How to fix a projector light tunnel
I originally posted this on my old blog but I think it deserves a place here. Whilst it's not an exact "how to" fix a projector light tunnel, it should offer enough information to diagnose light tunnel problems and hopefully, encourage you to fix it yourself. Normally when a light tunnel collapses the user is told to send the projector back and the whole light engine is replaced. This can be costly so if like me, you've nothing to loose and no money to spend getting it fixed in the first place what's a few quid on some glue and a bit of time?
Okay, major panic over - I've fixed my light tunnel! For those who know, I don't have a television and enjoy watching the movies on the big screen with my projector. It's the only way to check out Anelina Jolie's fine form I tell ya! Anyway, about six months ago I had a new projector lamp fitted at Infocus - all very well even though they charged me an arm and a leg. I'd sent it back because I wasn't convinced it was the bulb having hardly done any hours. Anyway, it was and I got the unit back - complete with dust globes on the image and all (yeah nice! they weren't there before!)
Last Saturday I turned on the projector as we were about to watch a film and noticed this shadow across the left hand side. Couldn't figure out what it was and didn't watch the film. I did some research on the Internet (oh where would we be without Google?) and discovered there is a common fault with some projectors. Inside there is something called a Light Tunnel (also known as a wave guide, light tube etc.). It's purpose is to guide the light from the lamp (once it has passed through the colour wheel) through the optics and onto the DMD (the fancy mirror array that does all the imagery). Anyway, this light tunnel is basically four slithers of mirror arranged in a box shape... HELD TOGETHER BY GLUE!!!!
Yeah, really smart isn't it? Stick some mirror together with glue in an environment that is hot. Apparently the glue becomes brittle and fails, resulting in light tunnel collapse where by one or more mirrors fall down into the path of the light. As I said, Infocus apparently just replace the light engine rather than fixing the light tunnel. And they charge a few hundred quid to do it.
Sod that I thought. I'm poor, I'll get one and replace it. No luck though. You just can't buy a light tunnel, at least not one for an Infocus projector off the shelf. Maybe in some dark and dingy corner of the net there's a shady Bob with a rack full of light tunnels waiting for a stream of pissed of movie buffs. Who knows?
I decided therefore to repair myself. I didn't hold out much hope of success because the parts are extremely small, my eyesight ain't the best and to be honest I'd seen reports on the net of people attempting this and failing completely.
To cut a story short and get to the point. It took a couple of days of very careful work, patience and an expensive tube of glue (five quid!) to repair my light tunnel. It's not an amazingly beautiful repair, but the edges are straight to within 0.25 of a millimetre I reckon and here's the best bit... When I fired up the projector to test it - knock me down with a feather because it actually worked! I'm waiting to see if the glue holds - it should do, because its slightly supple and rated from -30 to 130 degrees. In the mean time I will keep searching for broken projectors and light tunnels (hey... there's light at the end of the tunnel you know). Not sure if I managed to eliminate the dust or introduce more into the optics. I'll see that when its a bit darker too so fingers crossed.
As they say.. Time to break out the popcorn!
Here's some photos I took as I extracted the light tunnel.
An update on this
The light tunnel repair above failed within a few months - mainly because the glue was absolutely rubbish despite the price. So, I repaired it again, this time with some regular arldite epoxy resin from the pound shop. Well that was over two years ago and it's still going strong. One other thing I'd say about repairing light tunnels is, keep the area and the mirrors very clean, use some bluetac or something to steady the mirrors when gluing them and do it in stages so it's aligned properly. A decent magnifying glass and good lighting comes in useful too!
Good luck with your repairs!