Don't know whether this helps, but I've found the fn+shift+F1 combination can be a bit temperamental! I routinely swap between V70 and the backlight or dual boot images and I have got used to the need to get the timing right. Although the nature of the SD card seems to be part of the problem according to some posts, I have found that pressing the on/off key followed AS QUICKLY AS POSSIBLE with the fn+shift+F1 combination works OK, but for some strange reason I have found pressing the Fn key followed by the Shift key followed by the F1 key, holding down each one very quickly after the other in that sequence (so all are held down eventually), sometimes makes the difference between the uImage flashing properly. The other thing to note is this takes only a second or so MAXIMUM. If it doesn't almost immediately (less than a second) show the new splash screen for the new uImage, it's probably failed - e.g if it goes to the rather psychedelic 60's fade!
Hope this helps someone!
