A2681 MacBook Air 13" Short on board question.

[Stephen]

The board turned on before hand but it was liquid damaged, I was able to fix some of the issue with the board, but the battery wasn't charging and so we replaced a few caps and still no luck, swapped out 4 batteries to see if the batteries were bad, and they were all good batteries after final testing. I checked for voltage at PPBUS_AON and no voltage was present which was odd, so I went ahead and replaced U5200 with a new chip since this has something to do with the charging issue and power issue. Replaced but no life still, so went ahead and look for shorts and found an odd area that is shorted to ground.

Cap C83B1 is shorted to ground and all the caps on that area, so the caps are not blown, the area in question is PP1V05_S2SW_VDD2H. This is showing up connected to the CPU and I am hoping it is not a failed CPU. Also I did not inject voltage more than 1 Volt into the board to find any shorts on PPBUS_AON but no shorts showed up. I am getting 5Volts and 0.06amps. So what I am confused as what could be the issue? Board looks fine, but I am leaning towards the CPU is failed. This could explain a lot more issues why the battery wasn't charging after replacing the caps that were faulty but donor caps. Board did turn on after we repaired it and now it's dead with a different issue. Any help would be appreciated.

[mon2]

What is the resistance to ground of PPBUS_AON?

Remove F5200 and then test the voltage to ground of PPBUS_AON again (ISL side).

[Stephen]

4.00 M ohms and dropping

[mon2]

Good. Check the resistance across C5220 (with no power).

[Stephen]

Both Sides of C5220
9 M ohms and dropping.

[mon2]

No, check with both probes across C5220. Interested in the full current path resistance of the input side. piernov noted in one post that this is a common fault area.

[Stephen]

Apologies. 3.2 OHMS

[mon2]

Also, yes, you are chasing a different rabbit hole now. Earlier, the fault may be the same as what a number of techs have faced about a week ago. After replacing the LCD display, this laptop was unable to charge the battery across 3 units. LCD assemblies from different vendors (XJS & Seven Puppy).

Do you recall if the laptop was able to power up with only the battery? That puzzle is still being solved. Master Liu noted that he swaps out only the defective LCD with an original LCD from the same model - does not swap out the whole display assembly. That solution works.

Has this laptop had the LCD assembly replaced?

Review the notes in the schematic on page 24 as follows:

[mon2]

3.2 ohms

It may be too high. Can you short your meter probes? What is the baseline for your meter for '0 ohms'? This measurement should be 1+1 = 2 ohms.

[Stephen]

Also, yes, you are chasing a different rabbit hole now. Earlier, the fault may be the same as what a number of techs have faced about a week ago. After replacing the LCD display, this laptop was unable to charge the battery across 3 units. LCD assemblies from different vendors (XJS & Seven Puppy).

Do you recall if the laptop was able to power up with only the battery? That puzzle is still being solved. Master Liu noted that he swaps out only the defective LCD with an original LCD from the same model - does not swap out the whole display assembly. That solution works.

Has this laptop had the LCD assembly replaced?

Review the notes in the schematic on page 24 as follows:

Previously, the client came in with liquid damage, I found a lot of shorts on the battery area that needed to be replaced, now those shorts are gone, the screen did turn on before hand and the screen has never been replaced since this is the first time its being worked on. LCD has never been removed or changed so it is the original LCD.

The laptop would only power on with power connected, battery would display charging at 1% but never increasing and instantly dying when unplugging power, now the board doesn't turn on anymore. Complicated board I tell you!

[Stephen]

It may be too high. Can you short your meter probes? What is the baseline for your meter for '0 ohms'? This measurement should be 1+1 = 2 ohms.

I do recall the ohms dropping on that line. It did go below 3.0 ohms and steadily dropping across both points. Let me check again

UPDATE: ohms dropped to 2.2 steady now.

[mon2]

Which chip was used to replace U5200?

Was it sourced from a donor board ?

[Stephen]

489900A6 BGA Power IC Chip

this was the exact chip we sourced. Matching

[Stephen]

Any thoughts Mon?

[mon2]

What is the exact voltage to ground of PPBUS_AON? 0 volts?

Also interested in the voltage to ground for:

PPDCIN_AON_CHGR
PPCHGR_VDDA
PPCHGR_VDDP
CHGR_PHASE1_1
CHGR_PHASE2
PPVBAT_AON_CHGR_REG

[Stephen]

Hello,

Going to test these points and update you.

I do know PPBUS_AON is at 0 Volts.

[Stephen]

PPDCIN_AON_CHGR 5.14volts
PPCHGR_VDDA 4.48Volts
PPCHGR_VDDP 4.46Volts
CHGR_PHASE1_1 0 Volts
CHGR_PHASE2 0 Volts
PPVBAT_AON_CHGR_REG 0 Volts

[Stephen]

Update: I found a faulty resistor near U5200. Replaced. Now I am getting 12 volts. Still looking.

[Stephen]

Now I am at 20 Volts. Ok!

[Stephen]

Ok so the computer is turning on but now the batteries show 1% but are not charging. I am back to square one with the battery not charging. The LCD has never been replaced and it is the original LCD. I have replaced a few bad caps on the area that affects the battery but nothing still.