MacBook Pro 16 2021 820-02100

[isa1985]

I have a MacBook Pro 16 (2021) with board number 820-02100. Two weeks ago, I replaced the display and the backlight IC. Now the device has come back, and there's no backlight again. I’ve replaced the backlight IC two more times, but it didn’t solve the problem. So, I started diagnosing and found that the UP800 pins 7, 13, 19, 9, 27, 10, 22, and 12 are shorted together. LUXE_AGND, LUXE_ISL_R_P, LUXE_ISL_R_N, and GND are all shorted together as well. Does anyone have any ideas what this could be?

 

[2informaticos]

As per schematic, all mentioned lines are connected to ground.

I don't spend my time to check UP800 pins on boardview; provide schematic notations for the future.
I usually have 10-20 schematics opened on acrobat reader.
But I use boardviewer for my desk jobs only.

Did you replace UP800 two more times without diagnosing first?
Did you test with another compatible LCD assembly?

What is resistance to ground at PPVOUT_LUXE (w/ and w/o screen connected)?

 

[isa1985]

Last time, I just had to replace UP800, and it worked right away. So I replaced UP800 this time as well. I replaced it a second time because I thought something might have gone wrong, and I really wanted to believe the issue was with UP800. You mentioned I should test the 'resistance to ground,' and I did that. Without the display, it’s 0.00 Ohms, and with the display, it’s 0.02 Ohms. I should mention that UP800 is not soldered at the moment. Should UP800 be soldered during this measurement?

Another thing I wanted to mention is that the UP800s I’ve been using are from eBay. Is quality important here? It’s quite possible that these ICs came from China. Should I look for an original from a defective board? It will be quite difficult, but I’ll give it a try.

 

[2informaticos]

How can you eliminate a short (0.02 ohm is pure short) soldering one more component???
To eliminate a short you MUST remove components.

Important is to find first what component causes the short.
LCD assembly NO, as you have short even without it connected.
I bet one filter capacitor on PPVOUT_LUXE is the culprit.
Start injecting 1V there; set PSU amp limit to max first.
You should note which cap gets hot.

 

[isa1985]

Two components, RP809 and RP803, are heating up. However, there's no heat on the PPVOUT_LUXE line, only at the tip of the PSU

 

[2informaticos]

Increase the voltage slowly.
Use powerful cables; you don't want to heat the cables...

 

[isa1985]

If RP809 and RP803 are heating up significantly, doesn’t that indicate they might be defective? Regarding PPVOUT_LUXE, I’ve also used thicker cables, but there still isn’t any hot spot on the line.