Dead Logic Board?

Jon

I got hold of a water damaged 15" macbook pro (mid 2010) and have just cleaned and reassembled it - the magsafe power light goes green and then amber (the battery charges & the battery indicator works). The problem is it doesn't show any signs of life when the power button is pressed (absolutely nothing!). Is this definitely a power button issue or could it also be the logic board at fault even though the battery charges?

Jon

Just an update if anyone actually reads this: turned out to be a keyboard issue after all - it's amazing how resilient the logic boards are especially after buying a badly water damaged unibody from a normal person (i.e someone without a tri-wing screwdriver) so the battery had been left in for about a week.

Anyway, I was wondering if anyone knows anything about the new LED backlights as the display backlight on this macbook is completely dead - everything else works fine. In the olden days you used to simply replace the inverter on the display, but I think whatever powers the LED backlight is now actually on the logic board and could have blown/fused. Anyone know what part this is exactly?

John

Hi Jon! Sorry for the delay getting back -- I've been away. I've also been able to recover several MacBook Pros simply by replacing the keyboard and power button. Personally, I'd go so far as to consider it a design flaw that you have to have a good keyboard in order to turn the computer on!

I'm not 100% sure about the backlight issue. I've found a number of machines with liquid damage right on the video connector on the board, and many with pins missing on the connector, and the video cable itself. Sometimes they have some black color to them, almost as if some pins on the connector have been burnt out. I've had some that ended up being the connector, and some that ended up being the screen assembly and cable (I've never gone so far as to replace a video cable). When it's been the connector, the machine has worked via external video...alas, it's a very unfortunate situation to have such a nice machine with a blown video connector on the board....

Obviously on these unibody machines there is only one video-related cable, and it terminates inside the hinge, so maybe replacing that (especially if there is visible liquid damage to it) would be a good start? I've only opened up a couple unibody screens, so I have to admit I'm not well versed on the intricacies of screen issues as far as these go, but if you figure it out I'd be very curious to hear!

Thanks again,

John

Jon

No worries thanks for the excellent reply. A few video pins had some black colour and the liquid got spilt right over the display connector, but I've cleaned it all up and I'm getting a perfect image when I shine a light on the screen (don't have an external video connector so can't test that) so I think it's just the backlight. I managed to get hold of a schematic diagram for the 2009 unibodies and the logic board design hasn't really changed for the mid 2010 models. Thanks to this brilliant thread on the topic (which also has a link to the schematic diagram) http://forums.macrumors.com/showthread.php?t=972699
I found out there's a tiny surface mount 2a fuse (smd 0402 32v) on the backlight circuit on the back of the logic board (non CPU side) for the 13" MBP and on the front of the logic board (CPU side) for the 15". After finally managing to find this (it has a little white dot on it and is TINY! ) I ran a multimeter test and sure enough the fuse has blown! Will order some today and hopefully get this part re-soldered and let you know the outcome. It seems quite a common thing to blow with liquid spills and lots of people on that forum have had success with it, so fingers crossed!

John

Wow, that is definitely a great finding! This is exciting...you're teaching me some good stuff! :-) It reminds me of a lot of the 12" iBook G4s, mostly the 1.2GHZ version I think -- they have a microfuse just like what you mentioned that controls the backlight. I've had several that have no backlight, but if you power on with a pair of metal tweezers or a paperclip touching either side of the microfuse, sure enough the backlight is on, and if you remove the tweezers, it goes off, etc. My problem with the G4s in this situation is that the microfuse is so darn small that I've ended up destroying about half of these machines in an attempt to solder the connection back together. I recently got a much better soldering iron (Weller WM120) and started using soldering paste, and that has improved my success rate considerably. You basically "sculpt" the paste (which is essentially solder in paste form) where you want it to be, and then one slight touch of a hot iron instantly heats it up and hardens it. Your plan to get an actual microfuse is probably the better way to go though, if you can manage to get the fuse on there...obviously, actually having a fuse is preferable to not...that way the board doesn't get blown if another similar incident occurs.

Anyway, very interesting stuff, and let me know how it goes!

Thanks,

John

Jon

Hi John sorry for the long update: had uni exams and it took forever to find and order the correct parts required without being a registered business! I ended up buying a very standard 20W iron (ANTEX) with a 0.1mm tip along with some 0.4mm solder (sorry for the metric system - from the UK) and a 10x eye loupe following the instructions here



Could have got some better equipment but only ended up spending about £30 ($50?) in total including the fuses which is not bad. Managed to solder everything correctly without frying the board - put it all back together and..... nothing changed: still no backlight

However, trying to diagnose what else it could be and since I now had an eye loupe, I thought i'd have another closer look at that LVDS cable - turns out you were rights after all about the connector: pins 38-40 are completely dead! Coincidentally these are exactly the pins where the backlight send circuit ends up (the one with the blown 2a fuse)!! So the fuse had blown AND the LVDS cable had burnt out! What are the odds!?! Furthermore the pins that control the actual video output (1-32 are still intact hence why I had a picture but no light.

Just about to order a new LVDS cable so hopefully that should sort everything out - I'll let you know how it all goes once it arrives from China.

Thanks for all the help - I'm getting this machine working even if it kills me!

John

Hi Jon! Sorry to hear the soldering didn't work. I always test beforehand by touching both ends with either side of a pair of metal tweezers...that way you can power on with the tweezers in place and tell beforehand if soldering would work. That's how I do it on the iBook G4s.

Anyway, good luck with the cable! I'll keep my fingers crossed! Like I mentioned, I've seen unibody MacBooks many with those pins burnt out, both on the video cable, and also the connector on the board. There must be a lot of power going through those specific pins, because they seem very susceptible to being fried by liquid damage or whatever. I've always given up at that point and assumed the board was irreparably damaged, so I'll be very curious to hear if you have success.

John