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MacBook Pro 16 2021 820-02100

isa1985

isa1985

Member
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

2informaticos

Administrator
Staff member
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

isa1985

Member
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

2informaticos

Administrator
Staff member
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

isa1985

Member
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
 
isa1985

isa1985

Member
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.
 
2informaticos

2informaticos

Administrator
Staff member
If you really inject correctly into PPVOUT_LUXE, then RP803/9 can only heat if you have problems with UP800 and QP800-3 at same time.
 
isa1985

isa1985

Member
RP809 and RP803 heat up when I apply power to LUXE_ISL_R_P. Today, I will remove RP809 and RP803 to see if the short circuit disappears.
 
2informaticos

2informaticos

Administrator
Staff member
Why woukd you want to apply voltage there?
Injecting voltage into ground???

Open your eyes when you look to a schematic; try to understand it.
If you can't, ask before making more damage on the board; or your PSU.
 
isa1985

isa1985

Member
As I mentioned at the very beginning, LUXE_AGND, LUXE_ISL_R_P, LUXE_ISL_R_N, and GND are shorted together. I don't want to make any mistakes, and I'm very grateful for your help. I've now soldered UP800, so please let me know how I should proceed. I have a thermal camera to find out where things are getting hot on the board. Is it safe to connect the power supply with 1V to LUXE_AGND, LUXE_ISL_R_P, and LUXE_ISL_R_N?
 
2informaticos

2informaticos

Administrator
Staff member
"What is resistance to ground at PPVOUT_LUXE (w/ and w/o screen connected)?
-----------------------
Without the display, it’s 0.00 Ohms"
???
 
2informaticos

2informaticos

Administrator
Staff member
Why to check with screen, if already have short without it?
However, the problem is that we talked about PPVOUT_LUXE and you ended injecting voltage on totally different point, CONNECTED to ground!!!
 
isa1985

isa1985

Member
I found the problem; it was the JP900 LCD connector. I cleaned it, and now when I measure resistance to ground with and without the LCD, it starts at 550 kOhms and keeps increasing endlessly.
I also tried with another multimeter and got the same result.
 
isa1985

isa1985

Member
I'm glad to hear from you, as I thought you probably didn't want to hear from me anymore. No, the backlight is still not working.
 
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