Mica and others have written about how problems with intermittent signal loss or excessive noise with the F-1X can often be cured by "exercising" the input and effects send/return jacks. By "exercise," we mean fighting corrosion in the jacks by plugging and unplugging a 1/4" plug in each jack 20 or 30 times every once and awhile.
I am a convert! Yesterday, I changed the power strip in my F-1X/SF-2 rig (which required unplugging the Superfilter from the effects send and returns on the F-1X). After I hooked everything back together I noticed a persistent high-pitched whine (right around 600 Hz) that wasn't affected by adjusting any of the gain knobs on either the preamp or Superfilter. When I took the Superfilter completely out of the circuit and used the F-1X by itself it was (as always) dead quiet. So, I figured something had gone wonky in the Superfilter. To be sure, I then took the F-1X out of the circuit and went bass- Superfilter- power amp - and, again, the rig was dead quiet.
I said a bad word (actually, two), indicating confusion. Then, light bulb! I remembered the jack exercise procedure and figured I would give it a try. After 25 plug/unplug cycles in the effects send and return jacks on the F-1X: voila! Everything was dead quiet once again.
Exercise is good!
You can read about the jack exercise procedure in the F-1X FAQ here:
http://club.alembic.com/index.php?topic=243.0