820-00165 Backlight

[Bouba148]

Hi
I had this board as completly dead because of water damage, so I've fixed everything to the point i wanted to test that board in the chassis:
I had no backlight, so I checked the fuse which was dead then I replaced it ( what a BIG MISTAKE )
When I turned the board ON again, fume came out of the board and the blew again.
It completly melted the plastic of the LCD connector with the one of the lcd cable, so I'll have to replace the LCD cable.

But my concern is more to fix the backlight first:

The resistance of PPHV_S0SW_LCDBKLT to GND is 14.2 Ohms VS 4.8 KOhms for known good board
In diode mode with red probe to gnd I have for the same rail: 0.012v VS 0.570V for a know good board

So I suspected U7701 and L7701 and I removed i them but I had the same reading.

Now I would like to remove C7796 C7797 and C7799 maybe one of them is "leaking to ground".
What do you think? or you would advise me something else?

 

[Bouba148]

So I took out C8317, C779, C7797 and C7799 and still the same .
Maybe the connector itself?

 

[2informaticos]

"It completly melted the plastic of the LCD connector with the one of the lcd cable"
Didn't remove LCD connector yet?

 

[Bouba148]

It was just melted in front of pin 3 and 4 not all the connector sorry

Removed the connector:

Now it look likes to be OK, in diode mode I have 0.585V and the resistance to GND 4.8KOhms

 

[2informaticos]

Solder new connector.
When you connect LCD assembly again, check first if no short appears...

 

[Bouba148]

New connector soldered: OK
unfortunatly I had a short to GND on the backlight rail when I've connected the LCD cable.

So I've put another full LCD assembly, no short to GND, in diode mode 0.585V
When I turned the MBA ON: Display + Backlight OK

Now I'll have to order a new flex lcd cable to replace it....... I've never did it but I saw some videos on Youtube.......I hate doing that kind of task

Again Thans for your support.

 

[JohnB8812]

Good job, and you ALWAYS want to start with the LCD connector if you have a short on backlight. I usually will diode mode backlight output with and without the screen attached in a situation like that.

 

[Bouba148]

Thanks guys for your support,
A last question regarding that damaged flex connector:
With your experience do you think that maybe something else in that LCD assembly could be damaged?

 

[2informaticos]

Apart of video cable and LCD display?
Nothing else is connected through J8300 (display port connector).

When you connect new assembly, check first resistance to ground on J8300 pins; I talk about power rails, and eventually data lines.
Do not power on the board untill assure no short/low resistance on any of these pins...

 

[Bouba148]

Already connected new assembly yesterday thanks, as you advised me yesterday also , i've checked everything before turning ON the MBA with the new assembly.
Now I just hope the old assembly has just the flex cable to be replaced and not something else blown inside.

 

[2informaticos]

If you plan to change the cable, do the same test when you connect old assembly.
A bad reading will directly point to LCD display then...

 

[Bouba148]

2Informaticos,

I will let you know

Thanks so far