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Got a laptop screen bought brand new and now the backlight…

Customer Question
Got a laptop screen bought...
Got a laptop screen bought brand new and now the backlight doesn't work. Replaced the surface mount IC controller for back light and still no go. Blew a fuse for the back light chip but it seems to be grounded when the cables are all hooked up. I'm thinking why would they fuse link a ground connection ???
Submitted: 5 months ago.Category: Laptop
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Answered in 4 hours by:
3/17/2018
Laptop technician: Pete, Computer Expert replied 5 months ago
Pete
Pete, Computer Expert
Category: Laptop
Satisfied Customers: 20,645
Experience: CISCO certified computer and networking expert
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Hi, I'm Pete. Welcome to JustAnswer! I'm reviewing your question now, and will post back with your reply ASAP.

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Laptop technician: Pete, Computer Expert replied 5 months ago

Do you have a voltmeter to check if the backlight is getting power ok?

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Customer reply replied 5 months ago
YA I do but without a schematic or datasheet for the pinout of the back light controller hard to know which pin(s) are the power. The oddest thing is the fuse that blew when I tried to fix 3 broken connections on a ribbon cable extension which was required for the replacement. (Got torn by accident, have a new one again). The 3 connections that got torn were all tied together at the pcb so I just jumpered it and when it powered upit blew the fuse. My knowledge about electronics tells me that you don't normally fuse a GND connection. But when the cable is attached that connection at the fuse becomes grounded (chassis gnd) So I haven't been able to find the power for that section of the pcb. Making measurements with DVOM is very difficult at the IC since it is so tiny and is leadless so it's tough. If by some chance that fuse link has become shorted to ground, my thinking is that it should keep blowing the fuse again but it doesn't. I'm gonna keep trying to find a power supply for that IC. There are of course other IC's and I have replacements for them but after checking they seem totally isolated from the area where the fuse blew. ie. they have a different PS possibly ?
Laptop technician: Pete, Computer Expert replied 5 months ago

The IC that controls the power may have blown if there was a short.

Try to find the + and - power supply connections to the backlight (at the backlight itself) and work backwards from there.

If power is getting to the backlight but it isn't powering on, then the backlight itself is shot.

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Customer reply replied 5 months ago
Yeah I thought about the backlight possibly being damaged too. But the IC would/should have isolated it from a short. Again trying to get probes in to measure those pins on the back light ribbon connector will be very difficult but I will try. There are 4 test points I can get at that go to the BL connector but there are a few more pins that don't have test points, hopefully they are just GND's
Laptop technician: Pete, Computer Expert replied 5 months ago

Ok, let me know how it goes.

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Customer reply replied 5 months ago
Will do
Laptop technician: Pete, Computer Expert replied 5 months ago

No need to reply back until you need me as I am required to respond as promptly as possible :)

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