Chainsaws

Ronald,

The "little gray switch" is the lock and unlock so you can remove the top cover to access the air filter.

As far as removing the chain cover, loosen the tension screw on the chain tension, just a little maybe a quarter turn CCW, the chain may not really loosen with the cover in place. Next make sure the Brake handle is pulled back, you should feel the brake dis-engage, then remove the bar bolt  (Nut) and the cover should come off.

However If the Brake cover does not come off then there may be a component of the band brake which has failed or broken, In which case, As a last resort,  you will need to carefully pry the cover off, I suggest possibly a wooden block be used as a prying surface, and Not prying directly on the plastic cover or parts, prying at the top, and then at the botton around the area of the brake band. You only need to move the cover about 3/8 inch top and bottom and the brake cover should come off. But the more difficult part will be to determine exactly what went wrong with the brake band, and you may need to buy parts to re-build the brake cover, and then test that brake is working as designed after the re-build, or buy a complete brake cover which brand new is a little pricey, 

I hope this helps and If I can be of further assistance, Please let me know.

Karla

PS. I am Not a Husqvarna Representative or a Repair Service, Just an experimental chainsaw person.