pp3v42 not coming on.

[patrickribbsaeter]

Green light is missing.
R6905 pin 1 = 19v, Pin 2: 0.027mv

What is pulling it down?

I have changed the D6905 and same problem.

could it be the chip U6990 that is pulling it down? ive changed that one as well.

I removed all the caps connected to ground under U6990.

any ideas pls why R6905 gets 19v on side pin1 but nothing on pin2..??? I have changed to new resistor 3 times already. Weird!

 

[2informaticos]

Why don't you post 820-xxxx code?
In your picture, only 6x 4.7uF caps and U6990 are connected after D6905.
Check diode mode to ground on that point, before apply power.
Also check if D6905 is not shorted too.
Did you replace R6905 with correct value?

 

[patrickribbsaeter]

sorry, ive been off the forum a while so forgot to post the board nr.

820-3208 Macbook Air

R6905 is original and has the same value (10).. Ive changed the diode as well. In case its pulling it down. Still doesnt work. very strange! Could it be somehthigng inside ethe board thats messing it up?

never seen before a Resistor having volateg on one pin and nothing on the other even with a new resistor.

 

[2informaticos]

"Check diode mode to ground on that point"
I was expecting you will post it here.
10 ohms resistor should have voltage on both sides; unless is blown.

 

[patrickribbsaeter]

R6905 both pin showing "OL" open line in diode mode.

I injected voltage and tried to hunt for short. No short from what I could see.

The 10 ohm resistor is new.. Its very weird..

 

[patrickribbsaeter]

There is a short on this capacitor pad C6991. Even though i took away the capacitor. its still shorted to ground. How is that possible? must be a short under/inside the board itself. The cap was burnt before I took it off. That cap is attached to U6990. Could it be U6990 isbeing pulled down and thats why the Diode also cant pull the voltage?

 

[2informaticos]

There are 6x 4.7uF and U6990 connected.
Cannot be so dificil to find the culprit; even removing one by one...

 

[patrickribbsaeter]

That's a strange thing.. There must be an internal short on the board.. I have removed all the caps. all of them 6x 4.7uF. One of the shorts the one I posted C6991, that pad is shorted to ground.which is the line for PPVIN_G3H_P3v42G3H. So how do I go about to fix that if it's an internal short on the motherboard? is it possible. or should I just tell the customer this board is not fixable. It seems so

I will try to remove the IC U6990 again and see if the short is gone and revert back to you asap.

 

[2informaticos]

First remove U6990.
If still short, look if any pad is damaged.
Then scratch the board, try to isolate that pad.
You may need to cut off the trace in 2 points and make a bypass.

 

[patrickribbsaeter]

1. i detached U6990, i have not short/continuity to ground.
2. I placed another U6990 from donor board.
3. I changed the resistor 10ohm resistor before diode D7005. And the 10ohm resistor(R7005) broke right away. What could be the cause for that?

 

[2informaticos]

Do you still have short on PPVIN_G3H_P3v42G3H when U6990 is removed?