Anyone with experience on Dell DLP projectors?

[N2IXK]

Just inherited a Dell 1200MP DLP video projector that needs repair. The unit will start up normally, go through the lamp warmup, and then run normally for about 30 seconds. At this point it will either:

A: Go to monochrome, start making a faint whining/whirring noise like a fan or motor running, and lock up (image freezes, no response to remote or buttons, except for power off)

or:

B: Simply shut down the lamp, go through the cooldown cycle, then go to sleep.

I have already tried:

2 different replacement lamps (yes, the lamp timer was reset).

Cleaning the dust out of fans and filters. All fans appear to be running OK.

General internal inspection for loose connections, bulged electrolytics, etc. (nothing obvious found).

Resetting to factory default settings through the menu.

This might make a nice unit for home use, and I would like to get it up and running if at all possible. It would seem that all the "big buck" parts like the DLP chip, lamp, and optics are OK, since it does function properly for a short time. I haven't been able to find a schematic anywhere yet.

Anybody out there have any experience with these units? Any "common failures" to be on the lookout for?

[crtfool]

Most likely the Color Wheel has failed - very common failure on DLP units.

[N2IXK]

Up until the unit suddenly shuts down or locks up, the colors are displaying properly.

I would think that if the color wheel was not working that I would be seeing wrong colors, stuck on red/green/blue, etc. Is shutdown/lockup a characteristic symptom of a failed colorwheel?

Assuming the colorwheel could cause this, is there any way to test besides substitution? The part is going to cost between $75 and $100, so just throwing one at it on a guess seems risky. I assume it is on some kind of servomotor, and produces a sync pulse to feed back into the electronics somehow?

[crtfool]

Originally Posted by N2IXK

A: Go to monochrome, start making a faint whining/whirring noise like a fan or motor running, and lock up (image freezes, no response to remote or buttons, except for power off)

This is what makes me think that it is the Color Wheel failure.

[CoogarXR]

The whirring noise is probably the bearing in the color wheel. I know some samsung DLP TVs have a brain fart when the color wheel RPMs dip below a certain rate.

[Eric H]

Perhaps you can lube the motor (WD-40 or Zoom Spout) and get it running long enough to determine that it is the problem?

[N2IXK]

I had put the thing back together and put it up on the shelf. Will have to open it up again soon and look into the color wheel.

What is the actual failure mode on these things? Mechanical, like bearings drying out and dragging? Why would the unit always lock up into B&W mode, rather than red, green, or blue? According to the pictures I have seen of the wheel for this unit, there are 4 filter segments, R, G, B and clear. If the wheel stopped rotating randomly (as from a bad bearing), wouldn't there only be a 25% chance of landing on the clear segment each time?

[crtfool]

From an eHow tech article:

"The most common sign that the color wheel is beginning to go bad is a high-pitched hum that it tends to give off. This hum can be noticeable as long as six months before the wheel goes out and is caused by the bearings starting to fail within the color wheel. Eventually, the image on the screen will freeze and lose color."

Read more: Troubleshooting Problems on Samsung DLP Projection Televisions | eHow.com http://www.ehow.com/way_5200618_trou...#ixzz26y8zsYKI

[mstaton]

Can be bearings/motor or the wheel glass is broken.

[Eric H]

Isn't it possible to run it with the cover removed and see if the wheel is turning?
Interesting that the CBS System (more or less) did find a home many decades after it died.

[N2IXK]

The way this thing is built, the whole optical system is covered by the main board, and the various cables are too short to allow it to be powered up with the board hinged up out of the way to allow access. Real PITA design from a service standpoint.

Didn't see exactly where the colorwheel assembly was when I had it apart, so I don't know if you can see any part of it spinning while installed.

[mstaton]

If you pull the lamp out, you may see it through the light tunnel.

[N2IXK]

After a bit of testing, I think I have found the problem with the unit. It isn't the color wheel itself, but the optical sensor that measures the color wheel speed/position.

I took the entire color wheel unit out of the optical assembly and checked for obvious issues like tight bearings, etc. Finding nothing, I plugged everything back in. The projector would then operate normally, but (obviously) gave a monochrome picture. I used a scope to look at the signal from the color wheel sensor, and it looked reasonable (narrow positive going pulse of ~ 3Vpp at a frequency dependent on wheel speed). Feeding a standard NTSC video signal into the unit produced a 120Hz signal (2x the frame rate), just as I was expecting.

Finding nothing obviously wrong, I reinstalled the color wheel and immediately the unit was back to the old lockup and shutdown routine. I hooked the scope up to watch the wheel speed signal during the failure, and the amplitude of the pulse SLOWLY fell to ~2Vpp or so, when the wheel speed suddenly shot up (presumably as the wheel speed servo went out of lock), then the unit went into shutdown. Hmmm....

I disconnected the wheel speed sensor, and injected a substitute pulse from a function generator. As expected, the projector functioned, but with wild variations in the colors because the wheel was no longer synchronized to the video signal.

Armed with this information, I concluded that the optical sensor was dropping it's output level as the wheel assembly was heating up from the lamp right next to it. I pulled the wheel assembly out again, hooked everything back up, and tried heating the wheel speed sensor with a heat gun while the unit ran. The pulse amplitude dropped below the critical level, and the unit shut down.

So now I need to find a replacement for the little optical sensor. It is mounted on a tiny PCB, with a couple surface mount resistors and caps. It is a tiny 4-legged SMT device, presumably an infrared LED and a phototransistor in one package, which bounces light off the hub of the color wheel, and looks for the little black timing mark on the hub. No visible numbers or manufacturer logo on it, unless it is on the bottom side (will desolder it and check). May be time to start digging through catalogs and datasheets to find something similar. I have my doubts that calling Dell will produce any positive results, as they likely only sell the entire color wheel assembly as a unit at an obscene price.

UPDATE: After a bit of digging, I have identified the sensor as a Sharp GP2S27 series photointerrupter. The part was discontinued as of last year (and the suggested replacement is functional replacement only--different package), but DigiKey still has a few GP2S27s in stock. A few are on the way at < $2 each, with shipping costs to exceed the cost of the parts themselves...

[N2IXK]

Part arrived today, and the unit is fixed.

Wheel speed pulse good and strong (nearly 4Vpp with new sensor), and amplitude stays up when everything heats up.

Filed the extra speed sensor away with the spare lamps I got with it, and should be good to go for a good long while. Thanks all for the input!

[crtfool]

Good job in isolating the faulty sub-component on the Color Wheel, and repairing it.