820-02536 board Air 2022 A2681 with power cycling on USB

[sekidata]

This 820-02536 presented with areas of liquid damage in the R_SPKRAMP area near UN000. I removed two corroded caps that had shorted PPBUS_AON and PP1V25_AWAKE_NAND to ground.

Now, connecting a charger gets PPBUS of 12.3V and 5.1 on USB-C. The charger gets to 20V but as soon as it does, the connection is reset to 5.1V and power cycles as such. Same behavior on all 3 ports.

I checked all large coils as well as the smaller MPMU and SPMU output coils and could not find shorts to ground. No component is getting hot during cycling. There’s obviously a short somewhere, how do I find it?

 

[2informaticos]

PPBUS_AON steady 12.3V?
What about 3V8_AON?

Also check MPMU and SPMU LDOs.

 

[sekidata]

PPBUS and 3V8 are steady for a few seconds, until the power resets and all rails dip to zero. Need to check the LDOs.

 

[sekidata]

All LDOs for both PMUs are there, some briefly, some steady.

 

[2informaticos]

Did you test with battery connected?

 

[sekidata]

I did and nothing changed at all. The battery could be empty though. I need to verify on another A2681 machine.

 

[sekidata]

Unfortunately I don't have a charged battery or a functional A2681. Anything else you would check?

 

[2informaticos]

Check diode mode on any switch, like in pages 48, 76, 78.

A good battery tester is a "must have" tool nowadays.

Battery Tool

Chipmunk Battery Tool

www.cmizapper.com

This is the cheapest and best option, especially designed for Apple repair.

Harald has also a battery simulator for some MacBook boards.

Battery Simulator

Battery Port Tester

www.cmizapper.com

 

[sekidata]

I just found out that PPVBAT_AON_CONN is 15Ω to ground. When I inject 3V into PPVBAT_AON_CONN, the only thing getting warm is the CPU. Does that make any sense?

 

[2informaticos]

Really strange.
Check resistance (ohm scale) between PPVBAT_AON_CONN and SMBUS_BAT_1V8_SCL/SDA lines.

Remove F5200 before injecting voltage.
If not, the voltage goes to PPBUS_AON through Q5265 (internal diode) and R5260.

 

[sekidata]

The battery connector was internally shorted. Removal of the connector removed the short. Now onto getting a new connector and back to testing with a good battery.

 

[sekidata]

With a battery connected, PPBUS stays at 11.6V. When I plug in a charger, PPBUS cycles between 11.6 and 12.3V.

 

[2informaticos]

Check diode mode to ground on UD200's pins.
It was probably damaged...

 

[sekidata]

All pins on UD200 measure good - identical to a known good board.

On battery power alone, the AON rails (PPBUS, PP3V8, PP1V8, PP3V3) are steady but all other power rails cycle (turn off every second).

 

[sekidata]

If I can't find any shorts on any secondary power rails, why are the PMUs cycling on and off? How do I find out why the charger resets?

 

[2informaticos]

What is the behavior of PPBUS_AON and 3V8_AON with charger alone?

 

[sekidata]

It’s still the same cycling as I wrote earlier. Both are steady for a few seconds (12.3 and 3.8) until the charger resets and all rails dip to zero.