MacBook Pro Unibody - No Backlight - Logic Board Question

[Dadioh]

The boost diode is the device with 74 written on top. The end with the white stripe is where you measure the backlight voltage. The device you circled as FET is the NAND gates that provide the enable signal for the backlight circuit. If you pm me I can probably walk you through a few diagnostics to help isolate the issue.

Hi, first of all, thank you all (mainly Dadioh of course) for this great thread.

My problem is basically the same as most of you - non working backlight, everything else seems fine. I bought the macbook from ebay as AS-IS, though that I will replace the screen, however I found out, it was spilled on it... than found this thread and read all through it. But I never found exactly the same model as mine (13 Macbook Pro 2,66GHz, mid 2010), so here's the picture:

http://dl.dropbox.com/u/2635790/quIfTtoLygA1pOSJ.jpg

Can anyone confirm, that I marked the components right, please? (I'm pretty sure about all of them except the boost diode.)

I measured the fuse (or what I expect to be a fuse), but it seems ok (closed circuit, very low resistance), so that leads me to conclusion that the WLED driver is damaged. However I don't really know how to proceed from here, how to make sure it is damaged, because it's a bit different component that was talked about in this thread (mine is LP8545 versus LP8543 which is in the previous macbook models...).

Also I'm a bit worried about the WLED availability... I checked the newark.com, digikey.com and avnetexpress.avnet.com but non of them have the component in stock
Anyway, I read a lot of success stories, so I'm hoping for the best.

Any ideas?

LP8545 datasheet (my model)
LP8543 datasheet (previous models)

 

[mryallups]

This Thread should seriously be published.
I have one question that I don't think has been flat out answered yet and if it has I am sorry for re asking.

I have a macbook A1342 That will boot and can run on an external display, but will not display anything on its own display. I tried holding a flash light up to it to see if the is an image but I can's see anything. I replaced the screen and still have the same issue. Does this mean that my LVDS cable is bad?

I did located the fuse and I am thinking about replacing it, but feel a little nervous about it. I don't want to try to replace it and then not even fix the problem.

 

[alexfunari]

Hope this helps, wasn't sure what was considered a good pic of a bad one so I put them all up.

 

[peislander]

display wireless problems

Hey,I got a late 2008 A1278 motherboard that was working before I tested a screen I got off ebay.The screen was working fine but didn't have a wireless card installed.I ordered a wireless card from ebay & the problems start.
It would just display a white screen.Tried a different screen ...same thing.Took out logic board & noticed a bit of black on a resistor it measured 2k.Measured a good board & it was only 2 ohm. Replaced tiny 2 ohm resistor & the display works fine but the wireless is not working.Does anyone know where to look for the wireless chip or got a schematic.Thanks

 

[vyrcoop]

Thanks for the reply. Actually, I read through the thread again and found out about the boost diode and measured it (using this picture: https://forums.macrumors.com/attachment.php?attachmentid=275509&d=1299882010).
It read something about 9-10V as opposed to 27V, which it should, so I made a conclusion it's the damaged WLED driver. (I managed to order it from avnetexpress.avnet.com, now waiting untill it arrives to Europe).

But.. what about the NAND gates and enable signal? How do I measure that? I checked the resistors around.. and all of them seems to be alright.

I found the schematic of the backlight driver, hope that helps: http://cl.ly/1T1m2C0A2a3W2K3Y3t0j/o

(btw. can't PM you)

The boost diode is the device with 74 written on top. The end with the white stripe is where you measure the backlight voltage. The device you circled as FET is the NAND gates that provide the enable signal for the backlight circuit. If you pm me I can probably walk you through a few diagnostics to help isolate the issue.

 

[vyrcoop]

13 MBP mid 2010 2.66

Hi everyone, I found the glitch!

Actually, my brother did, but anyway, here's what happened.
We followed the schematics (http://cl.ly/1T1m2C0A2a3W2K3Y3t0j/o), we were checking the components around the WLED driver. The problem was in the resistor which is connected to pin 4 (enable pin). This resistor should be 300 kOhms. We measured it and it read 300k, so we thought it's ok. But than we turned on the macbook and measured the voltage on it - and here was the glitch - one pin of the resistor was 11.8V but the other pin was 0V. The measured resistance probably wasn't the resistance of the resistor, but the resistance "around" it. (That's why you're supposed to measure electrical component while it's not connected to the circuit )
Next, my brother tried to measure the resistance on the enable pin (4) - and - the backlight turned on! Basically, he brought the signal on the enable pin with the multimeter (when you measure the resistance, the multimeter puts some voltage on it's electrodes).
Anyway, the point is, the resistor was wrong, I'm going to buy one tomorrow and replace it.
The 4pcs of WLED driver (LP8545SQ) that I ordered from across the sea for $30 should arrive in a week or two. They are hard to find on our continent (Europe) but it seems like I wont need one and I also bought 3 spare pcs, so feel free to contact me, if you need one

Again thank you all for this thread, I would have probably never solved this without your help.

