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820-01958-A No Power 5V and 0.10a current draw

C

CRC2018

Member
Just got an 820-01958-A in symptoms are stuck at 5V on USB-C Meter, no signs of life and 0.10a current draw.

Visual inspection reveals:
Damaged flex cable between audio board and main board
No visible corrosion or water damage present.

Device is not visible when connected to another mac with Apple Configurator 2 and it will not go into forced DFU mode either.
From the voltage sequence PP3V3_G3H_RTC is present but P5G3S_EN is missing. Sleep and Awake voltages all appear present and not cycling.

No shorts present on the PP5V_G3S line.

I'm thinking likely dead T2 chip - perhaps something shorted across with the damage to the audio board flex? Any other thoughts?
 
C

CRC2018

Member
Think I might be getting somewhere with this one, comparing with another board I found PP1V8_G3S is showing a 40ohm resistance to ground so not fully shorted but certainly abnormal. The problem is however even if I inject the full 1.8v into PP1V8_G3S I get no current draw and nothing visibly heating under thermal cam. I've spent some time probing around the IC's which are connected to PP1V8_G3S to try and ascertain whether one of them is causing this but have come up blank. Are there any common IC's that would cause a short/problem on PP1V8_G3S before I start pulling all of them off to try and clear this issue?
 
C

CRC2018

Member
Well Audio Amp out U6400 - no change. Basically then went through the process of removing and reinstalling every other part on PP1V8_G3S until I got to the Wifi IC, After removing this the low ohms reading on PP1V8_G3s is gone and it's now reading 3Kohm.

Unfortunately this hasn't changed the behaviour of the board - it continues to stick at 5v and 0.10a current draw and is also not visible in DFU Mode.

Would it start up without the Wifi IC or is that now the reason it's not starting? Can I just swap the IC off a donor board or is something else needed?
 
C

CRC2018

Member
1v8_G3s is still missing but no longer shorted. I also took U6400 off again just to confirm that wasn't affecting anything but it hasn't changed anything!
 
C

CRC2018

Member
No the other G3s voltages are still not present - PP5v_G3s is reading a tiny amount around 0.03V and its enable signal P5G3S_EN is still missing. I did try it once more with the charger and thermal camera and i'm seeing a tiny amount of heat from U4850 - we're talking board is 16C and this IC is 19C.

Also might be nothing but missing P3V3MAIN_PGOOD - although R7601 measures good at 100k and there is 3.3v on one side of it!
P3V_G3H is present and correct at 3V.
 
Last edited:
C

CRC2018

Member
Right so with Pin 20 isolated (made a small cut on the trace going to the test point) P3V3MAIN_PGOOD is present. Would this mean bad U7650?
 
2informaticos

2informaticos

Administrator
Staff member
You can try changing it.
If 3V3_G3H has correct voltage (+/-10%), then U7650 should release PGOOD2 signal.
 
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