A Cautionary Tale about Dust Blobs
After just over a year of extremely happy use of this projector, I encountered the dreaded 'waving-dust-blob' issue. I solved that one issue but produced another dust-related issue in the process.
This was the same day as a clean-up of the projector-room; which did yield some dust but shouldn't have affected the ceiling-mounted projector...
As a warning to other users, I'm going to summarize both what I did, indicating with asterisks (*) what you should never do.
(Some of which I did myself.)
Right off the bat I'll say this: whilst DLP projectors normally have a partially-sealed light path (from the color wheel to the main lens); in the case of the W1070, this is only partially true for two reasons:
- The lamp and lamp assembly is ventilated for cooling purposes and for this reason cannot be sealed; so dust is expected to accumulate here. Fortunately, removing the lamp is simple on this projector and cleaning it simple as well.
- However, we'd expect dust-sealing from the color wheel onwards (through to the main output lens) since this is standard for DLP projectors.
Alas, this is not the case with the W1070 - or at least not on my specific unit (a Feb-2013 built, HW Rev 1.03). It appears that there is a deficit of dust-sealing beneath the lens assembly; making it vulnerable to dust accumulation which can produce dust spots that wreck the projected image.
Last night we noticed a 'waving' aberration at the bottom-center of the image. It was very obvious on bright scenes and extremely distracting.
It looked like this (I've highlighted the affected region):
Because it was moving ('waving') constantly, it was extremely noticeable.
This is an issue I've seen reported here before and the reaction is normally to RMA back to BenQ; but I'm a few weeks out of warranty so that's not a real option for me.
Also since it was both moving/waving and gently changing color, I could be pretty certain that it was:
- In the path of airflow; and
- In front of the color wheel (were it behind the color wheel, it probably would've been both static in movement and not changing color)
This narrowed it down to either dust (or the like) around the lamp assembly (in the light-path); or around the opening of the color wheel. Since the lamp assembly is easy to remove and the color wheel is visible when doing so, there should be no warranty issues with giving the assembly a clean.
So that's what I did. Following the manual, I opened up the lamp compartment and removed the lamp assembly:
The assembly looked like this:
The opening of the color wheel looked like this:
..as you can see, the wheel was on the blue segment!
After relatively careful inspection of the lamp assembly, I didn't notice any obvious strings of dust (and the specs of dust on the actual bulb reflector were certainly not the cause of the issue I was seeing). It was evening so I was using artificial light; so it's possible there was more dust than I could clearly see (* BAD IDEA: NEVER ATTEMPT ANY REPAIR/MAINTENANCE WITHOUT PROPER, BRIGHT, SUNLIGHT! *)
Using camera-cleaning-safe, low-velocity canned air (that I had verified - by spraying onto a mirror - left no marks, streaks or liquid!
), I gently - from a distance - sprayed the lamp assembly - whilst it was removed from the projector (* NEVER DO THIS WHILST THE ASSEMBLY IS STILL IN THE PROJECTOR!! *)
; including the bulb itself via the ventilation holes. A bit of dust did emerge; but it didn't appear to be much.
And this is where I went wrong: having seemingly had little luck with cleaning out the removed lamp assembly, I gently blew around the opening of the projector itself with the canned air; in the general direction of the color wheel opening where the lamp would normally sit (* NEVER DO THIS! *)
. A lot of dust emerged; so although the opening appeared to be clean to the naked eye, there was likely dust around this region that was causing the issue. I had thought that provided I ensured that there was no airflow that could cause dust to slip behind the color wheel, I was safe. (* WRONG! The W1070'S LIGHT PATH IS NOT PROPERLY SEALED! *)
After allowing the dust to fall out of the opening and onto the ground (I did this whilst it was upside down), I was satisfied that I'd resolved the issue.
And I was right: placing the assembly back into the projector; closing the cover and powering it up with a bright image displayed, immediately I could see the 'waving' aberration was gone. Score!Until we put on a dark scene: and now I could see dust-spots (shade-above-black circles) throughout the image
. There were half-a-dozen of these or more; and they wrecked any dark scene.
Adjusting the focus of the projector on a black scene (eco-blank), I could bring these into focus: they looked like stars in the night sky. Disaster.
I powered off, waited for the lamp to cool, removed it again, and inspected it: it looked perfect.
I then did the standard 'dust-behind-the-lens' detection test: I shone a flashlight through the color-wheel opening ('simulating' the bulb); and looked through the front lens like a microscope: and lo-and-behold, the same pattern of stars was visible.
Doing so, I also noticed a fortune of light leaking from beneath the lens assembly, indicating the bottom of the assembly is not properly dust-sealed.
This is either a design-flaw (on older models like mine perhaps?) or a manufacturing defect; since the light-path from the color-wheel onwards should be sealed in a DLP projector.
So what had happened? My gentle blowing around the region where the lamp housing sits had successfully removed the dust from in front of the light-path causing the original issue, but re-settled it in the poorly-sealed lens assembly; causing this new issue.
Once again, the dust-behind-the-lens issue is one that I've seen reported on this model several times before (but not recently); so I'm hoping this is an issue that BenQ has addressed in newer hardware revisions of the projector. There's no easy way to correct this either, since the lens-assembly is within the projector itself and not user-accessible - so it needs to be sent in.
The lessons learned are thus:
- If you experience either my original dust-around-the-lamp issue or my later dust-in-the-lens issue, and you're still in warranty, RMA it back to BenQ.
- If you experience my original dust-around-the-lamp issue and are out of warranty, there's little risk in removing the lamp assembly and giving it a clean (whilst it's removed from the projector!); provided you do so in a manner that doesn't produce streaking or leave further dirt.
- Do not assume the light-path from color-wheel to lens is sealed. It isn't. This means that any form of cleaning within the projector itself should be done in a localized manner; and without any methods that might shift dust around in an uncontrolled fashion (meaning compressed air is out of the question).
I've contacted the seller of my projector (I purchased via a reseller) to see if I can arrange a repair: but since I'm just a few weeks out of warranty, I suspect it's going to cost me.
In the meantime, let this be a cautionary tale to all about the perils of dealing with dust within any projector!