Just got my 6260.....some words.....

if u dont know what your doing, dont go inside, you need to know whats what and what are the parts that you should avoid. id test it using the fx loop to determine first wether its a pre or poweramp issue

if its neither, id have a look inside, search for signs of those melted molex connectors that they have issues with and any other electrical component!
 
so i tryed that trick to send signal into the return,but i wont have anything out from send...but i try normaly plug my guitar low gain input
and i get signal out from that preoutput thing :) but anyway i opened that amp and everything seem to me ok so i also try to "move" all tubes becouse if they are badly connected so after all that i put together amp and take first test "smoke" of it and worked well and that the end of that story and im soo relieved!