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[SOLVED]820-3115 - Led Driver keep blowing - liquid damaged. - Board-B

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Alan.L

Alan.L

Member
Led Driver keep blowing without a screen connected.

i had to replace U9701 like 5 times because I needed to know where the pop noise and smoke coming from.

LVDS connector has been replaced.

R5400 was corroded,

thunderbolt has been removed because it was making a clicking noise.


i get an image on the screen but no backlight.


PPBUS_G3H = 12.58v
PP5V_S0 = 5.077v
PP3V3_S0 = 3.3v


where should i start looking, diode mode on lvds?
 
Alan.L

Alan.L

Member
i haven't touched the fuse. its intact in original form.

reckon i should remove the LVDS connector and see if still blow?
 
smiba

smiba

New member
Check resistance between PPVOUT_SW_LCDBKLT and PPBUS_SW_LCDBKLT_PWR_SW to ground

Also make sure the chip is aligned properly as I had a backlight chip blow up before. Both of these power lines are straight next to a ball carrying a path to ground
 
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Alan.L

Alan.L

Member
smiba said:
Check resistance between PPVOUT_SW_LCDBKLT and PPBUS_SW_LCDBKLT_PWR_SW to ground

Also make sure the chip is aligned properly as I had a backlight chip blow up before. Both of these power lines are straight next to a ball carrying a path to ground
Click to expand...

i did like over 5 times , . this driver is piss easy to do.

resistance between PPVOUT_SW_LCDBKLT and PPBUS_SW_LCDBKLT_PWR_SW to ground is OL with broken driver.


[B said:
dukefawks[/B];n25138]The driver will not blow due to a short on the backlight rail. Orientation correct?
Click to expand...


yes,


nxaDupS.jpg


HFFYDPL.jpg




with suspect broken led driver, these are the measurements:

with a screen connected on LVDS:

Pin2 = 3.26v
pin3 = 3.26v
pin4. = 3.3v
pin21,22 = 12.57v

pin1

fuse = 12.58v

PPVOUT_SW_LCDBKLT = 12.58
PPBUS_SW_LCDBKLT_PWR_SW = 12.59v
 
Alan.L

Alan.L

Member
i've removed the fuse.

Pin1 - PPBUS_G3H = 12.59v
Pin2 - PPBUS_S0_LCDBKLT_FUSED = 12.43v

whats going on here.


i've replaced Q9706 - no change.
 
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Alan.L

Alan.L

Member
anyway to hack this?

i've disabled Q9706's Pin1 - this pin is generating 12.43v

now PPBUS_S0_LCDBKLT_FUSED is getting = 2,8v. (where this voltage come from? )




---------- --------------------------------------------------------------------------------------------------------------

with fused & Q9706 removed

PPBUS_S0_LCDBKLT_FUSED is 0.200v

PPBUS_SW_LCDBKLT_PWR_SW = 12.58v. (should be 0v right)
 
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D

dukefawks

Administrator
Fixing just the leak in the backlight output is not going to help. The LP8550 keeps dying cause the 12V is also getting to more places. Pull the 8550 and measure all the pins for 12V.
 
Alan.L

Alan.L

Member
with fused soldered and LP8550 removed.

PPBUS_G3H = 12.58v

LP8550:

1. = 0v
2. = 0v
3. = 3.111v
4. = 0v
5. = 12.57v
6. = 12.58v
7. = 12.58v
8. = 0v
9. = 0v
10. = 0v
11. = 5.077v
12. = 0v
13. = 0v
14. = 3.3v
15. = 0v
16. = 5.077v
17. = 0v
18. = 3.32v
19. = 3.332v
20. = 0v
21. = 0v
22. = 0v
23. = 0v
24. = 0v
25. = 0v
 
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Alan.L

Alan.L

Member
Not 100% sure, smoke comimg from somewhere everytime i put a new LP8550, i've ran out LP8550. I,ve show you in a video.
 
Alan.L

Alan.L

Member
no, only time it will smoke if i put a new LP8550. already wasted 10 LP8550 :( . i'll have to wait for a week from china.
 
Alan.L

Alan.L

Member
pack of LP8550 arrived this morning. I've then replaced the LP8550 for three more times, but the last one didn't smoke, so i guess whatever was shorted it burnt out over time. :rolleyes:

now the board is working and ready to rock once again :cool:
 
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Alan.L

Alan.L

Member
nothing to do with the bad batch, I've used the same spool to fix many air boards and seems to be fine. i blame the board :p

I've tested the laptop for 18hours with on and off. the backlight seems to be stable, so I guess this thread can be close.
 
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