820-01521 - MacBook Air Not Booting Black Screen VCore Present

mccafe

Member
Hello guys,

I have a MacBook Air that came in for water damage that does not want to turn on. Customer said keyboard cover was on when water spilled. I opened it up and found almost no corrosion except on some caps.

C78B7, C78B6 traces of corrosion, almost nothing to be concerned for.
Pin 12 of J6700 connector was a little burned, but seems fine
Checked other parts of the board.. nothing.

All VCores show 0.65 - 0.7 volts. Fan spins when CPU gets hot. I am able to turn off and on using power button. Amp meter shows 0.28 - 0.32 amps coming from type C charger with battery connected.

I tried connecting to Apple Configurator 2 for the first time, but my MacBook doesn't seem to see it.

Any advice?
 

2informaticos

Administrator
Staff member
Looks like board boots, did you check USB activity?
Check external video too.
Try disconnecting trackpad, also check SMC_LID signal.
 

mccafe

Member
There doesn't seem to be any USB activity. LED light normally blinks, but not in this case - just a solid light. No display on internal or external.

SMC_LEFT_LID is 0.9 volts and SMC_RIGHT_LID is 0.9 volts.
 

mccafe

Member
Ohh okay, so with J6100/700 disconnected, it goes to 0.9 volts for both sides. With it connected, the normal 1.8 volts. I wasn't really thinking when I measured with/without the connections.

SMC_LID is fine..

Anything to do with T2? What I don't understand is that customer heard a little sizzle when the water went in, but there are barely any liquid traces.
 

mccafe

Member
I can confirm USB activity with USB mouse. I tested it alone on desk as well as all parts connected. I also hear the charger connection noise coming from the computer when plugging in the charging cable. The MacBook is pulling 1 - 1.5 amps from the charger which is a pretty good sign. However, no output to external or internal display.
 

2informaticos

Administrator
Staff member
Intel graphics can be damaged, if no internal/external image at same time.
Any liquid sign around J8500, or backlight area?
 

mccafe

Member
These areas look pristine and has no signs of liquid.

PP5V_G3S = 5.12 volts
PPBUS_HS_CPU = 12.64 volts
CPUCORE_PHASE1 = 0.89 volts
CPUCORE_PHASE2 = 0.75 volts
CPUGT_PHASE2 = 0.64 volts
CPUGT_PHASE1 = 0.70 volts
PVCCIO_PHASE = 0.97 volts
CPUSA_SW_LL = 1.03 volts

Very small traces of corrosion between R2728 / R2729
Very small traces of corrosion around D8100 / D8101

Replaced C78B3, C78B2 because the ends were black on pin 1.

Also pin 12 of the J6700 connector is a little burned.
 
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mccafe

Member
Everything seems to be pointing back to the Intel graphics. Is there anything else that can cause both the internal and external to fail?
 

2informaticos

Administrator
Staff member
Did you check external video disconnecting internal LCD?
Also be sure the HDMI adapter used is good for this machine.
 

mccafe

Member
Yes, I checked with and without internal LCD connected. I used a known good type C -> HDMI adapter. We use a couple of these for other MacBooks - working good.

I found corrosion around C7416 and U7410 that deals with Phase 1 CPU VGT. The cap was a little burned on pin 1.

What is CPUGT_GL1? This shows 0.7 volts (phase 1) and CPUGT_GL2 (phase 2) shows 0 volts.

CPUGT_GL1 = 4.2 volts and CPUGT_GL2 = 0 volts.
 
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mccafe

Member
Pins 12 on U7410 = 0.08 volts, but when I check pin 12 on U7100 this shows 2.4 volts. I think U7410 is bad because when I remove it, both pins are 5 volts.
 

2informaticos

Administrator
Staff member
CPUGT_GLx pins are not connected; so no matters the voltage there.

Pin 12 should have PWM signal; but ONLY when the chip receives that signal.
"Pins 12 on U7410 = 0.08 volts, but when I check pin 12 on U7100 this shows 2.4 volts"
Did you check the continuity?

As you found corrosion signs on graphics area, this should confirm iGPU damage.
You can put quality flux and heat CPU; before trashing the board...
 

mccafe

Member
I retook measurements and found that it goes to 2.4 volts then goes to 0.08 for both pin 12s. Not good.
 
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mccafe

Member
Looks like it would power cycle.. 2.4 volts then 0.08 volts after a few seconds. I think the CPU is screwed.
 
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