A2289 820-01987 no power

[hgoncalves]

Hi,

I have an A2289 820-01987 wit no power. I't only puls 5V from Ampmeter.

PPBUS_G3H seams to be shorted:

PPBUS_G3H = 0.006 on diode reading, and 2.8 ohm to ground

PPBUS_HS_CPU has the same readings.

Can you help?

 

[2informaticos]

Check if any coil gives the same reading to ground.

 

[hgoncalves]

Hi,

Today, I have on PPBUS_G3H, 3.5 ohm to ground, and I get 3.2 ohm to ground on L7410/20.

 

[2informaticos]

Check resistance (ohm scale) between L7410/20 and PPBUS_G3H.

 

[hgoncalves]

Hi.

Resistance between L7410 and L7420 = 0.3 ohm

Resistance between L7410/20 and PPBUS_G3H = 6.9 ohm

 

[2informaticos]

Then the short doesn't come from U7410/20.
If no short between any coil and PPBUS_G3H, then is safe to inject voltage.

 

[hgoncalves]

Hi.

The only thing that gets hot seams to be the CPU. Is it posssible to replace it by one from a different donor board?

Is there any way to be sure that the culprit is the CPU?

 

[2informaticos]

CPU gets hot injecting voltage into PPBUS_G3H???

 

[hgoncalves]

Hi,

Yes, It seams so. I didn't see any trace directly to the CPU, but it seams to be the one who's geting hot.

I've removed F7000 and injected voltage there (PPBUS_G3H).

With 2.5V, it reaches 0.9A, and on the thermal cam nothing gets hot, except CPU. I've supposed that it was on the other side of the board, but it realy seams that it is the CPU.

Dosen't make sense?

 

[2informaticos]

Then you should have problems with one of the chips from CPU power supply.
Remove (one by one) U7210/20/70 and U7410/20.

 

[hgoncalves]

Hi.

After replacing U7210 the PPBUS_G3H short is gone.

However, on boot, when the apple logo appears, the mac shutsdown.

Any idea?

 

[2informaticos]

Same in safe mode?
You can try DFU revive; restore, if no data needed.

 

[hgoncalves]

Hi.

DFU revive solved the problem.

TKS!