I'm having the same problem. I have an FBV express with my spider II 112 that worked great for a long time until a few years ago. I took the back cover off of the pedal to see if anything was fried and it's all good in there. Same with the amp head. nothing is obviously cooked or anything like that. And yes ive tried other cables haha. The jacks in both units are in tact,not bent or corroded or anything like that. I just kinda stopped caring about it for a while. But its becoming a problem as I am playing with some friends now and it a PITA to switch channels.
What happens is I will power up, and the tuner and all LEDs will light up for less then half a second. Then they ALL go out. And if you wait about five seconds the green LED for VOLUME on the "tweak" part will light up and stay lit. No channel LED will light up and the pedal for volume/wah control will not adjust the volume or switch to the wah selection with the click. And obviously the channel switches do nothing as none of them are lit up. Also will not switch to tuner feature. So its useless unless you like a little green light on a black box sitting in front of you while you play haha.
Any ideas? My knowledge of tiny little electronic things is extremely limited although I understand how electricity and components and such works. I dont know if it is a problem with the amp head or the switch itself. And i definitely dont know how to fix it without a little help haha.
Sorry for so many words, I just wanted to get all the details out there to give you guys a clear idea of what the problem is.. Thank you so much for any help.