MacBook Pro Unibody - No Backlight - Logic Board Question

[Astroboy907]

I like that logic. As bad as the 3rd, 4th and 5th pins were destroyed on the cable, it makes sense that there might be something going on inside the connector on the board that i can't see. I'll try switching it out and see what happens. Thanks for the valuable input.

It's likely a short in the LVDS cable. I've had this happen before

It might also be a bent pin on the inside of the LDVS logic-side connector, if you have a microscope or good magnification it would be worth a look at that.

 

[funtotos]

no backlight 820-2936-A

Hello everybody!

I've been lurking in this thread for quite some time and I thank you all for this wonderful collection of information.

I myself got a damaged Macbook Pro 13" early 2011. The backlight is not working.
Perhaps you guys can help.

Macbook A1278 early 2011. 820-2936-A

What's wrong:
Liquid entered from the bottom of the Macbook. No backlight.

What I did:
Cleaned board with isopropyl.



I tested the display on a friends machine, and it works. the fuse is still intact.

I really need some pointers where to look at. I cannot afford replacement of the logic board

I have a usb microscope and can supply pictures if needed. Has anyone an idea what could be wrong? Or which components I should measure to start debugging the problem?

Thank you guys.

[/url][/IMG]

[/url][/IMG]

 

[cpufixer]

hi, Funtotos
The cap top left looks burnt, what usb cam do you have? I am looking for one where I can work under...

 

[bjf]

It's likely a short in the LVDS cable. I've had this happen before

It might also be a bent pin on the inside of the LDVS logic-side connector, if you have a microscope or good magnification it would be worth a look at that.

This is absolutely amazing how close this is to working and how much it still isn't. Everything now works perfectly except for the absolute slightest flicker in the backlight - barely perceptible. If I had to guess I would say it looks like the voltage is dropping by a tiny amount. It happens randomly, every 5 to 10 seconds or so.

I'm not sure if the LED driver could be at fault or if it's something smaller but this is what's been done so far:
- replaced the LVDS display cable (tested working on another A1466 also)
- replaced the display fuse - 3A.
- replaced the LVDS connector on the logic board
- cleaned board free of any corrosion and oxidation - no visibly blown components

MacBook Air 13" A1466 - Mid 2013 - Logic Board: 820-3437-A

At this point my soldering skills have exceeded my understanding of the inner workings of the board. Any help would be greatly appreciated. Thanks.

 

[Astroboy907]

This is absolutely amazing how close this is to working and how much it still isn't. Everything now works perfectly except for the absolute slightest flicker in the backlight - barely perceptible. If I had to guess I would say it looks like the voltage is dropping by a tiny amount. It happens randomly, every 5 to 10 seconds or so.

I'm not sure if the LED driver could be at fault or if it's something smaller but this is what's been done so far:
- replaced the LVDS display cable (tested working on another A1466 also)
- replaced the display fuse - 3A.
- replaced the LVDS connector on the logic board
- cleaned board free of any corrosion and oxidation - no visibly blown components

MacBook Air 13" A1466 - Mid 2013 - Logic Board: 820-3437-A

At this point my soldering skills have exceeded my understanding of the inner workings of the board. Any help would be greatly appreciated. Thanks.

Does it happen at full brightness or only at lower brightness levels?

 

[bjf]

Does it happen at full brightness or only at lower brightness levels?

It happens at all brightness levels. It's hard to tell but it might be doing it more when it's brighter. It's a very subtle flickering, so it's also possible that it's just harder to see it happening at lower brightness levels.

 

[Astroboy907]

It happens at all brightness levels. It's hard to tell but it might be doing it more when it's brighter. It's a very subtle flickering, so it's also possible that it's just harder to see it happening at lower brightness levels.

Any noticeable things awry on the board? Anything still burnt out?

 

[bjf]

Any noticeable things awry on the board? Anything still burnt out?

As it turns out, after further testing, nothing changed after switching out the LVDS connector on the logic board. The backlight is still intermittently cutting out and sometimes half, or all, of the array cuts out (sometimes every other LED.) And the flickering is also happening.

Nothing is visibly damaged on the board. The only visible issues were with the LVDS display cable and the backlight fuse. Both of those have been replaced.

