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820-00165 Macbook Air - Fan Spin - No VIDEO (intermittent condition)

L

LCDR2

Member
HI All,

Macbook air
Sometimes boots normally and functions 100%.

Other times, fan will spin, with no video or chime.

Board looks good with no obvious signs of corrosion.

Not a backlight issue. Will sometimes chime and boot normally. When it does not chime there is no video / backlight.

When it does not boot
- Fan spin 100%
- Draws approx 115 ma on bench power supply
 
L

LCDR2

Member
Not reflowed SMC yet.

I've been working my way through power rails
I have PP1V05 SUS 1.05v
I no NOT have PP1V5 S0 (Zero Volts)

Is this consistent with SMC issue / PLT Reset issue or is this an upstream problem?

Kind regards,

James
 
L

LCDR2

Member
OK I checked all the inputs for U7870 and PP1V5 S0 appeared so maybe never mind. No change in laptop behavior. maybe a misread.
 
L

LCDR2

Member
So unplugged and reconnected battery and charger. Fan now spinning at 100% but drawing 235ma. these random board issues are the most frustrating.
 
L

LCDR2

Member
Ok another update. I was looking over the board again. I found R7612 looked a little off. A bit of corrosion and damage.
I checked voltages on each side as I did board restarted and then restarted with 500ma draw

This seems to control REFIN of u7600. Not sure what REFIN does. Given the intermittent nature of the problem, could this explain things?

Tests as 40k resistance instead of 49k.
 
2informaticos

2informaticos

Administrator
Staff member
Power on sequence must be completed, before PLT_RESET_L comes high.
Be sure to get VCORE and CPU_VCCST_PWRGD.
 
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