Eurocom laptop backlight repair (bypass?)

So, there was a small issue with my laptop.  It was dirty.  I cleaned the screen with glass cleaner and wasn’t too careful about where the liquid got.  Later that night the screen fizzles out.  In summary The not-water part of the cleaner corroded on the LCD connector on the display and no matter how much I cleaned it I couldn’t get it all functional.  I ordered a replacement panel (LTN156FL02-101) and a replacement cable (6-43-P7501-022-1C) from ebay and aliexpress respectively.  The panel came in first and I was excited to install it, in that excitement I tried seating the old laptop cable on the new (used) panel a couple of times and eventually I stopped getting backlight and smelled electronics burning (oops).

eurocom backlight circuit

Luckily this is a Eurocom, which means it’s a rebranded Clevo, which means I can get the schematics for it.  I have the schematics for the P775DM2(-G) and mine is a P751DM2-G and this section is the same between them.  Above is the chip that I found charred and destroyed.  The MTS3572G6 was burnt to a crisp.  I tried to order one but ebay had none, digikey had none, aliexpress had none, it seems to be a very specialized part (N-channel P-channel pair, like a darlington).  I could have gotten some similar FETs and bodged them back in, but after reviewing the circuit it seems that all this does is turn on the backlight.  Before I did this I had no idea if this would mean that it would always have the backlight on when the lid was closed, or other un-intended consequences.  But I also saw this:

edp circuit.PNG

This shows that the panel handles the brightness on its own, and even has a backlight-on line, the part of the circuit that fried seems to let the video card turn off the power to the backlight to save power (I’m guessing).  Based on all this bridging PJ45 would seem to fix my issue.  But if it happens again I’ll break something upstream and I don’t want that.  I could install a fuse at the jumper, but what reating? The burnt chip is good for… 20A? That won’t do (and I don’t believe it).  What are the ratings on the panel then.

backlight.PNG

Looks like 900mA.  I picked the next up size polyfuse (1100mA) and got to soldering.  It’s not pretty.

20190211_225919

That connector at the bottom is the graphics card socket, this all had to fit under the graphics card.  After re-assembling this thing for the tenth time in a week it boots up!  The new screen has a stuck pixel but that’s what I get for buying used instead of new.  The un-intended consequence is that I now have screen on boot every time.  Previously, when not in UEFI mode the screen would not light up if the laptop had been on recently (20 minutes or so).  I never found the root cause of this, but once windows 7 booted and the driver asserted the graphics card everything was fine.  Now it seems the display is always on for boot.  Don’t ask me why it used to have a cooldown time, I tried everything including removing the bios battery and resetting to factory defaults.  This jumper happened to fix all the problems I had with this laptop.

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