Here's the schematic: http://cl.ly/3J3B0E3x1G2H1H2p2y3d/o

 

[alexfunari]

Hope this helps, wasn't sure what was considered a good pic of a bad one so I put them all up.


[url=http://img708.imageshack.us/img708/1034/dsc02353n.th.jpg]Image[/URL]
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Can anybody help? Thanks guys!

 

[westbound]

1342 wd

Hi,
I bought a dead 1342 that was water damaged. I cleaned up the board thoroughly with alcohol and turned it on. It booted normally, but after a few minutes the backlight started to flicker violently. I turned it off and let it sit a couple of days. when i turned it back on the backlight flashed briefly then went out. it hasn't worked since(backlight). It works fine, but with no backlight.
Anybody know where abouts the fuse is located?

 

[Doogiechap]

my earlier comment about positive ground took a while to make sense. the "wires" are coaxial. the small center wire is not easy to bare and solder. (was grounding to shield)
fed external 24volt to one Red (21)cut from Ipex and one Blue (26)cut from Ipex.
Screen lights up functionally bright and shows that the rest of the computer is undamaged.(mouse, wireless, Keyboard all working)
proof this machine is worth the remaining salvage effort to assemble a simple voltage boost pump.

Hi tlars,
I'm the new proud owner of an eBay purchased MBP in a similar condition to yours (some spectacular repair/ removal attempts of the WLED driver) and was interested to see how you had faired with your voltage boost pump idea. I was thinking of adding a dil relay that could run of the keyboard illumination output to switch the backlight off in sleep mode.
and....
Dadio thanks for all of your support and efforts with this thread, your help is truly appreciated !

 

[peislander]

Can anybody help? Thanks guys!

Hello Alex
Your fuse is best seen in the 3rd from bottom pic.With the heat sync & fan's facing you,look up & to the right of the right fan & the fuse is beside a big gray inductor.It's brown with a white dot on it.Good luck & we hope that your fuse is blown,cause that's the easy fix.Later

 

[alexfunari]

Hello Alex
Your fuse is best seen in the 3rd from bottom pic.With the heat sync & fan's facing you,look up & to the right of the right fan & the fuse is beside a big gray inductor.It's brown with a white dot on it.Good luck & we hope that your fuse is blown,cause that's the easy fix.Later

Forgive me for being foolish, but is this the pic you're referring to?


[IMG=http://img199.imageshack.us/img199/4655/dsc02364mc.th.jpg][/IMG]

Any chance you can circle the fuse? Is it part F9800? I have the schematics for the logicboard and located that already.

 

[alexfunari]

Is this the part? Thanks! (trying to help out! LOL) 15'' A1286

 

[westbound]

This Thread should seriously be published.
I have one question that I don't think has been flat out answered yet and if it has I am sorry for re asking.

I have a macbook A1342 That will boot and can run on an external display, but will not display anything on its own display. I tried holding a flash light up to it to see if the is an image but I can's see anything. I replaced the screen and still have the same issue. Does this mean that my LVDS cable is bad?

I did located the fuse and I am thinking about replacing it, but feel a little nervous about it. I don't want to try to replace it and then not even fix the problem.

Hi, Can you tell me where the fuse is located. The only fuse I see with a white dot is located about an inch to the right of the Lvds cable.
Thanks,

 

[vyrcoop]

Thanks again, backlight is working!

 

[Dadioh]

Is this the part? Thanks! (trying to help out! LOL) 15'' A1286

That won't be it. The fuse is in an 0402 size package (the smallest ones you see). That part is an 0603 package. You are looking for a beige 0402 size with a white dot or an "F" on the top of it.

http://en.wikipedia.org/wiki/Surface-mount_technology#Package_sizes

 

[Dadioh]

Hi,
I bought a dead 1342 that was water damaged. I cleaned up the board thoroughly with alcohol and turned it on. It booted normally, but after a few minutes the backlight started to flicker violently. I turned it off and let it sit a couple of days. when i turned it back on the backlight flashed briefly then went out. it hasn't worked since(backlight). It works fine, but with no backlight.
Anybody know where abouts the fuse is located?

I haven't worked on that particular model before (polycarbonate unibody) but I would bet the schematic is almost identical to the aluminum unibodies. That being said you will be looking for a tiny 0402 package beige in colour and with a white dot or occasionally an "F" printed on top. It should be somewhere close to the LVDS connector but could be either front or back.

