Macbook A1466 Dead

[mcplslg123]

Macbook Air A1466
Logic board:820-3437B

Problem: It came as dead-no light at all on magsafe.

Steps taken:On observation under microscope, Found U1900 badly corroded on pin1-2-3-4. Desoldered the Ic, cleaned the tracks and resoldered it. No corrosion anywhere else, no liquid damage. MB started,fan spinned and there was chime,I turned it off & left it on the table overnight.Next morning the mb refuses to start-magsafe remains green(not going orange) and no fan spin. Consumption fluctuating up and down from 0.008A to 0.330A on dc bench supply. Lifted U1900 again and cleaned , resoldered but no joy.

SMC_BC_ACOK:3.3V
U7100-DC-IN-16V
PPVRTC_G3H-3.3V
PPBUS_G3h/PPV3V42_G3H-OK
PP5V_S5-keep pulsing from 1.5V to 5V(PROBLEM)

Resistance on PP5V_S5-45K and on diode mode-OL.

I've replaced U7501 and flashed known good bios with clean me but problem remains.

I dont have much experience on mac's and dont repair them on regular basis. Need help guys.

PS: I'm using genuine magsafe245W cable for bench supply. Tried with genuine magsafe245W adapter as well.

[piernov]

Re: Macbook A1466 Dead

Resistance to ground on other rails from 3V/5V regulator?

[mon2]

Re: Macbook A1466 Dead

PP5V_S5 is powering the TRACKPAD. Suspecting an issue with the track pad.

Power down, remove the battery and then remove the trackpad cable.

Then power up again and see if this rail is stable.

[mcplslg123]

Re: Macbook A1466 Dead

I'm working on naked logic board and dc jack only. Nothing extra attached.

[mcplslg123]

Re: Macbook A1466 Dead

Resistance to ground on other rails from 3V/5V regulator?

Can you please specify which rails you are asking for??

[mcplslg123]

Re: Macbook A1466 Dead

No pin on TPS51980A is showing low resistance or shorted to gnd(other then GND Pin). Vreg3 is stable at 3.3V but Vreg5 is pulsing from 1.5-5.0V. Cap on Vreg5 replaced with same value, no result. Applied 5V on vreg5 pin from dc supply, consumption 0.055A-nothing heats up. Resistance on VREG5 -in diode mode-OL,Resistance mode-32K and still growing.PP5V_S4RS3 rails are all also pulsing. VIN is stable.

[piernov]

Re: Macbook A1466 Dead

Then go down the list of power rails to see which ones are pulsing and which ones are not, and check their resistance to ground.

[mcplslg123]

Re: Macbook A1466 Dead

Non-Pulsing Rails Resistance
PPBUS_G3H 56K
PPBUS_S5_HS_COMPUTING_ISNS 55K
PPDCIN_G3H_ISOL 56K
PP3V42_G3H 23K
PPVRTC_G3H 27.6K(SLIGHTLY PULSING FROM 3.30-3.42V)

Below mentioned rails are all pulsing:
PP5V_S5 -40K
PP5V_S4RS3-40K
PP5V_S0-40K
PP3V3_S5-8.6K
PP3V3_S4-26K
PP3V3_SUS-16K
PP3V3_S3-25K
PP3V3_S0-5.5K
PP1V05_S0-156Ohms
PP1V5_S0-0.15K
PP1V05_SUS-1.46K
PP1V2_S3-0.8K
PP1V8_S3-17.8K

Please advise and suggest further steps.

[mcplslg123]

Re: Macbook A1466 Dead

No advise??? Please.......

[mon2]

Re: Macbook A1466 Dead

Often the switching regulators will have a low resistance resistor to monitor the current drawn on that rail. These are current sense circuits. If the current sense network of parts is not valid, then the regulator will shutdown or toggle off then on in a 'chirp' mode.

For example, if the feedback leg after the current sense resistor is missing or damaged then the regulator believes that voltage went into the resistor but was zero or very low after the current sense part so this means we are applying a very high load or is shorted to ground. This condition, if real, will cause potential damage to the regulator so the pulsing on and off of the rail initiates.

This is to prevent damage downstream.

Please review each such regulator and inspect the current sense parts. Be sure that the resistor values are close to those listed in their schematics.

Also inspect the resistance to ground for each coil that will be present on the switching regulators.

[mcplslg123]

Re: Macbook A1466 Dead

Thanks@mon2 for responding. Resistance on all coils is already checked. Will check as per ur advise and give feedback on monday.

[mon2]

Re: Macbook A1466 Dead

More suggestions:

1) What is the exact voltage reading @ L7095, pin 2? This PP3V42_G3H must be @ 3.42 volts or very close to this value. At 3v3, it is too low and means something downstream is causing an excessive load.

2) If the above is not stable, also list the Vin to U7090 by monitoring D7005, pin 3. This is relatively easy SOT-23 / SOT-323 diode to probe.

3) PP5V_S5 is the output of an internal LDO regulator inside U7501. U7501 creates this LDO output with the assistance of PPBUS_S5_HS_OTHER_ISNS as the input @ pin U7501, pin 23. Tracing back PPBUS_S5_HS_OTHER_ISNS, see U5430, pin 5 and pin 4.

