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820-3115-B No Light slow buzz...

E

Extreme

New member
Hello guys, this is my first topic here and I need some help, I am not an advanced technician but I try all my best to learn everyday ...
So I have an Macbook A1278, board code 820-3115-B, and I have no light on charger and I can hear a slight buzzing noise coming from the board.
I have 17V on F6905 .
But I don`t know where is coming from the slow buzzing noise, I can hear it only if I close the board to the ear.
What should I check for the first steps?

This is a very nice forum and I hope I will get the help here.

Thanks
 
2informaticos

2informaticos

Administrator
Staff member
Now post resistance to ground (diode mode) on same points.

Next, post voltages for ISL6259; pins 1, 2, 3, 9, 12, 13, 14, 15, 19, 20.
 
E

Extreme

New member
L6995 shows continuity both, on L7030 OL

For ISL6259 shows:

pin 1 0.01v
pin 2 16.85v
pin 3 4.01v
pin 9 0.02v
pin 12 0.00v
pin 13 0.00v
pin 14 0.00v
pin 15 0.00v
pin 19 5.08v
pin 20 5.06v
 
2informaticos

2informaticos

Administrator
Staff member
"L6995 shows continuity both"
Do you mean short (000) to ground?
Post exact value, on diode mode (red probe to ground) and 200 ohm scale too.

"on L7030 OL"
Maybe with black probe to ground; and viceversa?

"pin 12 0.00v"
This confirm missing 3V42; a short there is a good reason.
If yes, lift L6995 and see where the short remains.
 
E

Extreme

New member
Hello, glad that the forum is back.
Yes on L6995 is showing short to ground on both, at 200 ohm shows 02.0 on both
On L7030 with the black probe on ground in diode mode shows OL on red probe on ground shows short to ground on both sides
 
2informaticos

2informaticos

Administrator
Staff member
Did you really measure continuity without any power?
I hope you've removed both charger and battery...
 
2informaticos

2informaticos

Administrator
Staff member
"On L7030 with the black probe on ground in diode mode shows OL on red probe on ground shows short to ground on both sides"
Then how do you get these values?
You cannot get open line and short at same time, in the same point; no matter if probes are inverted.
 
2informaticos

2informaticos

Administrator
Staff member
How could you get different values in both sides of a coil?
Is just a coil, don't make measurements without logic.
.450 is a correct value.
You should get aprox 12v on L7030 now.
Check resistance between pins 17/18 and 27/28; not to ground...

"lift L6995 and see where the short remains."
Now your big problem is to find that short.
Try to inject tension with bench power supply.
Start with 1V and go up, no more than 4V, maintaining current bellow ampers limit...
 
E

Extreme

New member
As I said I am an beginner and I try all my best learn every day.
Will you be able to explain me better how to inject tension to the motherboard?
I have an dc power supply but I need some more guidance.

I hope you understand and I really appreciate your good wok here.
 
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