Or do you just put the back back on and leave as is. I just cleaned the nasty rotting foam out of my MXR Dyna Comp and am wondering if I need to replace it or not.
Cleaning the crumbly foam out is a good idea, while just slapping the back on afterwards is not. You have to have something covering the back of the board, or you risk shorting stuff out. Most of the MXRs came with a stiff paper bit to cover the back of the board, and I'll usually re-use that. Then I will also want something to cover the component side. I usually make up something that will wrap around the board (stopping it from knocking about inside the box and shorting out against the bottom plate), just to be safe.
Stupid question, but why did MXR go with foam when everyone else seems to have found a way to mount the board to the box in some way? Always seemed a little silly to me to have the board flopping around even if it is wrapped in foam.
I recently got a Phase 45 and the foam was a combination of crumbling apart and stuck to the parts. I cleaned it best I could and put some thin packing foam around it.
What is that stuff anyways? Many types of plastic will degrade in UV light but this stuff is in the dark and it just falls apart. A mystery...