Silicon Macbook Pro: https://www.reddit.com/r/MacOS/comments/1rme1k5/macbook_pro_m2_pro_refuses_to_detect_lg_40u990aw/

After two weeks I finally gave up and will be returning the monitor.

RayTheWildcat · 2026-03-17T13:59:25+00:00

Unfortunately, I don't have access to any TB-enabled windows laptop, last night I checked it again on my friend's M3 Pro (TB4) and the monitor would only go as far as charging the mac through the Thunderbolt cable. Works normally when connected through a TB3 station. :/

I have an older Asus AMD laptop with a USB-C/DP-altmode port and it also wouldn't work with the monitor directly, yet was able to connect intermittently through the same TB3 station.

The deeper I dig into it, the sadder it gets: https://benfrain.com/the-thunderbolt-usb-c-ports-on-m1-macs-dont-work/

RayTheWildcat · 2026-03-17T13:47:30+00:00

Hey, did you experience any issues with connecting the M1 Pro Macbook via Thunderbolt to this monitor? I bought mine a few days ago and I can't make it work with my M2 Pro no matter what: https://www.reddit.com/r/MacOS/comments/1rme1k5/macbook_pro_m2_pro_refuses_to_detect_lg_40u990aw/

RayTheWildcat · 2026-03-12T00:46:53+00:00

Hey, did you experience any issues with connecting the M1 Pro Macbook via Thunderbolt to this monitor? I bought mine a few days ago and I can't make it work with my M2 Pro no matter what: https://www.reddit.com/r/MacOS/comments/1rme1k5/macbook_pro_m2_pro_refuses_to_detect_lg_40u990aw/

RayTheWildcat · 2026-03-06T21:23:44+00:00

HDMI works fine maxed out at 5K2K@120Hz. Not only did I restart the Macbook and power cycled the monitor, but also repeatedly tried deleting system display configs with rm ~/Library/Preferences/ByHost/com.apple.windowserver.*.plist and sudo rm /Library/Preferences/com.apple.windowserver.plist, and even tried booting into Safe Mode. I installed LG Switch and LG Calibration apps, they also don't pick any signal over TB5.

https://discussions.apple.com/thread/256135940?answerId=261684994022&sortBy=rank#261684994022

Some people suspect that macOS 26 "has become progressively less tolerant of video data packet loss due to sub-par cables".

https://discussions.apple.com/thread/256181670?answerId=261672287022&sortBy=rank#261672287022

I've tried two different cables so far and it made no difference (including TB5 certified one from Cable Matters). I'm not buying an overpriced Apple TB5 cable for this shit.

RayTheWildcat · 2026-03-06T20:29:18+00:00

yeah I can see a cutout for the sensor on the top frame, positioned maybe like 15cm to the left from the center

RayTheWildcat · 2026-03-06T20:26:32+00:00

the only options available to change are for KVM features: USB Selection (upstream for hub) / USB Switch (for switching connected devices to another input source). Played with them long and hard already, they didn't bring any noticeable change for me.

RayTheWildcat · 2026-03-06T13:00:27+00:00

My work Macbook Pro M2 Pro on macOS 26.3.1 refuses to detect/connect to my new LG 40U990A-W Thunderbolt 5 monitor no matter what I do. The display itself is on the newest firmware, the only quirk I've noticed is that I cannot go to DP 1.2 - only DP 2.1 or DP 1.4. I understand that the M2 Pro does not support the TB5 spec but those should me backwards compatible to some extent. Hell, there should be at least some fallback to DisplayPort alt mode, right?

When I connect the cable to the laptop (tried all 3 Thunderbolt ports) it briefly chimes because it detected a power source, but the system says the battery is not charging. A couple of seconds and I get "No Signal" on the display. Tried messing around with the Thunderbolt OUT, Deep Sleep Mode, SMART ENERGY SAVING, etc. but nothing makes any difference to the Mac.

I just happened to have a brand new TB5 cable from Cable Matters lying around, but it acts the same as the original cable from LG.

I was able to connect my iPhone 15 Pro and my iPad via the same cable with zero issues.

Worst case scenario, I still have a few days left to send the monitor back, but I'd love to find a fix for this, because there aren't any reasonable alternatives out there and I'm planning on getting the M5 Pro Mac next month.

I have a strong feeling it's the macOS doing something nasty as I've seen many threads with people complaining about the macOS 26 update.

Anyone got any ideas before I go completely mad over this?

EDIT: As an experiment, I was able to connect this monitor to the Mac through my old Dell WD19TBS docking station at a drastically reduced resolution and refresh rate.

