Thanks for your very fast reply Dadioh.. I'm not too clued up with this! Can you please explain or point out where the enable pin is and which resistor it is on the circuit that you found had burnt out? It's the same board as the one you have attached a photo of previously where you showed the 27V test point.
Got a tip for us?
Let us know
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
MacBook Pro Unibody - No Backlight - Logic Board Question
- Thread starter Dadioh
- Start date
- Sort by reaction score
Thanks for your very fast reply Dadioh.. I'm not too clued up with this! Can you please explain or point out where the enable pin is and which resistor it is on the circuit that you found had burnt out? It's the same board as the one you have attached a photo of previously where you showed the 27V test point.
macbook A1278 LCD display no back light
@dadioh
> I go through your work on to restore the LED back light of
> Mac on macrumors forum, I am facing the same problem. After
> replacement of damage LCD of Macbook the back light never
> works, the display is there and now me working with external
> monitor. the detail of machine is here below,
>
> 1- LCD Screen : LP133WX2-TLG6 ( it is brand new screen) the
> previous version is LP133WX2-TLC2
> 2- Logic Board : 820-2327-A its printed on it, where
> as the part #661-4818
> 3- LVDS Connector: I-PEX
4- 2 GHZ processor
> Please indicate the fuse of LED back light on above logic
> board.
>
> Thanks
@dadioh
> I go through your work on to restore the LED back light of
> Mac on macrumors forum, I am facing the same problem. After
> replacement of damage LCD of Macbook the back light never
> works, the display is there and now me working with external
> monitor. the detail of machine is here below,
>
> 1- LCD Screen : LP133WX2-TLG6 ( it is brand new screen) the
> previous version is LP133WX2-TLC2
> 2- Logic Board : 820-2327-A its printed on it, where
> as the part #661-4818
> 3- LVDS Connector: I-PEX
4- 2 GHZ processor
> Please indicate the fuse of LED back light on above logic
> board.
>
> Thanks
Bought a MBP A1278 on Ebay with the problems. I thought it'd be an easy screen swap but I guess it's not.
I looked at the fuse and I bridged it with a screwdriver while my cousin powered it on. It sparked and smoked so I'm assuming there's more damage now. It does the same exact thing though. Any ideas? I can solder but not really really small components.
I looked at the fuse and I bridged it with a screwdriver while my cousin powered it on. It sparked and smoked so I'm assuming there's more damage now. It does the same exact thing though. Any ideas? I can solder but not really really small components.
Sparks and smoke means more damage unfortunately so you may want to consider turning this unit into a headless media center that doesn't require the LED display. Chances are whatever is blown will not be an easy fix particularly if you are not comfortable working with small parts.
Just a word of warning for those that are just bridging the fuse with solder or even temporarily with a screwdriver....
The reason that the fuse blew open was because there was a fault drawing more than 2A through that fuse. In the case of a liquid spill that "might" be a temporary short due to the presence of the liquid. Therefore cleaning the circuit of any residues may restore it to a good working condition and then replacing the fuse leads to a working backlight.
However, there is also a very good chance that the presence of liquid lead to another fault mode (like a short inside the WLED driver chip) that then blew the fuse. If this is the case (and there is a good chance it is) then the fault condition must be repaired before attempting to bridge the fuse. At least if you replace it with another fuse you are protected because the fuse will just blow again.
Let me suggest something. Before bridging the fuse make sure you clean the board really well with isopropyl alcohol (99% pure... not 70% rubbing alcohol). Then take an ohmeter (multimeter) and measure the resistance of both sides of the fuse to ground (pick one of the screw attachment points). If you are seeing a low value there (I am thinking less than 20 ohms) then STOP and look for the fault before continuing. Just bridging the fuse in this condition will cause fresh damage which is much harder to fix than a simple fuse.
I = V / R For V=12V and I>2A that means R < 6ohms will blow the fuse.
Please exercise caution guys and gals.
The reason that the fuse blew open was because there was a fault drawing more than 2A through that fuse. In the case of a liquid spill that "might" be a temporary short due to the presence of the liquid. Therefore cleaning the circuit of any residues may restore it to a good working condition and then replacing the fuse leads to a working backlight.
However, there is also a very good chance that the presence of liquid lead to another fault mode (like a short inside the WLED driver chip) that then blew the fuse. If this is the case (and there is a good chance it is) then the fault condition must be repaired before attempting to bridge the fuse. At least if you replace it with another fuse you are protected because the fuse will just blow again.
