My Optoma EP739 started exhibiting color-banding and strong color shift after years of great service. After trying other suggestions that didn't work, here is the FIX for my unit. I have not seen this posted anywhere else.

Problem: After 10-20 minutes of use, color-banding and then a strong shift to purple/green with almost no red. If the unit is turned off for 5-10 minutes to cool and then powered-up again the problem goes away, only to come back in another 10-20 minutes. Enabling the "High Altitude" setting in the Setup Menu helped for a while (a week or two) since it forces the main cooling fan run at high speed always, but then the problem re-appeared.
Reason: Overheating. The electronics are overheating. Like several people have suggested: First step: Open the unit up and blow-out/vacuum all of the accumulated dust. Assure BOTH fans (there is a small drum blower directly cooling the lamp and a larger regular fan that circulates air through the entire unit) are operating and clear of debris.

Once you have done that, then look for the REAL issue. With the front panel (i.e.the panel with the hole for the lens) removed and looking into the projector from the front examine the metal heat shield on the right side above the lamp. In my unit, because of years of service and heat, the aluminum lamp housing had deformed slightly, tilting this sheet metal heat shield directly INTO the air stream from the fan. This restricts the airflow enough to reduce cooling capacity. This metal shield should be high enough above the lamp to be TOUCHING the plastic case. If it is bent down and is halfway into the air stream then it restricting the exhaust airflow, causing the overheating.

Fix: Bend the heat shield back up so that it is not in the exhaust airflow. It must be ABOVE the airflow, protecting the plastic case from the heat of the lamp. This simple remedy fixed the issue for me. My projector has been running 2-3 hours a day for 10 days now with no banding issues at all. That's it. Simple fix.

Hi, genelewis! Well good news for me, and also hope for you; I got my projector to work correctly again, at least it has not had the problem for a couple of days of probably 10 to 12 hrs use of movie watching, before it could not go an 1hr without the purple issue.

I was looking at other sites and this one with other projectors and it sounded like just dust in the projector... after just about 3 years now without a cleaning I think it needed some maintenance, so I carefully took the bulb out (1 black screw on the bottom) and opened the projector (7 metal screws in total), and after some investigating on any wiring that may interfere (only on the inside back of the white top cover, were the inputs are: a wire band and some small metal sheets that kind of grab the top) I pop the top, not that hard.

After that I just carefully used a can of compressed air to blow away from the projector any dust I could reach and in some of the crevices I saw, being careful were the mirror is (were the bulb was); I was tempted to get the glass that covers it off to get some dust off but the screws are small and kind of hard to get out, so I left that alone. Cleaned any dust accumulated on the air intakes with a clean soft cloth and closed it up again. I did not want to touch anything else unless this did not work, but this did the trick! I'm happy with my H31 once more.

I hope this helps you, good luck. Let me know if you need some more details