MacBook Pro Unibody - No Backlight - Logic Board Question

[udawat]

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.

Hello mryallups,
You seem to have the same problem as i do. I am facing the exact same problem. I got a new screen and connected it through the old LVDS cable and it didn't worked. Now, I had the opportunity to check the same screen on my friends MacBook Pro; and found that the new screen worked with my old LVDS cable (the whole upper body was connected to the other MBP). I am confused that the method mentioned by Dadioh is for us or not (Is it really the Backlight issue!)

 

[Dadioh]

Hello mryallups,
You seem to have the same problem as i do. I am facing the exact same problem. I got a new screen and connected it through the old LVDS cable and it didn't worked. Now, I had the opportunity to check the same screen on my friends MacBook Pro; and found that the new screen worked with my old LVDS cable (the whole upper body was connected to the other MBP). I am confused that the method mentioned by Dadioh is for us or not (Is it really the Backlight issue!)

The new display works with the old LVDS cable on another Macbook. Therefore New display is good and Old LVDS cable is good. That same combo does not work on your macbook logic board. Therefore the logic board is the problem. Do you have a dim image on your display (shine a flashlight in the middle while booting and you should see the apple logo). If not then it is more than just the backlight.

 

[millereffect]

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

Thank you Dadioh for your help! But I already looked at these suppliers and could not find any stock either.

Vyrcoop was stating in one of his previous posts that he has ordered some spare parts of exactly this device. I cannot get in touch with him right now because of the forum rules for newbies. Could you (Dadioh) please do me the favour and send him a message that there is somebody in the forum who would kindly need his help.

That would be great!

 

[udawat]

The new display works with the old LVDS cable on another Macbook. Therefore New display is good and Old LVDS cable is good. That same combo does not work on your macbook logic board. Therefore the logic board is the problem. Do you have a dim image on your display (shine a flashlight in the middle while booting and you should see the apple logo). If not then it is more than just the backlight.

Hi,
I don't have a bright torch light to test but from what i used (an ultra bright LED), i could not see the apple logo. Also, the Display has a dim light which is always on (no image!) when the macbook is started and it can be controlled by F1 and F2 keys but it does not display anything. Help me figure out the problem!!
PS: In the process of DIY Repair, while changing the displays, i messed up with the Bluetooth/Camera cable and they stopped working.

 

[Dadioh]

Hi,
I don't have a bright torch light to test but from what i used (an ultra bright LED), i could not see the apple logo. Also, the Display has a dim light which is always on (no image!) when the macbook is started and it can be controlled by F1 and F2 keys but it does not display anything. Help me figure out the problem!!
PS: In the process of DIY Repair, while changing the displays, i messed up with the Bluetooth/Camera cable and they stopped working.

That sounds as if the video signal is not getting through the LVDS cable to the display but the backlight is. Examine the cable connection very closely to see if there is damage. They are very delicate.

 

[Dadioh]

Thank you Dadioh for your help! But I already looked at these suppliers and could not find any stock either.

Vyrcoop was stating in one of his previous posts that he has ordered some spare parts of exactly this device. I cannot get in touch with him right now because of the forum rules for newbies. Could you (Dadioh) please do me the favour and send him a message that there is somebody in the forum who would kindly need his help.

That would be great!

PM sent to vrcoop.

 

[vyrcoop]

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.

Hey, I ordered from here: http://avnetexpress.avnet.com/store...=lp8545&N=0&Ne=100000&action=products&x=0&y=0

The first from the list - LP8545SQE - 396 in stock (I'm not sure what's the difference or if there is any between this and the 'SQX' version)...
If you're in Europe, you might want to wait until it arrives to me and I can resend it. However when I found that this component wasn't the part of my problem I changed the shipping service to a cheaper one (I used a freight forwarder), so it will probably take some week or two before I get it.

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

Thanks

 

[westbound]

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

View attachment 296801

I tested what I think is the fuse and it seems to be ok. The backlight now tends to flash momentarily during start-up, so maybe the problem may lie somewhere else.
Any clue where I should look??

 

[Dadioh]

I tested what I think is the fuse and it seems to be ok. The backlight now tends to flash momentarily during start-up, so maybe the problem may lie somewhere else.
Any clue where I should look??

So that means one quick flash during startup and then no further flashes? If it is having sporadic flashes afterwards it suggests an intermittent connection somewhere. If it flashes once during startup and never again it suggests that the circuit tries to start but the feedback shuts it down. i.e. there is a feedback on the voltage output of the WLED driver and if it goes too high it may shut down for self preservation. If that is the case then looking at that feedback would be a good starting point. Do you have some sort of electronics experience to troubleshoot this if you had a schematic?

 

[millereffect]

Hey, I ordered from here: http://avnetexpress.avnet.com/store...=lp8545&N=0&Ne=100000&action=products&x=0&y=0

The first from the list - LP8545SQE - 396 in stock (I'm not sure what's the difference or if there is any between this and the 'SQX' version)...
If you're in Europe, you might want to wait until it arrives to me and I can resend it. However when I found that this component wasn't the part of my problem I changed the shipping service to a cheaper one (I used a freight forwarder), so it will probably take some week or two before I get it.

