Hi all!

I`m new in the forum. I have a problem with an old game boy dmg that I bought from japan (I am from spain).

I fixed the dead vertical lines, and installed the backligth with the vibert mod. In this process, the rubber cable that links the two pcb`s, suffered (I was not careful enough) and the metal lanes, in the right side, was detached from the plastic part.

Now the screen works perfectly, but the left button is hold pressed. I tried to clean the contacts, but it is also pressed without the case and the rubbers.

Please. could anybody help me?

I'm trying to understand what you did here, do you mean you damaged the flat ribbon cable from the front circuit board?
It sounds like a short-circuit, as the button is kept pressed no matter what you do.

However, by looking at the schematic (here: http://gbdev.gg8.se/wiki/articles/DMG_Schematics) it seems like the B button should be affected too. Is this the case as well?

One common cause of this type of fault is that you might've briefly shorted two adjacent pins on the ribbon cable while inserting or removing it. In particular, the LCD drive voltage (-19 V) and the combined line used for reading the state of the left and B buttons. For this reason, you should NEVER insert or remove that ribbon while the power is on.

If this is the case, booth left and B have been permanently fried, and the CPU is basically unusable, unless you find an application where missing those buttons is acceptable. (Maybe external MIDI control?) If the B button is still functional you know that this is NOT the fault though, and you should look for a place where something connected to ground is shorted to something else.

Sorry for my bad english and thank you for your efforts to understand it.

I remember when I was installing the backligth I disconnected the cable with the console connected.

I guess I've learned a lesson.

Thank you very much for your help.