A1990 820-01041-A no power

[hgoncalves]

Hi.

I have an A1990 820-01041-A with no power. Only 5V on ampmeter, and 0A.

Client said that it had the mac storaged for a long time, and now it just don't power on.

No signs of any damages on the board.

Diode readings on the big coils seams to be ok (not sure cause don't have any good board to compare).

PPBUS_G3H seams to be shorted. 0.020 on diode reading and 0.165V

Can I inject voltage here to see if anything gets hot?

 

[2informaticos]

Check if any coil has similar reading.
Don't forget SSD coils!

You can also remove F7000/1 and check where the low value remains.

 

[hgoncalves]

I forgot the SSD coils...

L9080/1 seams low. 0.002 on diode reading

 

[2informaticos]

Shorted NANDs?

 

[hgoncalves]

Can I inject 1V there to see if gets hot?

 

[2informaticos]

Remove first U9080 and check if still short.

 

[hgoncalves]

After removing U9080, the diode reading increased to 0.006.

I'm not sure if this reading is ok, because I don't have other board to compare it, but now I have 20V on ampmeter, and 0.15A (them reboots)

Shoul I replace U9080?

 

[2informaticos]

Not enough to replace u9080.
It is bad and should be replaced, of course.

But you have at least one NAND burnt.
You may need to replace all NAND chips.
This repair is expensive; confirm first if client wants to go ahead.

 

[hgoncalves]

OK. TKS. Do you have any trusted supplier for this NANDs?

 

[hgoncalves]

Hi,

It seams that it had 3 burnt NANDs.

The client said that the Mac had 500GB of storage, and so I've ordered 500GB NANDs for this model.

The problem is that the Mac had 4 nands originally, and now I only have 2 NANDs.

I've replace the 4 original NANDs for the 2 new nands, but now it fails on the DFU restore.

Mac has 19.8V, but it's oscillating between 0.02A, 0.25A and 0.73A.

Can I replace the 4 nands for just 2?

 

[2informaticos]

Did you properly initialize the NANDs with JC P13 programmer?

 

[hgoncalves]

No, I didn't.
How can I do that? Can you indicate a procedure for this?

 

[2informaticos]

 

[hgoncalves]

TKS. Just one question please:

JC P13 says the Mac had 4 NAND (1 x 128GB + 3 x 64GB). How can I use just 2 NANDs of 256GB with P13?

 

[2informaticos]

Check S4E Parts on page 3...

 

[hgoncalves]

Hi.

I'm sorry. I can't understand how to do it. For what I see in the manual, I think that I can't use just 2 x 256 GB NAND. Is that correct?

If not, can you please explain how to do it?

Sorry...

 

[2informaticos]

The video is for exact your MLB model...

 

[hgoncalves]

TKS. NAND upgrade solved the problem.