I'm out of answers. It could be one of 10 or 20 different components. I just don't know the behaviors and functions of the components well enough to narrow this down. If anyone has a deeper understanding of these boards I would love to hear what you think. Thanks.

 

[kreliz]

I keep seeing these cap's on the wire diagrams marked with "CERM" as the temperature coefficient. But i can't find any on Digikey like it. Is it safe to grab a X7R or else in its place?

 

[bjf]

Well, I can add LED driver replacement to the list, and it's still doing the same thing. Unbelievable. Flickering backlight and parts of the LED array go out (usually every other LED on the left half of the screen.) I am out of answers.

- cleaned board free of any corrosion and oxidation - no visibly blown components
- replaced the display fuse - 3A.
- replaced the LVDS display cable (tested working on another A1466 also)
- replaced the LVDS connector on the logic board
- replaced LED driver

MacBook Air 13" A1466 - Mid 2013 - Logic Board: 820-3437-A

 

[BacklightFuse]

@BJF I havent see the schematics for this board but I'm guessing the enable voltage on the backlite driver is no enough hence the flickering screen, I would check the resistors values that make the voltage divider around the enable pin of your driver IC. If this is a water damaged board I would suggest checking all the caps in the T29 circuit as well.

Well, I can add LED driver replacement to the list, and it's still doing the same thing. Unbelievable. Flickering backlight and parts of the LED array go out (usually every other LED on the left half of the screen.) I am out of answers.

- cleaned board free of any corrosion and oxidation - no visibly blown components
- replaced the display fuse - 3A.
- replaced the LVDS display cable (tested working on another A1466 also)
- replaced the LVDS connector on the logic board
- replaced LED driver

MacBook Air 13" A1466 - Mid 2013 - Logic Board: 820-3437-A

 

[BacklightFuse]

I had the same problem with my mobo 820-2936b . 12volts at both sides of the fuse and 3volts at the enable pin of the lp8550. I had IC replaced and everything when back to normal. Hope this helps.

BTW you'll need a hot air station to remove the sucker and kapton tape to protect the surrounding area.

Hello everybody!

I've been lurking in this thread for quite some time and I thank you all for this wonderful collection of information.

I myself got a damaged Macbook Pro 13" early 2011. The backlight is not working.
Perhaps you guys can help.

Macbook A1278 early 2011. 820-2936-A

What's wrong:
Liquid entered from the bottom of the Macbook. No backlight.

What I did:
Cleaned board with isopropyl.



I tested the display on a friends machine, and it works. the fuse is still intact.

I really need some pointers where to look at. I cannot afford replacement of the logic board

I have a usb microscope and can supply pictures if needed. Has anyone an idea what could be wrong? Or which components I should measure to start debugging the problem?

Thank you guys.

 

[Dadioh]

@BJF I havent see the schematics for this board but I'm guessing the enable voltage on the backlite driver is no enough hence the flickering screen, I would check the resistors values that make the voltage divider around the enable pin of your driver IC. If this is a water damaged board I would suggest checking all the caps in the T29 circuit as well.

My thoughts as well. Assuming that the LP8550 solder balls are all making good contact after replacement then I suspect some bad solder joint in the surrounding components. When you replaced the 8550 I suppose it would have reflowed the solder on the resistors and caps surrounding the part. Maybe really careful inspection under high magnification at an angle (rather than straight down view) may identify a bad connection on one of the components?

Worst case, maybe removing, verifying, and replacing the resistors and caps one at a time. Painful process though :-(

 

[bjf]

@BJF I havent see the schematics for this board but I'm guessing the enable voltage on the backlite driver is no enough hence the flickering screen, I would check the resistors values that make the voltage divider around the enable pin of your driver IC. If this is a water damaged board I would suggest checking all the caps in the T29 circuit as well.

It's always felt like a voltage issue but I've just had no idea of where to start. The LED driver seemed like it might be a possible cause of that problem.

I have the schematics but not the brd file so I'm not sure if I'll be able to track down those resistors. I'm also not familiar with the T29 circuit but I'll dig around and see if I can figure it out. Thanks for the info. I'm completely stalled so it's really helpful.

----------

My thoughts as well. Assuming that the LP8550 solder balls are all making good contact after replacement then I suspect some bad solder joint in the surrounding components. When you replaced the 8550 I suppose it would have reflowed the solder on the resistors and caps surrounding the part. Maybe really careful inspection under high magnification at an angle (rather than straight down view) may identify a bad connection on one of the components?

