820-00840 20v 0.5a no video

Outofwhack

Member
Customer reported no display but very occasionally a login screen.
No visible corrosion.
Fan spins
Caps key toggles
string of usb flashes (snow edition stick)

ppbus_g3h 13.06v
pp3v3_g3h 3.4v
pp5v_s5 5.1v
pp3v3_s 3.1v
allsys_pwrgd 3.2v

L7210pin2 0.96v then 0.67v cpu core voltage

New screen did not show any video
 

2informaticos

Administrator
Staff member
0.67V at CPU core means the board boots; also confirmed by USB activity and Caps Lock reaction.

Do you get external video?
Any fault history?
 

Outofwhack

Member
I do get external video via USB C but only the Apple logo and a gradually extending time bar that reaches 100% and stops with no further change even after 8 hours.
Re fault history: Customer says he gets black screen mostly but very occasional login screen - not sure if he is referring to start or after login.
 
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2informaticos

Administrator
Staff member
Remove internal SSD and test with USB macOS.
If still the same, then try know good BIOS, clean ME.

¡Be aware, disconnect charger and battery, before touching SSD connector!
 

Outofwhack

Member
After removing SSD it was able to boot from a macOS installer USB but with no drive installed nowhere to install to.
I put SSD drive back and held Option but I don't get any video output on either internal or external.
 

Outofwhack

Member
I don't have one - I knew I should have got one of these for debug.
I have a converter to a NVMe M2 card so I will try an install on that.
 

2informaticos

Administrator
Staff member
Check power rails of SSD connector.
Also check SSD_EN, SSD_CLKREQ_L and SSD_RESET_L signals.
SSD inserted, of course...
 

Outofwhack

Member
I have no other machine at the moment. I am just going to try using your previous suggestion of a 'clean ME' but I didnt know how. I've viewed Piernov's youtube
[which I find quite unclear. e.g. at 6min33 why open flash image tool to then drop a file in it and then exit without saving???] but the section headings of the tool at Flash Image Tool v11.8 is very different than Flash Image Tool v9.6 so its not clear which region I have to extract for insertion into my own BIOS download.
 

2informaticos

Administrator
Staff member
If you are not sure about ME region version, search and use ME Analizer.
Just drag the bin file over it and will show you all you need.
 

Outofwhack

Member
Ive already used ME Analyzer v1.255.0 r226 to examine my logic boards extracted ROM data and I can see the version of ROM is 11.8.
My issue is that Piernov's video at 5min45sec is using the UEFITool to examine a file he downloaded from a Github repos ending .scap that is the latest update for the MacBook hardware version. He navigates from "UEFI Capsule" down the subdirectories to locate and extract the raw area of MeRegionUpdateVolume. When I do this with a file matching my hardware MBP141_0178_B00.fd (A1708 Macbook14,1) I cannot find MeRegionUpdateVolume. Should I just use the area from far earlier MacBook? Im assuming 141 means 14,1
 
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2informaticos

Administrator
Staff member
Well, known good full BIOS, even not clean ME, should help to diagnose.
If is BIOS issue, SSD should appear.
Then you need to clean ME and change serial number; fixing Fsys checksum too.
 

Outofwhack

Member
Just managed to borrow another identical board and borrowed the EFI chip.
It did boot from the SSD and get to login screen first go.
However next few reboots the progress bar sticks at 70% for a long time and didnt proceed even after 15mins wait.
This is the same behaviour that this board gave with the previous EFI chip so I think you will agree its not the EFI after all.
 
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