A few months ago, I bought an InFocus video projector on eBay, still hoping to watch movies on the wall of the family room. It’s about 1/12 the size of the behemoth Sony projector I was trying to repair earlier, and quite a bit sharper and brighter; so if I can get it going, it’ll be a nice replacement.
When I received it, I immediately noted two problems: It shuts itself off after anywhere from seconds to hours; and it has a yellow silhouette running up the middle of the picture, kind of like the face/vase illusion.
I’ve taken some time this afternoon to disassemble and diagnose the projector; so although it’s not fixed yet, here’s what I know so far.
Chasing the Yellow Blob
In which Keith removes Crusty Gummy and washes a filter carrier
From the looks of it, I was pretty sure that the blob was going to be something wrong with, or wrong on the surface of, one of the lenses, mirrors, or filters. Yes, it looked a little like an LCD ruined by being left in a freezing car overnight, but not quite. So I dug in to follow the light path through the projector and see if it would be apparent what was wrong.
After popping the cover and removing the main circuit board, I could see most of the periscope-like light enclosure. I removed a couple of lenses that dropped in from above, which were clean, and looked at a couple of mirrors, which were also clean. The next thing I wanted to check was the LCDs.
In order to get to them, I had to take off the collar above/around them, remove the two cooling fan / speaker assemblies, and remove the main lens. The LCDs were mounted to the lens carrier and looked fine; their removal left access to this cavity where the RGB light paths converge.
I didn’t notice it until later, but someone had already been here before. Loctite on the RG screw tabs and missing from the B tab.
From a different angle, the problem was obvious.
The filter between the blue light path and the blue LCD is all melty. Bad.
First things first. I gently peeled off the Bad, scrubbed all the goo off the glass carrier with Goo Gone, washed all the Goo Gone off with Dawn, rinsed the Dawn off with water, and dried the water off with a paper towel. (Life is sooooo complicated.)
Here it is all shiny and ready for . . . whatever comes next.
While I was in there, I detached and examined the other two filters. They didn’t look colored, just a light neutral grey in a very familiar sort of way. Apparently the filter isn’t what makes the blue blue (that’s the blue half-mirror further upstream), so maybe I can just put it back together and see what happens.
Reinstalling the Filter Carrier
Assembly is the reverse of disassembly.
The projector is back together and emitting blue light when it should be emitting black. The Bad was the polarizing filter that makes the LCD do its thing, so I’m going to have to find another one and put it back. It’s still emitting shades of blue; it just puts out quite a bit of blue when it should be going all the way to black.
I’d welcome donation of a spare polarizing filter from a differently-ruined LP290, and I’m shopping for a broken one. But partly for sheer “I can’t believe you did that and I can’t believe you got it to work” value, I’m sorely tempted to get a polarizing filter somewhere else and see whether it’ll do the job. Like a photographic filter. Or an LCD from dead equipment. Or sunglasses.
Of course, none of those are good ideas. It obviously gets hot inside the projector, and meltage problems are going to avalanche as the filter warps and discolors and becomes less transparent and absorbs more energy from the light and heats up and warps and discolors. So I’ll at least look around for a spare projector to cannibalize.
The projector has the lamp cover interlock switch and AC-DC power supply on the starboard side and the DC-DC power supply and lamp ballast on the port side. The AC-DC supply is always on, and the DC-DC supply appears to be under control of the microprocessor that runs the soft power button and monitors the sensors scattered throughout the projector.
The AC-DC power supply checks out okay, as far as I can tell. All of the electrolytics test good with my Capacitor Wizard, and the three voltages (16.5V, 6.6V, and 3.3V) are present on the edge connector that plugs into the main board.
I took the projector parts over to Ron Tozier, and he suggested testing all the voltages with the projector in standby, with the projector on, and after the projector shuts itself off. That should help determine whether the failure is in the AC-DC power supply board (probably not), in the DC-DC board, or quite possibly with one of the sensors. He also noticed that the main board has nicely labelled test points for lots of voltages, including not only the raw AC-DC supply outputs but also regulated and switched voltages under microprocessor control.
I printed out a digital pic of the main board, highlighted all the power supply test points and wrote the standby and on voltages next to them, and am now waiting for the projector to shut itself off. Of course it would pick now to stay on for hours.
I do note that every time I turn it on, as it powers up the lamp, I hear a chittering sound like an ultra-high-pitched buzzing. I think it’s the ballast going out, and I’m pretty sure the projector would sense a ballast failure and shut itself down. So I suspect I have a pretty good idea what I’m going to find is causing that problem as well.