830-3437 - Orange Light, VCore present, Fan spin, SPI Working --> no Chime & Video

[smiba]

830-3437 - Orange Light, VCore present, Fan spin, SPI Working --> no Chime & Video

I really hope this isn't one of those embarrassing issues where I just overlooked something haha

Anyways, this macbook Air was water damaged and already bought to another company who told "they would need to replace the motherboard as it can't be repaired", I did not notice a lot of corrosion but I did notice some rusty parts and blackness/discolouration on the two backlight power pins of the display connector. (And a blown F7700, it no longer blows after replacement though).

When you plug in the charger it becomes green for about one second, before it turns Orange. (No battery inserted). The CPU fan will switch on/off for about 3-4 times for about 4 seconds until it keeps on spinning. There is no Chime
System responds to pressing the power button and shuts down by keeping it pressed or starts by pressing it just once.

CPU Vcore is 1.75V, the CPU gets warm after keeping it on for a while.

All major power lines are available and at their voltages, SPI chip has both Input and Output communication (Seen with oscilloscope)

When plugging in the battery PPBUS_G3H drops from 8.8V to 6.8V, I don't think this is intended. System does not run off battery, although the battery might just be empty. Possible issue in the power circuit?

No backlight (BKLT_PLT_RST_L signal is Low. The pins on Q7706 look awful but the chip responds as expected. Pin 3&4 (Gate & Source) are about the same voltage), No Keyboard backlight etc.

A lot of the components positive power pin(s) look slightly bad, but this is probably because corrosion usually starts on the positive terminal. Power still goes through them properly and the solder connections are not broken.

Summery:
CPU Vcore = 1.75V
SPI Chip I/O activity
Doesn't run off battery, when having a battery plugged in PPBUS_G3H drops from 8.8V to ~6.8V
No backlight, the FET isn't opened (No power out on PPVIN_S0SW_LCDBKLT_FET)
Fan spins
Orange Light on charger, battery or not
No Chime
F7700 Backlight fuse was blown, replaced and its no longer blowing.

If anyone can help me, thanks a lot!

 

[aprendiz]

Turning on and off when you plug in charger without battery is normal....
If you connect an USB mouse, does it shows activity????
Caps Lock key works??
Have you tried with another display assembly??
Fuse blown was for a reason, maybe bad cable or display....

 

[smiba]

Turning on and off when you plug in charger without battery is normal....

Obviously

If you connect an USB mouse, does it shows activity????
Caps Lock key works??.

No and No, For this the system would need to be past POST to work. However since there is no Chime its to be assumed the system does not boot or get past his early bootup stage.
USB Mouse doesn't light up either

Have you tried with another display assembly??

Nope, but the backlight pins on the display are 0V and the FET is not opening so the backlight is completely not being powered.

Fuse blown was for a reason, maybe bad cable or display....

I assume the fuse was blown due the huge amount of whatever the person was drinking ended up on the motherboard, the backlight area looks the worst of all with some pins so rusty they barely would stick to the solder without extensive cleaning. Right now the backlight isn't even being enabled so the current going through the fuse is very minimal, but there is no short on the backlight lines which tells me the fuse would most likely not break.

It is possible that the display is permanently damaged due the short though, but that would still leave voltage on the backlight pins with the screen disconnected.


This all is if I'm correct though, feel free to let me know if I'm being stupid

 

[dukefawks]

The 3 times on/off does suggest that the system is running POST to some extent. Check corrosion around U6100, especially the resistors to the SMC R6114-17.
Of course USB mouse should light up first before we can continue with backlight issues.
Orange light without battery is normal.
Voltage drops to 6.8V because your battery is very empty and needs to charge.

 

[smiba]

For the next time, do all macbook Air's have this orange light behaviour or just a select few? I know macbook Pro's don't behave this way.
I'll definitely remember for next time!

I checked Resistors R6114-17 and they all measure within 1% of their specification.

U6100 shows close to no signs of any corrosion, all the pins are looking nice

Could U2800 be causing issues? Since its located right in the middle of the corrosion war-zone?

 

[dukefawks]

All 2012+ machines do the orange light thing.
What does U2800 thunderbolt have to do with the machine working?
This could be anything, corrosion under SMC maybe. Corrosion under any chip could cause this really.

 

[smiba]

After checking the schematic for the pins of U2800 I'm highly sceptical it could prevent the system from posting, you're right.

I'll try to reflow one chip at a time to see if that fixes anything. I know its not a proper fix and I agree, but it at least would tell me what chip I need to reball

Thanks for your help, if I solve it I'll post to this thread. Otherwise I sadly have to accept not everything can be fixed