Just destroyed a brandnew Qpad MK-80

[Levial]

Hi Geeks,
just wanted to change the Blue LED from my MK80 to pink ones.
Used these here http://www.ebay.com/itm/130868524773?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1497.l2649
Used a Keyboard with blue LEDs cause the Voltage for the LEDs is the same.
Desoldered the old ones soldered the new ones without problems. Tested it with a single Pink LED and it worked. A little dark but it worked.
After installing the rest the new LEDs stay dark and the Keyboard is not recognised by the PC via Usb. PS/2 works still.
Desoldered every single LED, same error.
Any ideas what could have gone wrong here?

[joneslee85]

It seems to me you have short-circuit, what you could do desoldering-all and solder one by one, each comes with testing.

[Levial]

So after some Hours of testing als measuring I've found the problem.
I desoldered this little guy here:
http://cdn.pollin.de/article/big/G160076.JPG
After that I couldn't notice any difference except that my LEDs are working now.
I thougt that Thyristor is for the light-dimming but that works too after desoldering.
Maybe a broken LED toastet that thing?
Any ideas what else is it good for?

[regack]

Voltage regulator, mosfet... hard to tell just from the TO-220 package outline.

[Levial]

I just wonder that it seems to have no function. Everything works without that thing...
Eccept USB recognition, maybe it switches between USB+PS/2 mode? But that would make not much sense, a normal transistor could do that.
Electronic is a mystery sometimes