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[SOLVED]820-3787 questionmark folder, no wifi

P

PJs

New member
Hello,

I've got here 820-3787 that turns on to a questionmark folder with known good drives (with High Sierra installed and running on different machine). It will also not find any wifi network in boot selection menu. USB is fully functional.

I bought this machine with no video issue, but that was just L8300 killed by bad LVDS cable - after changing those two things, it worked well. However the screen was in bad shape, so I ordered a new one. After changing the screen it stopped booting from SSD (just questionmark folder, even with known good drives), so I tried to do an internet recovery, but that immediately gave me 1005F error (even after PRAM/SMC reset), so the wifi also doesn't work. I think it's a PCIe issue, probably caused by bad camera in that new screen assembly. However I also changed SSD at once with the screen and the resistance measurements on camera connector are the same as on known working one, so I'm not certain what caused this issue and if the camera is really defective. The board looks pristine, no spills, oxidation, missing parts, signs of previous repairs or anything like that. I only found a little solder ball next to U3711, so I changed it just to be sure, but that did not solve anything. I also changed U1900, no progress.

I've got here another A1398 with 820-3787 that is fully working, so I can compare my measurements.

All the rails are present and stable, including these:

PP1V8_CAM
PP1V35_CAM
PP1V2_CAM
PP3V3_S3RS0_CAMERA
PP3V3_WLAN
PP3V3_S0SW_SSD_FLT

CAM_PCIE_RESET_L
TBT_PCIE_RESET_L

AP_CLKREQ_Q_L
SSD_CLKREQ_L

CAM_CLKREQ_L is low, but that should appear after successful boot to OS according to the other machine (?)

These components are not shorted and looks pristine:

CAM
C4030 - C4033
C4061
C4062

AP
L3501
SSD
C3710 - C3717

TBT
C2800 - C2807
C2840 - C2847

I've already seen this issue on different 3787/3662, but there was always some bad cap... on this one I don't know what else to look for :(

Thank you
 
2informaticos

2informaticos

Administrator
Staff member
"All the rails are present and stable, including these:
AP_CLKREQ_Q_L
SSD_CLKREQ_L"
If you mean 3V, that's bad.
"L" at the end means signal active low (0V).
As these are clock request signals, should be activated.
3V means disable signal in this case...
 
P

PJs

New member
Yes, I mean those two are high (3V), not low. But what can cause this? I cannot find almost anything about those CLKREQ_L signals...
 
P

PJs

New member
U3740 with good SSD drive connected:

1. 3.42V - PP3V42_G3H
2. 1.00V - P3V3SSD_VMON
3. 3.31V - SSD_RESET_L
4. 3.42V - SSD_RESET_CONN_L
5. 0.00V - GND
6. 3.28V - SSD_PWR_FET_EN
7. 0.00V - SSD_CLKREQ_CONN_L
8. 0.00V - SSD_CLKREQ_L

So I guess connecting the SSD probably solves that "mystery" with CLKREQ_L being high :))
 
D

dukefawks

Administrator
2. 1.00V - P3V3SSD_VMON

Sounds like the culprit...

And why do you think that should be anything else? Did you even look at the diagram before giving bad advice?


I don't see how a bad camera could mess up the PCI really. At this point I really have no idea what this could be. Bring out the scope and see if there is a PCI clock signal present.
 
P

PJs

New member
No Title

OK, got an oscilloscope. Never worked with one, but on a working machine if I measure PCIE_CLK100M_SSD_P or N, the curve and spikes looks the same as on the working machine.
 

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P

PJs

New member
This is really quite confusing for me. I cannot boot from USB->SATA SSD with High Sierra (the other A1398 2014 boots with it, but this one does not even see it), but I can boot from USB flash drive with High Sierra installer, and when I do that, the wifi is working there, and also the disk utility correctly see the internal SSD drive. So why the hell it does not boot from it, is this possibly a BIOS issue? Sorry I know you also asked about camera, but I did not find a way to test it yet, as I can only boot to that macOS installer.
 
Last edited:
D

dukefawks

Administrator
You need to install 10.11 from USB and update from there to run the APFS EFI update.
WiFi not working in boot menu is usually cause the wrong model year wifi card is in there and the EFI has no driver for it. In OSX it will work normally.
 
P

PJs

New member
I feel so lame right now :D. You're right, it works now. I did not realize that I swapped wifi card with the screen assembly and it's from L2013 while the board is M2014. It works again with the original M2014 card. Also I sold the original SSD before the new LCD came to me and there was El Capitan installed, while all the drives I tested had High Sierra with APFS.

It's unbelieveable that you were able to solve it with so much misleading informations. Thank you!
 
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