I’ve redone the grille cloth on my U890’s. Aside from the panel being cumbersome to handle when removing it from the frame, the job is pretty easy. On the bottom of my panels there is a piece of 1/8” Kydex plastic that is attached with screws to the panel bottom and needs to be removed. Take note of how the 3 stator/membrane wires are routed through the grille cloth.
Once the panel is removed, it’s just a matter of removing a myriad of staples from the bottom and sides of the panel to release the grille cloth. There is no sewing involved, only stapling.
I first attached the new grille-cloth to the bottom of the panel at about the midpoint, the material then goes up the backside of the panel and stapled along the angled side of the panel frame, wrapped with over the top of the frame, down the front side and again stapled to the angled side, wrapped over the bottom front edge and stapled to the bottom.
You’ll need to keep the material taut, but not too taut, as your stapling to avoid wrinkles.
Depending on the vintage of your panel the top may also have a Kydex cover that will need to be removed.
My earlier U790’s had a top cover while my newer U890’s don’t.
Anyhow, good luck with your project, I hope the above description made sense. If others in the group can add to this, or describe the procedure better, please feel free to do so.
John