Your indication regarding the 100% does not necessarily indicate a damaged chip (sensor). Many chips do not work by actually sensing the toner but by usage or other tricks. We cannot be sure about what happened but replacing the drum and affected items should solve the problem. Needed parts may be found at
You need to do s head clean.
This could take 2 or 3 goes but should fix it you will find head clean in the maintenance settings.
It eats the ink so only do as you need.
let me know how it goes.
If you printer has an additional memory card fitted then remove it (powered off of course) and turn on and see what happens. If the fatal error is still there then with the age of the machine (getting on in years) it is better to replace it as the error refers to the cpu in the control board and that's expensive on older machines to replace.
the best soloution is to replace the unit with a brand new one as reset fuses are difficult to work with on fuser units but if you search the internet you might be able to find a reset kit from alibaba or amazon