Worst case, maybe removing, verifying, and replacing the resistors and caps one at a time. Painful process though :-(

I'm assuming I got the solder balls down. It looks good from all sides under a microscope and it's doing the same exact thing it was doing before. It's a possibility they're not all down, but I'm not sure how I would check that and I'll have to go with the assumption they are.

I'll try another visual inspection of the board from all angles. Thanks for all the help.

 

[BacklightFuse]

send me a PM with your email and i'll forward the boardview for your patient.

It's always felt like a voltage issue but I've just had no idea of where to start. The LED driver seemed like it might be a possible cause of that problem.

I have the schematics but not the brd file so I'm not sure if I'll be able to track down those resistors. I'm also not familiar with the T29 circuit but I'll dig around and see if I can figure it out. Thanks for the info. I'm completely stalled so it's really helpful.

----------



I'm assuming I got the solder balls down. It looks good from all sides under a microscope and it's doing the same exact thing it was doing before. It's a possibility they're not all down, but I'm not sure how I would check that and I'll have to go with the assumption they are.

I'll try another visual inspection of the board from all angles. Thanks for all the help.

 

[Astroboy907]

Editable wikis have been rolled out... should this become a wiki?

 

[dieett]

Mbp a1271

Hello macrepair

The logic board in question is from a MacBook Pro 17" (2009) A1297 with part number 820-2610-A.

I think the part is a transistor at position Q7790 and shows part 796Z.

Does anyone know where I can find schematics for logic boards? I have seen a few paid sites but not sure how legitimate they are?

maybe it helps?

If necessary I can also send the brdFile.
I got just 10 copies FDC796N from china!

many greetings from
germany

 

[macrepair]

I have a MacBook Pro 17" A1297 (2010) with logic board 820-2849-A.

The backlight stopped working a few months ago and after replacing fuse has worked perfectly.

But now the backlight has stopped working again and have found the fuse is still good.

I have been searching for WLED driver but not sure this is it with part number M34845B 4DRUY?

There is currently 8.4V on backlight fuse and 8.2V on LVDS connector on the 3 backlight pins, after powering on. So seems like voltage is not being boosted? Not even sure if this is the WLED at fault?

Any help greatly appreciated

 

[macrepair]

I have a MacBook Pro 17" A1297 (2010) with logic board 820-2849-A.

The backlight stopped working a few months ago and after replacing fuse has worked perfectly.

But now the backlight has stopped working again and have found the fuse is still good.

I have been searching for WLED driver but not sure this is it with part number M34845B 4DRUY?

There is currently 8.4V on backlight fuse and 8.2V on LVDS connector on the 3 backlight pins, after powering on. So seems like voltage is not being boosted? Not even sure if this is the WLED at fault?

Any help greatly appreciated

I'm fairly certain this is the WLED driver - have found that pin 24 on the QFN package is connected to LVDS backlight pins and is outputting only just over 8V but should I believe should be around 40V .

I have no idea who manufactures this chip or where I can source a replacement.

Also not sure why this has failed as don't believe this has had any liquid spillage in the past.

Hope someone can help!

 

[macrepair]

I'm fairly certain this is the WLED driver - have found that pin 24 on the QFN package is connected to LVDS backlight pins and is outputting only just over 8V but should I believe should be around 40V .

I have no idea who manufactures this chip or where I can source a replacement.

Also not sure why this has failed as don't believe this has had any liquid spillage in the past.

Hope someone can help!

After a bit more research have found this QFN is made by Freescale.. http://www.freescale.com/

Not sure where to buy a replacement though.. Hopefully they can help.

 

[macrepair]

After a bit more research have found this QFN is made by Freescale.. http://www.freescale.com/

Not sure where to buy a replacement though.. Hopefully they can help.

http://www.freescale.com/files/analog/doc/data_sheet/MC34845.pdf?&Parent_nodeId=&Parent_pageType=

 

[greekhero]

Holy cow! guess what, my macbook is back on duty

i ordered the samples from NS and it took only 2 days shipping from singapore to germany with UPS Worldwide express. Thanks National

only thing i experienced is: the new chip does not have dithering, so you see the dimming steps. but thats a flaw i can live with.

thanks Dadioh for your support. and if anyone ever needs a LP8550 do not hesitate to contact me. or otherwise just get some samples from NS

Hi naKrull or anyone else who reads it,

A while ago you were able to successfully replace the DSBGA package LP8550. Do you remember how you did it? Can you please verify that the steps below are what you followed?