Let me suggest something. Before bridging the fuse make sure you clean the board really well with isopropyl alcohol (99% pure... not 70% rubbing alcohol). Then take an ohmeter (multimeter) and measure the resistance of both sides of the fuse to ground (pick one of the screw attachment points). If you are seeing a low value there (I am thinking less than 20 ohms) then STOP and look for the fault before continuing. Just bridging the fuse in this condition will cause fresh damage which is much harder to fix than a simple fuse.
I = V / R For V=12V and I>2A that means R < 6ohms will blow the fuse.
Please exercise caution guys and gals.
So I actually tried my screen in another MBP and it blew the fuse so the backlight in that one didn't work. Luckily it was under warranty so that's with Apple right now. I looked really closely at my LVDS cable and it looks damaged in the middle so it looks like that's the part which made the fuse blow. I didn't actually pull the board out all the way but I will once I get a chance and see how much damage is there . Apple said they would fix the computer for $250 out of warranty so I may head that route. It's still cheaper to fix it than buy a used one.
How hard is it to replace the LVDS cable in a MBP 13? I already pulled the screen, I just need to to know to pull the glass.
How hard is it to replace the LVDS cable in a MBP 13? I already pulled the screen, I just need to to know to pull the glass.
As you stated, replacing the LVDS cable requires pulling the glass. That is pretty tricky. There are guides available if you search (for example iFixit). The first 2 I tried I broke the glass. But that was with a large furniture stripper type of hot air gun. Now I have a soldering hot air gun and with a finer tip I was able to direct the airflow exactly where I wanted it. I finally got it on my third try.
Sorry for the delay getting to this. The enable is pin 4 and it should measure 3V if it is enabling the WLED driver. If you are measuring 0 volts then the WLED driver is not activating because it is not being enabled.
See attached. I can't remember exactly where the 301K and 100K resistors are located but I think they are close to pin 4.
Attachments
I am traveling at the moment and don't have access to a logic board to look at. If you can find some high resolution photographs of the front and back of the correct logic board then I can help you out now. Otherwise it will have to wait until I am home on the weekend.
Schematic of Macbook A1278
@Hi,
Can you please provide me the schematic of Macbook A1278, 13.3 inch.
Thanks
@Hi,
Can you please provide me the schematic of Macbook A1278, 13.3 inch.
Thanks
Hi Jankro,
Can you email me the schematic of the Macbook Pro? Because my son spill the water on the macbook and I cannot turn on at all, please help.
Can you email me the schematic of the Macbook Pro? Because my son spill the water on the macbook and I cannot turn on at all, please help.
@Hi,
Can you please provide me the schematic of Macbook A1278, 13.3 inch.
Thanks
I think you were looking for the fuse location for the Macbook Unibody 2008 aluminum non-PRO. It is on the back of the board so unfortunately you need to remove the logic board to test it. See attachment.
Attachments
Macbook A1278
@Dadioh,
Thanks for locating the fuse.
The voltage at Pin #3 of APP-1A is 0 and when the fuse is replaced it shows now 12.5v,but at pin # 21&22 still not get the desired 27v to lit the leds.Please specify the other check points.
Thanks
@Dadioh,
Thanks for locating the fuse.
The voltage at Pin #3 of APP-1A is 0 and when the fuse is replaced it shows now 12.5v,but at pin # 21&22 still not get the desired 27v to lit the leds.Please specify the other check points.
Thanks
OK. So at least you are now getting power to the WLED driver. But if it is still not boosting then there is another issue. It is possible that the chip is blown. One thing you can check is pin 5. That is the enable pin. It should be more than 3V.
Also, what are the voltages on the anode and cathode of the boost diode?
Macbook A1278 N-PRO Unibody 13.3 inch-Logic board
APP-1A pin 5 it is 1v instead of 3v.
The diaode which is in between I-PEX pin 21/22 and APP-1A,it is 12.5v from I-PEX side and at the other end it is 0v.
APP-1A pin 5 it is 1v instead of 3v.
The diaode which is in between I-PEX pin 21/22 and APP-1A,it is 12.5v from I-PEX side and at the other end it is 0v.
Macbook A1278 N-PRO Unibody 13.3 inch-Logic board
@dadioh,
any idea from where to get this wled.
@dadioh,
any idea from where to get this wled.
Hello to everyone! I'm a newcomer and a guy from El Salvador, Central America.
I come here, seeking your advice, as I have had a real trouble that plain sucks.
recently my hard drive stopped being readable, an after trying some other hd i figured out that it was the hard drive cable to the motherboard. I ordered it on ebay and problem solved.
And there I was placing the bottom case to start screwing it, suddenly an alluminum part of the bottom case touched the battery resulting in little sparks and the macbook shuttind down inmediatly. I turned it on again and there it was a pretty much dimmed led screen.