Thanks

Thank you for telling me that you have found them at Avnet. Yes, I am also living in Europe (Germany). So if the part does arrive just give me a sign and I will provide you my shipping address and tell me how much you will charge for the device/s plus shipping. If possible maybe you could also provide me your email address so that I can contact you directly without having to post the next steps here in the forum.

By the way, what is your problem if it's not the backlight driver IC. Maybe I can help.

Many thanks again!

 

[westbound]

So that means one quick flash during startup and then no further flashes? If it is having sporadic flashes afterwards it suggests an intermittent connection somewhere. If it flashes once during startup and never again it suggests that the circuit tries to start but the feedback shuts it down. i.e. there is a feedback on the voltage output of the WLED driver and if it goes too high it may shut down for self preservation. If that is the case then looking at that feedback would be a good starting point. Do you have some sort of electronics experience to troubleshoot this if you had a schematic?

I have very little electronics experience,but eager and willing to learn.

 

[westbound]

My experience is limited to swapping out logic boards and minor soldering.
When i first got this wd unit the backlight flashed violently for over an hour before it eventually stop working.

 

[destic]

Macbook A1342

For all Polycarbonate Macbook A1342 owners: I have marked the Fuse and the LED Driver on the following images.
http://imageshack.us/photo/my-images/839/fuses.jpg/
http://imageshack.us/photo/my-images/189/leddriver.jpg/
The LED Driver has the following printed on it:
MC34834
4GROAJ
Its Datasheet can be obtained here:
http://www.freescale.com/files/analog/doc/data_sheet/MC34845.pdf
my only problem is that there are 10 variants on digikey:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556628&k=mc34845
They differ in their Frequency. Does anybody here know how I can determine the desired frequency for my a1342 Macbook?

 

[westbound]

For all Polycarbonate Macbook A1342 owners: I have marked the Fuse and the LED Driver on the following images.
http://imageshack.us/photo/my-images/839/fuses.jpg/
http://imageshack.us/photo/my-images/189/leddriver.jpg/
The LED Driver has the following printed on it:
MC34834
4GROAJ
Its Datasheet can be obtained here:
http://www.freescale.com/files/analog/doc/data_sheet/MC34845.pdf
my only problem is that there are 10 variants on digikey:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Cat=2556628&k=mc34845
They differ in their Frequency. Does anybody here know how I can determine the desired frequency for my a1342 Macbook?

Thank you very much for the info.You guys are great. This really helps.
As far as I can tell the fuse is ok(ohm test) and I have 12v on both sides of the fuse. Where should I be checking next?

 

[Mothsmusik]

OK for all the people with no backlight on a macbook pro 15" unibody.

first of all thanks to the man with the schematic....
I take it you have checked the flurecent and inverter allready and both are ok.
on the logic board there is a fuse that supply's the voltage/ currant to the backlight circuit...its F9800.Its located on the board near the botom of the left fan on the component side of the board.(same side that has the cpu and gpu on it).

the fuse is a smd and its white with just a dot on it.get your multimeter and if its open circuit thats you problem.
got mine fixed today...

If you need a hand then drop me a line and i will try to see what i can do...

Had to share this as it took me a good day to put right,,,

good luck.

componentfix

Hi there,

This has been a very informative thread, so I thought I'd ask if anyone has any experience with power inverters?

Backstory: 2010 Macbook Pro 13 had a small liquid spill on it and 2 Mac Store tests have concluded that everything inside is perfectly fine, but the Power Inverter on the Logic board needs to be replaced... The Laptop is still under warranty, but that does not cover accidental liquid damages

Does anyone know where I can buy a power inverter either new or gently used? Is this a good DIY project for an electronics tinkerer like myself?

If any of you have experience with this problem or think you might be able to help/offer some valuable insights, please let me know asap!

 

[Mothsmusik]

Logic board power inverter for 2010 Macbook Pro 13...

Hi there,

This has been a very informative thread, so I thought I'd ask if anyone has any experience with power inverters?

Backstory: 2010 Macbook Pro 13 had a small liquid spill on it and 2 Mac Store tests have concluded that everything inside is perfectly fine, but the Power Inverter on the Logic board needs to be replaced... The Laptop is still under warranty, but that does not cover accidental liquid damages

Does anyone know where I can buy a power inverter either new or gently used? Is this a good DIY project for an electronics tinkerer like myself?

If any of you have experience with this problem or think you might be able to help/offer some valuable insights, please let me know asap!

 

[destic]

http://cgi.ebay.de/ws/eBayISAPI.dll?ViewItem&item=250800543895

as far as I know, there is no power inverter in the 2010 Macbook, perhaps they mean the DC-In Board. Lately I could reanimate a completely dead macbook just by replacing this board.

 

[udawat]

That sounds as if the video signal is not getting through the LVDS cable to the display but the backlight is. Examine the cable connection very closely to see if there is damage. They are very delicate.

