I was cleaning the contacts of the buttons . . .

on the underside of circuit board on the 3000 with isopropyl alcohol (they were playing up) and noticed that I had removed some of the thin film that coats the circuit board . Does anyone know how important this is and what it does? Thanks

just the film or the connection itself? And are you sure the film wasnt just gunk that accumulates over the years?

Yeah just the film. Yeah I did think it might be dirt etc but I am pretty sure the film is a coating of something?

I am thinking it might be a conformal coating.

"Background on Conformal Coatings

Conformal coatings are applied to Printed Circuit Boards to protect the mounted electronic components from contaminates such as dust, sand, moisture, salt mist and conductive particles. They provide environmental and mechanical protection to significantly extend the life of the components and circuitry. Typically only a few mils thick, conformal coatings also provide resistance to several stresses including abrasion, shock, temperature, ozone and ultraviolet degradation. They enhance performance and allow greater component density due to increased dielectric strength between conductors.

Conformal coatings used on printed circuit boards are typically acrylic or silicone, but may also include epoxy, urethane, parxylene (parylene), and UV-curable coatings. They are traditionally applied by dipping, spraying or simple flow coating, and increasingly by select coating or robotic dispensing."

Does anyone have any advice on whether I should re-apply this coating or not? Thanks

You don't want parts on your circuit board to corrode after time. Use some clear finger nail polish to cover it up.