Everything is fine, i have used it with an external monitor, the led is fine you can see, barely but it works. It's just the backlight.
Could it be the fuse?? thanks!!
I come here, seeking your advice, as I have had a real trouble that plain sucks.
recently my hard drive stopped being readable, an after trying some other hd i figured out that it was the hard drive cable to the motherboard. I ordered it on ebay and problem solved.
And there I was placing the bottom case to start screwing it, suddenly an alluminum part of the bottom case touched the battery resulting in little sparks and the macbook shuttind down inmediatly. I turned it on again and there it was a pretty much dimmed led screen.
Everything is fine, i have used it with an external monitor, the led is fine you can see, barely but it works. It's just the backlight.
Could it be the fuse?? thanks!!
That is the problem. The non-Pro 13" unibody uses a custom part that seems to be Apple proprietary. AFAIK you would have to pull one off another logic board.
The Pro models use a part made by National Semiconductor that you can purchase from electronics resellers.
So this is a Macbook Pro 13" 2.26GHz (or 2.53GHz). Not the non-Pro (2.0 or 2.4GHz). There are differences in the logic board between the Pro and non-Pro.
If it is the Pro you will find a picture somewhere in this thread that shows where the fuse is located. Fortunately it is on the top side so you don't have to remove the logic board to test it. Measure it and report back.
Yes is the macbook pro 13 2.26.
So my logic board is the exact copy as the
https://forums.macrumors.com/attachment.php?attachmentid=285974&d=1305808864
I'm no expert in electronics, so I will request a friend help. So can you please point me out if I have to check all of those three things, and for what values am I looking in each of the three sections.
thanks
Just start by checking the fuse (it is identified in the picture that you linked). It should read a few ohms. If it shows many ohms (megaohms) then it is blown. Get a friend with a multimeter to help you. Unplug the battery first before probing on the board.
If the fuse is blown then you need to buy a new fuse and replace it. Some people on this thread have been shorting out the fuse to test it but I DO NOT recommend this since if there is another issue it will damage the logic board.
Good luck.
MacBookPro
I just got my MacBook Pro back from best buy. extended warranty work, I believe...I didn't have to pay but they said they had to replace the logic board which they said was a $950 part. Gotta love extended warranties. Is this a weakness in MacBook Pros? just wondering. I have another year warranty so hopefully its fixed.
I just got my MacBook Pro back from best buy. extended warranty work, I believe...I didn't have to pay but they said they had to replace the logic board which they said was a $950 part. Gotta love extended warranties. Is this a weakness in MacBook Pros? just wondering. I have another year warranty so hopefully its fixed.
In the battle of liquids vs. electronics... liquid usually wins
The effects of liquid on the circuit is not a fault of Apple. Any laptop that has liquid spilled on it will likely suffer the consequences whether it is built by Apple or Dell or whomever.
That being said, there are a couple of things that "might" make this worse for the case of Macbooks.
1) One of the things I love about Macbooks is the way they look. Nice clean lines. No ugly vents on the side or bottom. However, do you ever wonder where it gets its air for the fan? Through the keyboard. So if you spill on a working Macbook it sucks the liquid straight down onto the logic board. This may be less of a problem for a laptop that draws air from side vents.
2) The circuit that drives the LED's is 27V. That is a fair bit of voltage and in the presence of liquid that is where the excitement happens. However, I guess any LED display laptop will have the same sorts of voltages.
So to answer your question, I don't think this is really an Apple weakness. They can't really guard against liquid damage and keep the elegant design. Or maybe they can but at a cost. I think the number of actual failures is low compared to the number of Macbooks out there.
My $0.02 anyways
Macbook a1278 n-pro-logic board
@dadioh
Please check the photo and confirm it is a diode or resistor, as from the schematic i couldnt identify on the board.
@dadioh
Please check the photo and confirm it is a diode or resistor, as from the schematic i couldnt identify on the board.
Attachments
Is that connected to pin 9? If so there are 2 resistors hanging off pin 9 which is the VSEN signal for the WLED driver. This is how the driver knows what voltage it is putting out on the cathode of the boost diode. A 1.2Mohm in an 0603 package and a 71.5kohm in an 0402 package. That looks like an 0603 package so my guess is that is the 1.2Mohm resistor.
If this resistor is damaged then it would mess up the feedback loop and the WLED driver will probably stop boosting the voltage.
According to the resistor marking guidelines this is indeed 12 plus 5 zeroes = 1.2Mohm marking.
http://www.niccomp.com/Products/smt/NRCNRSNPartMarkingGuide.pdf