I connected the LVDS cable to the LCD only (not the upper lid) and found out that the backlight is on (tiny white LEDs glowing at the back contour of the screen). Now, the question is - Why is the Video signal not coming through the LVDS cable? I have the schematic but not able to understand it completely. Could it be related to WLED driver or the Fuse?

 

[destic]

Thank you very much for the info.You guys are great. This really helps.
As far as I can tell the fuse is ok(ohm test) and I have 12v on both sides of the fuse. Where should I be checking next?

you should now check every pin from your LED Driver with a multimeter set on Continuity (beeps when a circuit conducts). Put the black tip where the logic board has blank metal which is normally connected to the screws and with the red tip try to check every pin of your LED Driver. According to the Datasheet I provided above there should only 6 pins be connected to ground(Multimeter then beeps) if there are more, your LED Driver is broken, otherwise something other than the LED Driver or the Fuse is broken(some resistor or conductor), to answer that question, one needs a circuit diagram.

 

[Dadioh]

I connected the LVDS cable to the LCD only (not the upper lid) and found out that the backlight is on (tiny white LEDs glowing at the back contour of the screen). Now, the question is - Why is the Video signal not coming through the LVDS cable? I have the schematic but not able to understand it completely. Could it be related to WLED driver or the Fuse?

The backlight driver and the video signals are completely separate from one another so you need to focus on the schematic where the data signals are generated and passed to the LVDS connector.

 

[westbound]

you should now check every pin from your LED Driver with a multimeter set on Continuity (beeps when a circuit conducts). Put the black tip where the logic board has blank metal which is normally connected to the screws and with the red tip try to check every pin of your LED Driver. According to the Datasheet I provided above there should only 6 pins be connected to ground(Multimeter then beeps) if there are more, your LED Driver is broken, otherwise something other than the LED Driver or the Fuse is broken(some resistor or conductor), to answer that question, one needs a circuit diagram.[/


Does the computer need to be on to conduct these tests? Because the board would have to be removed to gain access the driver.

 

[udawat]

The backlight driver and the video signals are completely separate from one another so you need to focus on the schematic where the data signals are generated and passed to the LVDS connector.

I have done my homework. I spent hours understanding the schematic (Macbook Pro Late 2008 A1286 model) and traced the LVDS Data signals back to the (MCP79) nVidia GeForce 9400M Chipset (thats a long way). Learnt a lot - LVDS was developed by National Semiconductors and stands for "Low Voltage Differential Signaling".

If you have that schematic, on page 77, LVDS_EG_A_DATA and LVDS_EG_B_DATA signals are generated from the GPU (U8000).
Page 83 - The Signals go to U9600 and then LVDS_A_DATA and LVDS_B_DATA are generated (LCD_PWR_EN is also generated).
Page 80 - LVDS Transmitter Termination - There is a set of (3x8 = 24) resistors (U9200) which change the signals to LVDS_CONN_A_DATA and B_DATA.
Page 79 - Finally, they end up in the LVDS connector on the top right of the motherboard.

So, now the question is - In between this journey, i have to find the source of my problem going from theory to practical. How can you help me?

My case history is at: Post 195

 

[Dadioh]

Does the computer need to be on to conduct these tests? Because the board would have to be removed to gain access the driver.

Definitely not. These are resistance measurements so they need to be done with no voltage present on the board. So pull the logic board out and take the measurements.

 

[Dadioh]

I have done my homework. I spent hours understanding the schematic (Macbook Pro Late 2008 A1286 model) and traced the LVDS Data signals back to the (MCP79) nVidia GeForce 9400M Chipset (thats a long way). Learnt a lot - LVDS was developed by National Semiconductors and stands for "Low Voltage Differential Signaling".

If you have that schematic, on page 77, LVDS_EG_A_DATA and LVDS_EG_B_DATA signals are generated from the GPU (U8000).
Page 83 - The Signals go to U9600 and then LVDS_A_DATA and LVDS_B_DATA are generated (LCD_PWR_EN is also generated).
Page 80 - LVDS Transmitter Termination - There is a set of (3x8 = 24) resistors (U9200) which change the signals to LVDS_CONN_A_DATA and B_DATA.
Page 79 - Finally, they end up in the LVDS connector on the top right of the motherboard.

So, now the question is - In between this journey, i have to find the source of my problem going from theory to practical. How can you help me?

My case history is at: Post 195

Good work. I will have a look when I get a chance and see if there are some obvious troubleshooting tips. External display works so I suspect it is not the 9400m. The fact that it was oscillating back and forth in your description may suggest some sort of intermittent connection. Check the liquid spill areas. Sometimes the liquid causes corrosion on the ends of the resistors and caps so they look like they are connected but not actually since the end solder connection rots away. Good starting point anyways. If you can get access to a microscope it would really really help. it is a whole different world when looking at these things under a microscope.

Given the history you may very well spot the problem visually.

Good luck.

 

[bjf]

MacBook Pro 13" Not Charging

I have a MacBook Pro 13" that lost the backlight during a spill but also lost the ability to charge. The computer works fine on battery but won't charge. Most of the posts in this thread are related to the backlight issues common with spills but I haven't seen any mention of power issues. Has anyone tackled anything like this?