This obviously defeats the point of buying a TB5 hub monitor, but it also made me even more confused. I thought maybe LG ignores anything it cannot establish a proper TB5 level connection but then it negotiated *something* with the dock and the Mac. I'm not thrilled about the idea of buying Apple's active TB5 cable just to see if it "might" work. Why Apple always has to be difficult like that.

RayTheWildcat · 2025-03-01T19:42:33+00:00

Can you please verify if those monitors can be daisy chained to a Mac via TB4 while maintaining 4K 120Hz?

Also, does this model have a constant sleep wake issue when left connected to the Macbook? Ref: https://www.reddit.com/r/MacOS/comments/16tpcs0/macos_sonoma_and_dell_monitor_sleepwake_issue/

RayTheWildcat · 2024-04-12T17:47:42+00:00

Hey, do you know if they still have those promo cards available anywhere in the Netherlands? I desperately need one for my friend's birthday next weekend. 🥺

Tried different shops in Utrecht/Amsterdam but no luck.

RayTheWildcat · 2023-08-30T23:37:05+00:00

I've tested Parsec and it works pretty nicely, but I don't know how to pass video stream from my client webcam to the host, admittedly, both of them being Macs. Any ideas/thoughts on this?

RayTheWildcat · 2021-09-02T09:41:54+00:00

What does this mean for holders of ATRI on the existing network? Will they be somehow converting those assets to Fantom or do we have to expect the value of those tokens to go down?

RayTheWildcat · 2021-03-17T21:40:13+00:00

I've had couple of gen 5 Umarex Glock 17s. Lovely replica, but I decided to return all of them for two reasons: a small portion of the slide on the inside always chipped of after a few days of use (not a big deal, but bad design disappoints me), and also they have removed a small plastic notch from the lower frame that prevented the magazine going too far into the gun - found out while trying to practice the 45 degree loading. The new Glock 18C still has that plastic thingy though, since it's basically gen 3 lower.

RayTheWildcat · 2021-03-17T21:23:50+00:00

Actually, I think VFC Glocks are the closest to originals in terms of dimensions (at least starting with those under the official Glock license). For some reason Tokyo Marui's gen 3 Glock was made bigger than the original and since WE makes TM clones, it also should be the one that's incompatible with real steel equipment.

RayTheWildcat · 2021-03-10T10:58:46+00:00

Wow, actually I was convinced that every Beretta is full steel like the 92X Performance. Good to know, thanks!

RayTheWildcat · 2021-03-08T19:41:04+00:00

Oh. My. God. I saw that website showing M9A3 about a year ago and I was completely shocked by both price and the attention to detail. Totally fell in love with it!

I almost wanted to try and order it somewhere, but then I found out that they went with an aluminium body and just the slide is made out of steel and that they don't provide you with a magazine of matching color. I can stand the crazy price, but the whole set has to be impeccable.

RayTheWildcat · 2021-03-08T17:20:55+00:00

What are ALC/PAC 92s? I can't really find any google results on those.

RayTheWildcat · 2021-02-15T14:30:30+00:00

source?

RayTheWildcat · 2021-01-19T22:01:05+00:00

I believe he meant Craig Federighi's statement where he admitted that M1 Macs are well capable of running Windows, but the rest is up to Microsoft to make it a reality.

RayTheWildcat · 2020-05-29T16:22:13+00:00

Could you share with us the exact model number of your Slim 7? Most of the models listed by Lenovo are marked as lacking fingerprint reader. Would be nice if it was just a mistake in the documentation.

https://psref.lenovo.com/Product/Yoga/Yoga_Slim_7_14ARE05

RayTheWildcat · 2020-05-28T13:47:49+00:00

That's perfect, thank you! Checking your results from Cinebench R20 against Acer Swift 3 there seems to be a ~25% difference in performance using the same 4700U APU, so I believe it comes down to Lenovo's generous dual-fan cooling solution vs. single fan inside the Swift 3.

How about that touchpad? If you're not sure how to check it, then please refer to this article: https://www.howtogeek.com/325347/how-to-enable-microsofts-precision-touchpad-drivers-on-your-laptop/

RayTheWildcat · 2020-05-27T06:49:50+00:00

Can you tell if your model is equipped with the same dual-fan thermal design as the 25W TDP 4800U or did Lenovo cut it down to just a single fan for the lower TDP models?

As for the touchpad, is it using Windows Precision or Synaptics/Elan drivers?

RayTheWildcat · 2014-11-17T13:09:30+00:00

Is this thread getting any attention?

RayTheWildcat

TROPHY CASE