A1398 820-00138-A no power

[hgoncalves]

Hi,

I have an A1398 820-00138-Awith no power. It has green light, no fan spin, and puls 0.027A from bench PSU.

I have no history, but It seams that someone already replaced C7376.

PPBUS_G3H is shorted (0.002 diode reading, and 0.1 ohm), and I have the same reading on L7130. All other big coils seams to have normal diode readings.

Can you help?

 

[2informaticos]

Remove F7140 and check which side the short remains.
If all other big coils show good resistance to ground, then is safe to inject voltage.
As you have almost pure short (0.1 ohm), start with 1V; should be more thyan enough.
Use powerfull cables and set amp limit to max first (on PSU).

 

[hgoncalves]

Hi,

It seams that both lines are shorted.

With F7140 removed, I get these values:

PPBUS_G3H and PPVBAT_G3H_CHGR_REG = 0.002 on diode reading and 0.2 ohm to ground on both

 

[2informaticos]

This is 15" machine, has 2 (TWO) fuses; so remove both F7140/41.
I can't believe than need an explanation for this...

 

[hgoncalves]

I thought it was necessary, but I also thought maybe there was a reason for it....

After removed both fuses, I've injected 2V and reached 5A but I can't see anything geting hot (strange but I can't see it).

However, I notice that C7325 was missing, and the pad had exploded (PPVIN_S5_HS_COMPUTING_ISNS) It's not there, and was covered by UV glue.

 

[2informaticos]

You may have short inside the board, between its copper layers.
If you are using 5A lab PSU, it may not inject anything; if gets in protection mode.
Start with 1V and increase voltage until get 4-4.5A.

 

[hgoncalves]

Hi,

I've started with 1V and finished with 2.30V and 4.6A of consume on PSU, but can't find anything geting hot...

Should I scrap a little bit on the burnt pad of C7325?

 

[2informaticos]

Are you using powerfull cables?
The idea is to heat the bad component, not the cables.
IR camera available?

 

[hgoncalves]

I'm using the same cables that I usually use, and with a IR cam.

 

[2informaticos]

With aprox 9W you should be able to detect an hot spot.
Check with voltmeter if you realy get 2.3V on the board, when PSU shows 4.6A...