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Mac Air 2012 - A1465 820 3208A

J

jpadie

New member
Hi

I've got another mac air in at the moment Coffee damage. Sugared too.

the whole backlight area is nasty. Fuse blown. I've replaced that and the green light goes nicely to orange. But fan stays at high speed throughout.

No power in the backlight circuit. Looks like there's no signal on LCD_BCKLT_EN but there is 8v on LCD_BCKLT_EN_L on Q9707. Is that normal?

some of the coils appear shorted to ground - L7100, L7720 and L7630 and every other coil towards the fan; and U1800 is getting hot to touch. all are at about 45C.

any thoughts on chasing down the short? alcohol test does not show anything particularly hotter than other things. likewise an infrared heat scan (with a gun).

thanks
Justin
 
A

aprendiz

Moderator
You have a display connected??
What is the resistance to ground on L7720?
Fan at high speed is a sensor failure, also if trackpad is not connected....
 
J

jpadie

New member
thanks aprendiz

resistance to ground over L7720 is approx. 13MOhm.

no display connected. Board is bare, so no keyboard, trackpad etc.
 
J

jpadie

New member
just following up on this. the laptop continues to power up but a couple of power rails seem odd. notably

PP18v5 is at 14.8v rather than the stated 18.5v (this feels like an error in the schematic...) ; and
PPVRTC_G3H is at 3.3v rather than 3v.
PPVCore_S0_CPU is at 0.8v rather than 1.25 and
PPVCORE_S0_AXG is also at 0.8v rather than 1.05.

I poured some mild heat on to U1800 and the coil resistances are now:

L7630 16Ohm

L7330 820 Ohm

L7110 20 Ohm

L7510 5Ohm
L7550 4Ohm

Any hints on where to search next?

many thanks
Justin
 
D

dukefawks

Administrator
U1800 normally gets quite warm, but you should be able to keep your finger on it.

LCD connector needs to be replaced now and also the LCD cable. This is the reason why you use a cracked trash LCD for testing.
 
J

jpadie

New member
LCD connector is removed. I'm waiting for new connectors so can't test with a different screen yet.

But the voltages on ppvcore still seem wrong . I've removed some of the coils and injected voltage into that rail directly but nothing gets hot.

​​​​​​
 
D

dukefawks

Administrator
This thing was turning on with an image and you are injecting voltage on CPU Vcore? :(

Does it even still chime now?
 
J

jpadie

New member
No idea about the image . The display connector was fubar.

Chiming normally. But low voltages on the 1.25 and 1.05 rails. High voltage on the 3v rail and top speed fan.

I've put it to the side until the connectors arrive . Loads of public holidays in France at the moment so deliveries are few are sparse .
 
D

dukefawks

Administrator
It chimes so board is fine. Replace LCD connector and LCD cable. If you insert the fried LCD cable it will burn your connector again.
This is why you need a cracked LCD for testing this stuff.
 
J

jpadie

New member
Thanks

I've got a few screens now .

​​​​ fingers crossed that connectors will arrive early in the week .
 
J

jpadie

New member
replaced the lcd connector and plugged the fan etc back in. Spun up the first time then stopped and now will no longer spin.

U1900 still getting very hot to touch. not something I'd like to keep my finger on (and hotter than comparable machines).

Gut feel is that there is still a short somewhere in this board but nothing is getting hot other than U1900.

Any ideas?

thanks
Justin
 
J

jpadie

New member
yes U1800 gets hot without fan spin.

the fan 'jolts'. rocks on its spindle.

there is voltage on the fan pins though. is this a case of a broken fan ?!!
 
J

jpadie

New member
nope. nothing on PPVCORE.

14.4v on PPDCIN_G3H.

the other rails are mostly there but:

I'm not getting 1.8v at all the points that it should be present. for example - there is nothing at R2719 but u2700 is fully provided.

PP1V5_S3: 1.35v
PP1V5_S3RS0; 1.35v (but PP1V5_S0: 1.5v)
PPVTTDDR_S3 : 0.675v
PP0V75_S0_DDRVTT: 0v
PPVCCSA_SO_CPU: 39mV
PP1v05_S0: 76mV
PP1V05_S0_LDO: 1.05v
PPVCORE_S0_CPU and AXG: 0v
PP1V5_S3_CPU_VCCDQ: 1.35v
PP1V05_S0_CPU_VCCPQE: 0v
PP1V8_S0_CPU_VCCPLL_R: 1.8v

If I've not included a rail then it is reading OK. I have not checked the TBT rails.
 
J

jpadie

New member
the 1v8 issue was measurement error. It is present (1.78 - 1.80) in all the right places. ​

I had some spare time so probed some of the main caps around the coils. C1768, c1680, c1683 and c1682 (PPVCore caps) all have very low resistance (4-15Ohms). I'll have to chase this through.​
 
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