A1708 820-00840 no PPBUS, no short

Narek

Member
As it's my first post on this forum I want to say hello to all members!

I'm fighting with a kind of odd case of A1708, board number 820-00840. Board looks perfectly clean, untouched, no water signs, no damages, even no dust on it. Customer claims, that computer just turned off by itself and stopped charging.

First measurements:

- no 20v on charger, stuck at 5v
- PP3V3_G3H 2,5v (no short, 0,337v in diode mode)
- PPBUS_G3H 0,115v (no short, 0,386v in diode mode)

I've noticed U6990 and SMC were getting hot (SMC was warmer), so replaced U6990 first. No results, PP3V3_G3H still at 2,5v. Later I've replaced SMC from the same board which has brought PP3V3_G3H back to 3,3v, U6990 not getting hot anymore too. Board switched to 20v 0,039A on charger, but still not powering on. Weirdly, when I was heating up the area around SMC, the PPBUS_G3H raised to 13v and board booted taking around 1A. After connecting screen I had logo with progress bar, but before it loaded fully, board cooled down and turned off. I thought it's just bad soldering, so I pulled SMC, reballed and put it back. No changes, but this time it takes much longer for board to swicth to 20v or sometimes it stays at 5v 0,05A. Now heating SMC area doesn't make it to "boot" like before. When it takes 20v anyway there is no PPBUS.

- Here are basic voltages I'm getting (diod modes in brackets)

- PP3V3_G3H - 3,3v (0,334)
- PP20V_USBC_XA/XB - 20v or sometimes stuck at 5v (0,158)
- PP3V3_UPC_XA/XB - 3,3v
- PPBUS G3H - 0,037v (0,385)
- PP3V3_S5/PP5V_S5 - 0v obviously, there is no PPBUS (0,345/0,398)

- readings around D6905 (I've replaced it just in case):

pin 1 - 20v (0,381)
pin 2 - 0,037v (0,515)
pin 3 - 20v (0,510)

R6905: both sides reads 0,037v, resistance OK.

- U7000 replaced twice, here are readings around:

PPVIN_G3H_P3V3H3H - 20v
TBA_CSIR_N - 20v
TBA_CSIR_P - 20v
TBA_COMP - 1,15v
TBA_LX1 - 0v
TBA_BOOT1 - 4,86v
TBA_VDDP - 5,15v
TBA_VDDP - 5,15v
TBA_BOOT2 - 4,92v

current sense:

TBA_CSIR_P/TBA_CSIR_N - 2,5ohm
TBA_CSOR_P/TBA_CSOR_N - 2,7ohm

other readings:

TBA_HPWR_EN_L - 3,38v (resistance OK)
BUF_SMC_RESET_L - 3,40v
PP3V3_S5_SMC_VDDA - 3,4v
SMC_WAKE_L - 3,1v (shold be low, right?)
PP1V2_S5_SMC_VDDC - 1,20v
PP3V0_S5_AVREF_SMC - 3,0v


All resistors around SMC checked, nothing is missing, values are correct. Voltages at U6100 not present, but I think it's because PPBUS is missing. Do you have any suggestions? Can it be bad SMC again?
 

2informaticos

Administrator
Staff member
First of all, welcome to the forum!

Seems that something else reacted to the heat applied when changing SMC.
Could be CPU, as is close too.
Check first for moved components.

You can try other SMC/U7000...
 

Narek

Member
Ok, I will replace U7000 again, as for SMC I have to order new one as I’m actually out of them. The interesting thing is, when the board is stuck at 5v it’s enough to delicately press the SMC and voltage gets up to 20v and stays like that. I’ve reflowed SMC, but with no changes. Maybe there is structural damage in SMC? Or broken trace in pcb?
 

2informaticos

Administrator
Staff member
Could be broken trace, or bad solder.
Only get such reaction pressing on SMC, not in other board area?
 

Narek

Member
Yes, only pressing directly on SMC. I’ve checked other side of the board under SMC, all resistors there are well soldered and measure correct values. I’ve replaced U7000 as you have advised, PPBUS still at ~ 0,04v.
 

Narek

Member
Sure, I will keep you updated. Thank you for support!

I have one more question. I was curious if EFI hasn’t got corrupted and after putting dump in ME Analyser I got such message (picture in attachment). I’ve never got such message. Is it normal for newer EFI, or should I clean ME region/take “new” clean dump and reflash the chip?
 

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2informaticos

Administrator
Staff member
ME Analyser doesn't recognize that ME properly, maybe.
Don't touch BIOS yet.
Get Medusa programmer, if you want to stay in business with Apple repair.
 

Narek

Member
I'm considering buying it for some time already, but honestly even my actual programmer isn't in use most of the time, maybe 1-2 times in a month. But of course medusa saves time, possible mistake risk and unnecessary board heating cycle. Anyway your suggestion made it jump higher in my tools-to-buy list ?
 

2informaticos

Administrator
Staff member
Medusa has the big advantage to properly clean ME region, not like other f***g Internet softwares which only replace ME without configure it.
And has more features needed for Apple repairs...
 

Narek

Member
@2informaticos today my donor boards got delivered, I've changed SMC along with U1900 and the results are: it turns on 20v right after I connect charger (previously I had to wait a while), but it's stuck at 0,45A. Also, what's good news I already have steady 13v on PPBUS. After connecting trackpad it clicks, but have no image on display, no USB activity.
 
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Narek

Member
Checked again, it's stable. I plug the charger in, it switches to 20v and from this moment CPU VCORE goes up to 0,959v and stays like this. I kept measuring it for 1 minute, it's not changing at all.
 

Narek

Member
Not yet, I don’t actually have known good one (only original and one with came with donor board). I will need to search for it, or if you have it and will be so kind, I will be grateful for sharing it with me.
 

Narek

Member
Reflashing EFI did the trick, computer starts now, loads system. Now I have 2 other problems:

- I've changed the fsys region in bios you sent me with the original bios fsys (I've copied everything from this region) but S/N doesn't show up in "this mac" info, also when I want to run diagnostics it shows me, that mac doesn't have S/N, and I can't perform diagnostics.

- keyboard doesn't work at all. With external keyboard it works fine, but internal doesn't react even for power button. Can it be related to bad SMC or bad soldering? I don't have another keyboard or topcase to replace it.

EDIT: I've edited bios you sent me and replaced S/N only. Now diagnostics works, S/N is visible in "this mac", also keyboard works perfectly. I think without S/N board wasn't able to identify itself and that's why keyboard was off.

Computer is repaired, @2informaticos, as always thank you for support! If not damaged SMC which I have used for the first time it would be repaired earlier. What to do, in such market situation sometimes we have to cope with damaged components from donor boards...
 
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