One other possibility, Did you check the color wheel sensor. On a HD20 I would see something like this when it needed cleaning. Never saw much for dirt but a good dusting of the sensor with a small soft brush and clean air would solve it for months of watching.
Vizio P75-C1 | OPPO UDP-203 | Samsung UBD-K8500
Denon AVR-x5200w | Nvidia Shield Android TV | C =Axiom VP150 |FL/FR =Axiom M60 |SL/SR =Axiom QS4 |TFL/TFR =Bose 161 | TRL/TRR =Bose 161 |Sub =Reaction Audio S-15 500W SEALED SUBWOOFER