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Old 09-24-2012, 09:05 PM   #1
inflex
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Default Dell 1545 LCD backlight dead after replacement

Replaced a nicely shattered Dell 1545 laptop LCD only to be greeted with the normal boot screen but alas, no backlight, no matter what I did.

I've heard that there's a couple of fuses feeding the LED backlight and was wondering if anyone could point out specifically where F8 is, because it would -seem- that F1 is fine after trying to short with a low-ohm-resistor.

Paul.
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Old 09-24-2012, 09:43 PM   #2
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Default Re: Dell 1545 LCD backlight dead after replacement

I've pulled the mainboard out, F1 is certainly seeming okay, passes continuity test on the meter no issues. Can't find F8 for the life of me though.
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Old 09-25-2012, 01:54 AM   #3
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Default Re: Dell 1545 LCD backlight dead after replacement

Might, or might not be related, but here's some corrosion I found on the board on the other side of where the ATi chip is.

I'm thinking this might well just about render the system a bin-job and mean I've wasted $90 on the LCD

*EDIT* Any chance someone could take a photo of their 1545 board in this same location (see the 3rd picture) so I can evaluate if there's parts missing and what the copper layer should look like.

It's just near the Intel bridge chipset.

Looking at the "corrosion" spread, it looks a bit like an oval which makes me think the ceramic cap near the R5124 text might have had a hot jet failure. However, until someone can bring me a schem or a photo of the same area on a good board, I can't tell
Attached Images
File Type: jpg corrode-1.jpg (336.6 KB, 56 views)
File Type: jpg corrode-2.jpg (239.6 KB, 47 views)
File Type: jpg picDSCF0058.JPG (219.6 KB, 50 views)

Last edited by inflex; 09-25-2012 at 03:00 AM..
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Old 09-25-2012, 07:10 AM   #4
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Default Re: Dell 1545 LCD backlight dead after replacement

*UPDATE*

Managed to get the schem for the board and have found that the parts on the corroded area happen to coincide with the PANEL_BKEN, specifically R5213 which looks to be nothing more than a jumper link / R0. The trouble I have now is determining -where- the R0 should go.

Schem is at http://dxp.me/i/1545.pdf

R5213 is listed on Page 52, and links back to page 29.

Will keep you all up to date - would be good if I could get a photo of someone else's board

*UPDATE #2* Can someone help me find R157 ? It's a 10K pulldown resistor on pin 9 of the Winbond chip, which links to the ATi PANEL_BKEN, I want to find it so I can then track back to the ATi chip as to which pad I need to link again.

Last edited by inflex; 09-25-2012 at 07:44 AM..
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Old 09-25-2012, 08:17 AM   #5
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Default Re: Dell 1545 LCD backlight dead after replacement

Here's the board cleaned up a bit more, I'm strongly suspecting I'm going to need to link the two traces that led to the R5213 that now doesn't exist. Of course, it still does bother me that I don't know precisely -why- that part is missing in the first place, additionally I worry that some serious damage was done to either the ATi chip or the Winbond chip, but I guess I won't find out until I reconnect these two pads.

The trick for me right now is how in the hell to safely etch back the solder mask without destroying the copper. I could use something like a 0.5mm bit and try scrape away the mask at the vias that I want to connect, but that's a case of "if you bite too far, it's ALL over".
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Old 09-25-2012, 08:30 AM   #6
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Default Re: Dell 1545 LCD backlight dead after replacement

It may also be possible to wire the backlight control signal to a signal that's only active when the laptop is operating normally - for example, the power LED. You stand little chance of repairing that damage, although it doesn't look like there was a component there in the first place.
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Old 09-25-2012, 08:48 AM   #7
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Default Re: Dell 1545 LCD backlight dead after replacement

If I can find R157 on this board, it'd help a lot, certainly a lot easier to work from that component than trying to attach some #32 to a single pin on the Winbond chip.
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Old 09-25-2012, 10:12 PM   #8
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Default Re: Dell 1545 LCD backlight dead after replacement

Fixed!!!!

What a wonderful sight to see the backlight come good.
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File Type: jpg picDSCF0091.JPG (106.2 KB, 56 views)
File Type: jpg 1545-fixed.jpg (128.5 KB, 56 views)
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Old 09-26-2012, 05:31 PM   #9
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Default Re: Dell 1545 LCD backlight dead after replacement

Been running now for the last 12 hours all 100%. Fixed up other issues with the laptop (bent DVD faceplate eject pin, broken front bezel hinge cover, both with bicarb+superglue, great stuff!).

Having the schems was the key to it all, without those I'd have had no real reliable chance of working out what was going on. I still wonder though if the corrosion was due to the screen breaking causing the jumper to fry (very odd, would have expected a lot of other damage elsewhere), or if it was just a very coincidental drop of *something* landing on the right position to cause the panel backlight control line part to melt away (again, very odd, more so because there's no visible indication on any of the chassis panels in that there was any sort of liquid).

*EDIT* Added photo of fix with the liquid-tape over it, all safe now.
Attached Images
File Type: jpg picDSCF0098.JPG (85.3 KB, 30 views)
File Type: jpg picDSCF0097.JPG (223.0 KB, 44 views)

Last edited by inflex; 09-26-2012 at 05:56 PM..
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Old 09-26-2012, 05:34 PM   #10
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Default Re: Dell 1545 LCD backlight dead after replacement

Nice fix.

It's a little weird to see the disembodied motherboard and LCD working! But great when all assembled. Another one fixed!

You knew for sure it was a 0 ohm from schematics?
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Old 09-26-2012, 05:55 PM   #11
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Default Re: Dell 1545 LCD backlight dead after replacement

Tom66, according to the schem it's just a link / 0R (R5213) .

Was very happy to see it fire up. Though as mentioned, it's still a big mystery as to 'how'.
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Old 12-15-2012, 04:29 PM   #12
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Default Re: Dell 1545 LCD backlight dead after replacement

ty all members for sharing your problems herei had backlight problems after replacing broken lcd screen. F1 fuse was the problem for me. THX ALL
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Old 12-20-2021, 05:07 AM   #13
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Default Re: Dell 1545 LCD backlight dead after replacement

Nice job mate...
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