52" rca model #p52930bl

The plastic screen itself never gets dirty on the inside, unless a spider has taken up residence nearby. What you are likely experiencing is dust built up on the CRT lens and mirror - which would cause the picture to look dull with low contrast and brightness. If that is the case, you may find on your model that the screen either pulls out or that there is a wood piece at the bottom that is hiding some screws or maybe the speaker grill needs to be removed to expose said screws. Be gentle cleaning the mirror, as it is surface coated and could be scratched easily.