Question HP Spectre x360 display problem (likely HW)

[Cy_kkm]

I have an HP Spectre x360 15 notebook which has developed display problems, that I'm attributing to hardware. I like the notebook and prefer to rather repair it than replace. Custom configurations are assembled from unobtanium in these covid days, with lead times of 3-6 months, and those in stock rarely match what I want. I already replaced the battery once, and am typing away a second keyboard. I'm an EE, experienced enough to take it apart and put back together in a working shape with no extra parts left I also have a 'scope, a multimeter and all the stuff you normally find on an EE's bench, if any of it could help.

My question: Is this a display module problem, or a mobo problem? A complete description follows. I will be grateful for any hints and ideas how to tell which one of the two is failing.

1. Intermittent loss of vertical sync. If you had a TV 30 years ago, you know how it looks. If not, what happens is multiple copies of screen image whoosh upwards at a fast rate, maybe 10-15 times a second, so that multiple copies of the screen are visible at a time. There is no apparent pattern: sometimes multiple copies of the white HP logo normally centered on black screen during boot bunch together and happily bob up and down at any Y coordinate, before breaking the quadrille and appear spreading along the vertical strip top to bottom.
   The problem:
   • is aggravated by higher laptop temperature;
   • can be triggered at will when the laptop is warm enough by quickly decreasing brightness to the minimum, as fast as hotkeys autorepeat;
   • but may not be elicited by decreasing brightness one step every 15 seconds—I can get it stable all the way to the lowest brightness (but then it can suddenly lose sync again at a lower brightness setting);
   • is fixed by setting brightness to the maximum and displaying as much white on screen as possible (open Edge maximized with a Win+F1 shortcut—yay, Edge is finally useful for something!). Sometimes immediately, sometimes in up to 15 seconds the image stops its frantic scroll, unless the device is too hot. Then it helps to cool it down by lifting from the table (the airflow intake grille is at the bottom, and legs... aren't legs, they are tiny buttons);
   • sustains across reboot or even power down/up cycle. It seems a HW issue: firmware is unlikely to bitrot, and it happens well before any soft software bit gets a chance to run.
2. The brights drop yellowish-white strictly vertical ghosts on the darks above. For example, if I open an icon with white background in dark-themed Photoshop, there is a strip of yellowish tint sticking up all the way up from the image to the top edge of screen. If the icon I edit is not just a white square, darker image elements cast their own parallel darker ghost strips within this full image-width strip. This is most prominent at a higher brightness, but does not go away even at a mid-range setting, which is already too dark to work comfortably.

I would not take it for granted that #1 and #2 above are a single issue. I am not really sure, but I think #2 developed gradually over months before the much more annoying #1 started more recently.

I disconnected, cleaned contacts of both mating sides of all display connectors with the most nasty smelling contact cleaner spray at my disposal, and reconnected the display module, to no avail.

More info, if it helps: all HP firmware upgrades are installed long ago (they already apparently stabilized and ceased ~2 years ago, long before this defect started). Windows updates are always current. The notebook model code is 15-BL1XX, more specific id I found was 15-BL100-CTO; SKU 1VW22AV; bought in 2018 from HP directly as customizable (the current Spectre x360 is a bit different, judging by [dis]assembly vids on YT). The display is 15.6 inch UHD (3840×2160) with touch, HP replacement p/n 911082-001. Primary video is Intel UHD Graphics 620, on CPU package, which is i7-8550U. And I even managed to never spill coffee on it or drop it. I dust the cooling air path regularly, with a correct air pressure, so it's been handled gently during all its nearly 4 year life.

 

[atonement]

Have you checked if the issues persist or not with an external monitor connected? Also the integrated Intel GPU is unlikely to go bad. It seems your laptop has an Nvidia MX150. If that's correct does it happen more commonly in case of apps like Photoshop that should leverage the Nvidia GPU?

 

[Cy_kkm]

I thought about it. The notebook has an HDMI port. But what info would I get from this exercise? The driver circuits for the eDP panel and HDMI are separate. I'll give it a try, but chances of the issue reproducing on an external display are practically nil.

The issue persists over power cycling, during boot, so I would not blame it on any software or drivers. All it takes is to warm it up. This kinda points to the mobo. The backlight PWM control is also on the CPU/GPU, but I don't really know if it drives all displays directly, or requires additional buffer/driver ICs.

I found a spot on the case where a good tap with a rubber mallet stops the mayhem on the screen at once, but that also proves nothing, it shakes the display too. The minimum brightness at which the problem starts goes higher day by day. I currently cannot set to less than half the full brightness, and without the help of the mallet, it's no longer stopping by itself.

Luckily, I found a Lenovo 1 in 2, very similar, that has everything I need, at Costco, and ordered it at once. Too bad the HP thing did not last full 4 years, but it developed a few display problems after a year. The backlight momentarily flashed to full brightness, not often, maybe once a day. Later, it started freezing when the display turned off on timeout, so I had it always on on AC. Luckily, hibernation worked, so I could use it on battery. Probably an assembly defect, maybe some BGA solder joints on the CPU did not flow well. I'll take it apart when I'll have transferred everything to the new one. Maybe it's repairable, if there is any circuitry between the CPU and display. If there isn't any, I'm totally not up to X-ray‐inspection of the CPU BGA joints and resoldering it, too much trouble. Maybe I'll cook it in foil in the toaster oven from room temp to 220°C as a last resort—it has a surprisingly good thermal profile for SMT soldering—but won't spend any more effort on reviving it.