 

[Dadioh]

Hi everyone, I found the glitch!

Actually, my brother did, but anyway, here's what happened.
We followed the schematics (http://cl.ly/1T1m2C0A2a3W2K3Y3t0j/o), we were checking the components around the WLED driver. The problem was in the resistor which is connected to pin 4 (enable pin). This resistor should be 300 kOhms. We measured it and it read 300k, so we thought it's ok. But than we turned on the macbook and measured the voltage on it - and here was the glitch - one pin of the resistor was 11.8V but the other pin was 0V. The measured resistance probably wasn't the resistance of the resistor, but the resistance "around" it. (That's why you're supposed to measure electrical component while it's not connected to the circuit )
Next, my brother tried to measure the resistance on the enable pin (4) - and - the backlight turned on! Basically, he brought the signal on the enable pin with the multimeter (when you measure the resistance, the multimeter puts some voltage on it's electrodes).
Anyway, the point is, the resistor was wrong, I'm going to buy one tomorrow and replace it.
The 4pcs of WLED driver (LP8545SQ) that I ordered from across the sea for $30 should arrive in a week or two. They are hard to find on our continent (Europe) but it seems like I wont need one and I also bought 3 spare pcs, so feel free to contact me, if you need one

Again thank you all for this thread, I would have probably never solved this without your help.

Here's the schematic: http://cl.ly/3J3B0E3x1G2H1H2p2y3d/o

I actually did have one I fixed that had a bad resistor on the enable pin. Going from memory it was something like a 300K 100K voltage divider off the 12V rail giving a 3V signal on the enable pin. It caught me by surprise because resistors rarely fail in my experience. Still not sure what caused that one to blow. But good work diagnosing vyrcoop

 

[peislander]

Is this the part? Thanks! (trying to help out! LOL) 15'' A1286

Image

It's at the other end of your arrow & down a bit.Good luck Yes it is f9800

 

[westbound]

Fuse

I haven't worked on that particular model before (polycarbonate unibody) but I would bet the schematic is almost identical to the aluminum unibodies. That being said you will be looking for a tiny 0402 package beige in colour and with a white dot or occasionally an "F" printed on top. It should be somewhere close to the LVDS connector but could be either front or back.

Hi Dadioh,
Could this be it? There isn't any solder to connect the probes.

 

[Dadioh]

Hi Dadioh,
Could this be it? There isn't any solder to connect the probes.

View attachment 296801

That could absolutely be it. Is that on front or back of the board? If you have access to it you could power on the board and then carefully measure the voltage on either side of the fuse. It should be 12V on both sides.

 

[westbound]

That could absolutely be it. Is that on front or back of the board? If you have access to it you could power on the board and then carefully measure the voltage on either side of the fuse. It should be 12V on both sides.

Its on the front close to the lvds. I'll check for voltage and report back.

 

[Dadioh]

Its on the front close to the lvds. I'll check for voltage and report back.

Ideally you check the voltage down at the solder pad of the circuit board and not on top of the component. The reason being, if the solder connection is good on the input of the fuse, the fuse is good, but the other end of the fuse is corroded and not contacting the circuit board solder pad you would measure 12V on the fuse end but that would not be making it down to the circuit board.

 

[alexfunari]

It's at the other end of your arrow & down a bit.Good luck Yes it is f9800

hahah i found it!!! Thanks guys, I'll report back!

 

[millereffect]

LP8545 where to get from

Hi everyone, I found the glitch!

The 4pcs of WLED driver (LP8545SQ) that I ordered from across the sea for $30 should arrive in a week or two. They are hard to find on our continent (Europe) but it seems like I wont need one and I also bought 3 spare pcs, so feel free to contact me, if you need one

Hello all,
does anyone of you know where to get the IC from National? I have search the internet but wasn't successful. I have the similare problems with my backlight on the A1278. The FSET input is shorted to ground internally. So I have to replace it.

Many thanks.

 

[Dadioh]

Hello all,
does anyone of you know where to get the IC from National? I have search the internet but wasn't successful. I have the similare problems with my backlight on the A1278. The FSET input is shorted to ground internally. So I have to replace it.

Many thanks.

I commonly buy parts from these companies. They have the parts listed but no stock.

http://search.digikey.com/scripts/DkSearch/dksus.dll?lang=en&site=US&KeyWords=LP8545&x=20&y=21

http://canada.newark.com/jsp/search...tions=false&ref=globalsearch&_requestid=71372

http://avnetexpress.avnet.com/store...art&catalogId=500201&langId=-1&storeId=500201