Confirm the voltage on pin 4 of U5430 = PPBUS_G3H with no pulsing. Ok?

Confirm the voltage on pin 5 of U5430 = should match PPBUS_G3H with no pulsing. Ok ?

If not ok, confirm these related resistors and current sense IC @ U5430.

Next, confirm the ENABLE pin of U7501, is it pulsing with the observed 5v0 voltage rail ? If not, then U7501 needs to be inspected further as it is deciding to pulse the PP5V_S4RS3 rail.

Observe the pulsing is present @ L7520, pin 1.

Next confirm the current sense parts for this rail @ U7401, pin 7 & 8 (R7556, R7547, C7518). They must all be present and of the correct values.

Confirm the voltage divider (feedback resistors) @ R7520 & R7521 are present and ok.

Confirm pin 22 of U7501 if P5VP3V3_VREG3 = 3v3 ?

U7501 is relatively easy part to source and may need replacement.

4) U1900 generates PPVRTC_G3H. U1900 is powered from PP3V42_G3H which again should be stable @ 3v42 or very close to this value. The PP3V42_G3H is intended to source 300mA so if this rail is lower, then someone downstream is guilty of too much loading.

On a similar logic board repair, the issue was related to the USB hub controller IC. After the USB controller (Microchip) was replaced, the logic board was repaired.

Perhaps consider to source a fresh U1900 and see if the rail still pulses.

[mcplslg123]

Re: Macbook A1466 Dead

@mon2, here is the feedback.
01. Exact voltage on pin2 of L7095 is oscillating between 3.38-3.44. Same on pin1.
02.Vin on D7005 is ok and stable at 15.6V
03.U5430 is not populated.
04.U7501 enable is pulsing
05.L7520, pin1 is pulsing but very slightly.
06. P5VP3V3_VREG3 = 3v3 -yes
07. PP3V42_G3H- oscillating between 3.38-3.44V

UPDATE:If i remove R5450, PPBUS_G3H becomes stable at 8.6V(pin2) and magsafe light turns from green to orange. 3.3V/5V is generated on coil, so U7501 is working.

Any further ideas as i want to learn from this issue??

[mon2]

Re: Macbook A1466 Dead

U5450 is missing ?? It should not be. Please confirm.

This is a simple part to source. Please apply it and test again.

Are any other parts missing? Was this a donor board by another tech or repair shop?

[mcplslg123]

Re: Macbook A1466 Dead

Nowhere I mentioned u5450 missing. May be some confusion in understanding. U5430 is not populated and U5450 is there.

Mb is fresh and was never repaired before. It even chimed once after re-soldering U1900 as it was corroded. Next morning it started pulsing. I believe U1900 is bad but I can't source the part for 2 reasons
01. Ali express is banned by govt of India due to border dispute with china.
02. Next option is to buy from New Delhi(capital city) but that too is under lockdown due to bad covid situation in my country.

[mon2]

Re: Macbook A1466 Dead

My error and apologies.

You can try VPN to bypass censorship. Have many relatives impacted in India. Lost my father a few weeks ago due to reaction with Pfizer. Do not believe the hype of vaccine safety. My father was strong as an ox and exercised daily. Had strong stomach pains and expired 10 minutes later. Still in shock. Pfizer Canada stated they will investigate but do not believe them. World is in chaos. We build for many medical companies and airlines. I know the responsibility that rests on our shoulders. Only wish they had done the same.

Let me check on if they are other options for you for sourcing this part.

Stay safe.

Kumar

[mcplslg123]

Re: Macbook A1466 Dead

VPN doesnt help as the ali payment system is censored and blocked. The site opens fine even without VPN but one cant make payment.

Sorry to learn about the sad demise of your father. May god give you the strength to beat this invaluable loss to you and your family. Infact we all are staring at that kind of scenario with covid menace. Hope everyone take precaution and stays safe.

[mon2]

Re: Macbook A1466 Dead

Thank you for your kind words.

Did some quick checks with Aliexpress vendors and as you said, they are not shipping to India. Always hated politics. The world needs to unite more than ever.

I would imagine that nearby countries are able to offer the same goods via a freight forwarding service to you?

If it helps, we can help to buy the goods and then ship to you from here in Canada. I know that the Aliexpress portal offers about 15-30 days to us which is the level of service we select for our repairs. Respectively, once it is here, we can ship to you by discounted DHL rates to your location.

Do you know if DHL is shipping parcels in India these days? Send us a PM and we can investigate the rates of say DHL small box with our company program. DHL claims that we have the best rate next to Walmart in the city for exporting worldwide.

PS: Miss the food from Halidram and the fresh jalebi


Can you post the voltage on L7560?

Value of SMC_BC_ACOK ?

Voltage on R5127 pin 1 ? Pin 2?

PPVRTC_G3H 27.6K(SLIGHTLY PULSING FROM 3.30-3.42V)
This rail should be @ 3v3 so the pulsing maybe an issue.

test the resistance of R1450, should be 330K