Hello!
I would ask you for a help. I'm looking to buy used gt-6 and I found one, quite cheap but there is one problem.
The guy is saying that when he is turning on a multi the screen display only squares. Probably the rest is working good, I would to ask him if everything other is working.
What do you think, is it very tough to repair this screen problem?
Had a similar issue with an old Quadraverb. The fix was a simple as ordering a new LCD and soldering it in.
That said, I don't know what's going on inside ur GT6, but if u could source a new LCD u might be able to replace it. Take a look inside and see how the screen is attached.
HTH