1. Remove the chip using heatgun.
2. Clean the pads/remove all solder and apply flix
3. Question: Did you apply some soldering Paste at this stage to the pads or to the LP8550 pins? OR Did you apply any solder on the pads?
4. You placed the new chip on the pads and applied heat using the heatgun using instructions from Dadioh.

My question really is do we need to add any type of paste or the LP8550 pins already have solder on them? I am really stuck at this and any help you can provide would be appreciated.

Thanks!

 

[Astroboy907]

Hi naKrull or anyone else who reads it,

A while ago you were able to successfully replace the DSBGA package LP8550. Do you remember how you did it? Can you please verify that the steps below are what you followed?

1. Remove the chip using heatgun.
2. Clean the pads/remove all solder and apply flix
3. Question: Did you apply some soldering Paste at this stage to the pads or to the LP8550 pins? OR Did you apply any solder on the pads?
4. You placed the new chip on the pads and applied heat using the heatgun using instructions from Dadioh.

My question really is do we need to add any type of paste or the LP8550 pins already have solder on them? I am really stuck at this and any help you can provide would be appreciated.

Thanks!

I would assume a BGA would need reballed?

 

[phong88]

I have a problem with my A1286 Mid 2010 MBP backlight. I can see faint image if I shine a flashlight and external monitor works just fine.

I measured the fuse and it seems to be fine, the only thing I can find wrong is there is no 3V on the enable pin (pin4). Also there is no voltage across the diode (with a "76" marking). There is 12V across the 330K resistor.

Where do I start to look for what's wrong? Is it the L8545SQ chip or is it something else? Thanks.

 

[ZZZAC]

I have a problem with my A1286 Mid 2010 MBP backlight. I can see faint image if I shine a flashlight and external monitor works just fine.

I measured the fuse and it seems to be fine, the only thing I can find wrong is there is no 3V on the enable pin (pin4). Also there is no voltage across the diode (with a "76" marking). There is 12V across the 330K resistor.

Where do I start to look for what's wrong? Is it the L8545SQ chip or is it something else? Thanks.

The purpose of the two resistors on the enable pin of the WLED chip is to divide the voltage from 12v to 3v so to enable the output of the WLED
If either of these resistors have failed it wont enable the wled thus not enabling the backlight.

Check the resistance of the two resistors on the WLED enable line, one of them may be open. its best to remove them to test them, i have had some confusion with false readings on the resistors (mainly the 330k resistor)

Basically if you have no 3v to the wled one of those resistors has probabley failed. if you replace them and see no change id suspect the wled itself. (recently had a MBA where the wled being bad would cause the enable resistors to nly read about 20k, replacing the horrid bga wled resolved it)

----------

I would assume a BGA would need reballed?

nah its tiny, plus most of the time these BGA's fail theres no going back, unlike a standard chip that would fail over time due to bad solder, these usually go bad due to liquid or other damage that would render the chip completely useless.

you can buy new chips and there DIRT cheap they come with solder balls attached, then its just a case of
removing the old chip
very carefully cleaning the pads
attempting to align the new cheap
and of course re soldering it. they tend to drop into place youl know when its reflown.

My only caution is if your not good at soldering maybe dont go over the pads with wick, pads under this bga aswell as under the smc chip are fairly delicate, more likely than pulling one you'll scratch mask away from a trace and its usually no problem.

----------

I'm fairly certain this is the WLED driver - have found that pin 24 on the QFN package is connected to LVDS backlight pins and is outputting only just over 8V but should I believe should be around 40V .

I have no idea who manufactures this chip or where I can source a replacement.

Also not sure why this has failed as don't believe this has had any liquid spillage in the past.

Hope someone can help!

Few things to check.
Do you get voltage across the diode? (this rules out the power enable fets that come just after the fuse)

Have you checked two resistors, they go to the enable pin of the wled, if either resistor is open the wled chip wont be enabled.