Replace any module that the green status LED does not illuminate when the power cord is plugged directly into the back of the module.
Personally, if money were no object, I'd suggest a system upgrade to a Partner ACS R7 to bring the telephone system up to date.
Short of that, you can find repaired/refurb 206 modules for sale from many reputable online dealers. If the existing configuration suits your needs, you could simply use the existing processor and replace the defective 206 modules.