Thursday, November 13, 2014

Lenovo IdeaCentre A600 Restoration - MXM to Onboard Conversion

Continued from the previous post

Quite a lot of things needed to be changed to get the Intel GPU up and running.
  • Removing the resistors that disabled the onboard graphics and set up the MXM as default
  • Reconfiguring the clock generator (moving resistors and jumper links) to output the necessary clocks for the onboard GPU
  • Moving the backlight logic control circuitry (a few transistors and passives) from the MXM side to the onboard one (which also happened to the one the other side of the motherboard)
  • Moving the LVDS connector


Backlight control circuit components in their new location



I never invested into any modern soldering tools so this is going to be entertaining.
Behold my extremely professional tools made especially for the LVDS connector.



Two relics and some bent copper wire



Connector in MXM location


Connector removed



Pads cleaned



Connector in on-board location

 
Note how the sticker magically repaired itself (I'm cheating because I didn't take enough pictures)

Let it be known that I have since bought a proper soldering iron (though no tips that would've helped me with this...)

I did consider just buying and installing another connector instead of moving the original..It's a Hirose DF13-40DP-1.24V-55. I decided against it due to minimum order quantities and shipping costs. There's no way to keep both options alive anyway, so there really isn't much of a point. One of the connectors would be useless without moving a significant amount of components around.

So after doing all that (which took like a week of working on it after work) I had a machine that.. still wouldn't show anything on the display.
Everything seemed fine in dmesg now. The error message was gone and even the panel resolution was detected properly but the backlight just wouldn't turn on.

There is a small board with a capacitive sensor array and a microcontroller in the plastic frame that the protective glass was glued onto. You could touch the glass above it and it would light up to reveal 4 "buttons" (backlight controls and optical drive eject). I didn't have this board connected while testing which turned out to be a mistake. Embarrassingly enough it took me a few days to figure this out.
The board seems to be responsible for the backlight PWM control signal so without it there's no backlight.

After hooking it up I was greeted with a different problem. The inverter shut down after 2 seconds and would not start back up until a power-cycle. This is not a good sign at all and usually points to either the CCFL tubes or the inverter transformers being bad. Urgh!

At this point I was getting pretty annoyed with the project so I left it alone for a couple of weeks contemplating whether I should just toss the whole thing.

In the end I took one of my monitors apart and hooked up the CCFL tubes to it's inverter to make sure they weren't bad. They weren't, so the issue was on the inverter board.

DARFON 4H.V1561.091 inverter board


Not the transformers though, they checked out.
No ic pinout, no datasheet, no schematic. I painstakingly de-soldered and tested 90% of the components of the board separately. Everything checked out.
The least likely suspect - the controller chip - was looking really suspicious at this point. The only problem being that this chip (LX6512CPW) in this package (TSSOP) is simply not sold anywhere.

Replacement inverter boards cost as much as I paid for the whole machine.
Do I give up and hack in a universal inverter board after wasting so much time on this? There's no way it would fit into the case and brightness controls wouldn't work properly. Urgh!

As a final Hail Mary attempt I contacted MicroSemi, explaining the situation. I didn't think they'd really bother with a samples request for a discontinued product used in one-off repair by a hobbyist.


They did!


Brand new LX6512CPW sample in nice plastic case


It works!



Wooo-- wait.. why does that picture look weird?

Hrmm?


Some pixels are the wrong color...

I double and triple checked the LVDS connector visually. Couldn't see anything wrong. Continuity checked the cable, checked out.

After the fourth disassembly and spending an hour looking at it with a magnifying glass and poking at it with a multimeter while double-checking the schematics I finally found it. Barely visible adjacent pin short at the very base of the LVDS connector. @#!$!@%

Couldn't even get it out with solderwick so I ended up having to break it apart with a needle ...

But then it finally.. finally worked.


So now I had a functional machine converted to use the onboard graphics with a repaired inverter. Nice!
Slight problem... I can't use a dual monitor setup with this machine
... or can I?

Check the next post to find out.

3 comments:

  1. You must have found a kindred spirit at MicroSemi because that is a very nice case you got :-) Awesome work on the repairs!

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  2. It's amazing! Great job, thanks for sharing.

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  3. Thumb up for the repair and second thumb up for MicroSemi being so nice to send the chip.

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