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SOLVED: 820-01700 fixed after LD but throttling(?) now

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captainmac

Member
Haven't got too much experience with this board, so bear with me.
This board came in as no power after some liquid damage to the middle portion of the board (i don't see this often as liquid usually hits the 'wings' on these boards). No Corrosion on the CPU/GPU Area luckily, but only on the backside of the board, concentrated mostly around UA600and U9801

There was a problem with RA602 being blown, which i think prevented the board from posting. After cleaning up corrosion in that area, reflowing U9801 mostly, and replacing the resistor RA602, the board boots.
However it's terribly slow.
There is no higher than normal fan-activity, and HWMonitor doesnt report anything strange i think. (it reports 129C on CPU Core 8, but thats weird because this machine is a 6-core cpu) see attached photo for all sensors.

I think it is being throttled, I cannot really verify with Intel Power Gadget, because that won't run on this newer macos (can't activate it's kext)

If i measure around U4800 circuitry, i get SMC_PROCHOT_L signal (what i mean is: the signal is reading close to 0V)
However i dont know what can cause this.

I think the voltage divider for U4800 (R4800 and R4802) is working,

ppbus is 12.6V

voltages of U4801:
pin 1 is 1.99v
pin 3= 1.20v
pin 4 = 3.3V

voltages for U4800 are good, but pin 6 and 12 are low:
pin 1 = 3.3v
pin 2 = 3.3v
pin 4 = 3.3v
pin 6 = 0v
pin 9 = 3.3v
pin 10 = 1.2v
pin 12 = 0v

Dont know exactly how this circuitry should work, need a little help, thanks in advance!
 

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2informaticos

2informaticos

Administrator
Staff member
Different models have the same SMC_PROCHOT_L signal.
Don't you have any other working MacBook?

Did you test removing R7102?
U7100 may be the one pulling down the signal.
 
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captainmac

Member
Just realised i do have more of these machines in now..
Have checked on a fully working board and the SMC_PROCHOT_L is low there as well, eventhough that machine is not throttled. Guess i'm barking up the wrong tree here.
What can be another reason this thing is so terribly slow?
 
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captainmac

Member
Have tested this board in a fully working chassis as well today, no changes..
OK, so out of desperation i backed up all the data first and have done a DFU Restore. The process went pretty normal, however when reinstalling via Internet Recovery it is painfully slow (i suspect the same throttling is happening now) and errors out at the end with 2003f error.
Have done restore multiple times but cannot reinstall macos for some reason.
I suspect i still have the throttling issue which i guess i need to fix first.. any pointers greatly appreciated.
 
2informaticos

2informaticos

Administrator
Staff member
There may be a GPU problem.
Start the machine in Diagnostic mode; lets see if any error pops up.
Put the machine in Target Disk mode and check its SSD from other machine.
Next, try to install original macOS; start with Shift + Option + Command + R.

If still the same, change security settings accordingly and try booting Windows, or Linux Live.
You may also try installing Windows 10.
 
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captainmac

Member
OK, tried to do as you suggested:

Machine wont start in Diagnostic, when holding D at startup, it wants me to connect to WiFi and then says Starting Internet Recovery for longer than an hour, ending up on error -2003F
It does the same when i try to boot it using ShiftOptionCmd-R, same when booting Live Ubuntu stick.

I have tried Target mode again, SSD shows us unitinitialized in Diskutil (probably because it was erased as part of the DFU Restore), but i am able to reformat it, and ran firstaid without issues.

Your last suggestion is to change security settings, but i cannot, since i can't even access a Recovery partition. (now i'm slapping my head, because i maybe shouldn't have done a DFU Restore )
 
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2informaticos

2informaticos

Administrator
Staff member
Apple claims that DFU restore is to fix problems, not to brick your machine.
But you are not the first who went in problems in this way.

Try to restore via ethernet, instead of wirelesss; some peoples said that fixed 2003F error.
Just in case, try DFU after flashing SoC ROM (U4770); don't forget to make backup first.
 
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captainmac

Member
God I fucking hate T2-boards..
Today I’ve replaced ua600 because it still looked dodgy. Ultrasoniced it afterwards and still this thing is slow as hell, did dfu restore twice, all to no avail…
Will check in here tomorrow, I also found online while googling that these -2003F errors seem to be related to network settings, but I never have issues with this network and dfu restores..
On another note, the boot-menu screen sometimes shows weird graphical artifacts; kind of hard te describe I’ll see if I can take a photo tomorrow. Leaning also towards the gpu being toast. But shouldn’t this thing boot up with its integrated gpu during boot sequence and hence have no issues if the dGPU is fucked?
Talk tomorrow…
 
2informaticos

2informaticos

Administrator
Staff member
Remember the old 2915 board, where the grapchis artifacts appeared in boot menu.
There the dedicated GPU was enabled by default; unless changing BIOS.
I suppose same thing is valid here; but no way to modify the BIOS.
 
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captainmac

Member
OK, so i have tried flashing U4770 with a new ROM Dump i found on one of your other posts ( https://boards.rossmanngroup.com/threads/a2141-820-01700-05-no-power.63469/#post-95679 )
With this rom dump flashed, i cannot complete a DFU Restore, it hangs and says takes too long to transfer from DFU to DFU state (something like that).
I am wondering if this is because this dump was from a 820-01700-05 board and I have a 820-01700-A board?

Do you happen to have a SoC Rom dump for the A-version?
 
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captainmac

Member
OK some good news: and a little info on what i found, it might be of help to others later on:

After i put back original U4770 dump and tried DFU again, it was still painfully slow. I managed to boot it into Internet Recovery with the help of an ethernet-cable (progress) but still extremely slow.

After that i decided to take a look at the photos i made when i took it apart the first time, and noticed I never really paid attention to the tiny blue smudge on an area around U8250
After measuring around, i noticed i don't have PP3V3_G3SSW_SNS coming out of U8250
Decided to check under U8250 and sure enough,found that the pad #2 for PP3v3_G3H_T was burnt out!
I rebuilt that using some wire and replaced U8250
Got PP3V3_G3SSW_SNS back, as i understand it, it powers a lot Current Sense ICs which in turn talk to the PMU, so it makes sense that this thing was throttled i guess? What is strang is that the machine booted normally and the fans were spinning normally? Also no odd readings in HWMonitor?

Maybe someone with more understanding can explain this better.
Anyways, thanks for the help so far, and I'm glad i get to make money off of this thing, it's taken way too much of my time!
 
2informaticos

2informaticos

Administrator
Staff member
The fans spin to max if thermal sensor is triggered.
You had problems with Isense sensors instead.
HWMonitor could discover such problem...
 
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