A colleague has asked me to look at an intermittent fault on his BenQ video projector. This is the first projector I've worked on, I'm more used to TV and VCR repair (and digital asic design, my "day job").
There seem to be two (possibly related) problems, which both its owner and I have witnessed:1) Sometimes it shuts down during use. Lamp goes out. The red LAMP error led comes on (and stays on), the power led blinks green for 2 mins (the normal power down delay, with fans running) then the fans stop and the power led goes yellow (normal for standby). TEMP led stays off LAMP led stays on. If one then presses the power button the LAMP led goes out and it powers up again normally. It may work normally after this (for hours), or it may shut down again after ten more minutes or so, and one has to repeat the process.
2) The colours can get confused. The one occasion that it's done this while I've had it, the colours just seemed to go funny in the middle of a film. Generally looked like a loss of saturation, and an odd purple hue. A slight flicker of the image too, I think. I powered it down and up again and all was normal again. I guess the colour wheel got out of sync somehow?
It'll work fine for several days between failures.
The owner has had it from new, the lamp is original and has only clocked up 236 hours (of 2000 hour quoted lamp life). So I'm reluctant to think it's a real lamp problem - and a new lamp is rather expensive to buy just to try.
I've taken it apart, checked easy things (PSU, electrolytic cap ESRs, examined closely for bad joints, reseated connectors etc) but found nothing. After putting it back together, I though it might be fixed, but a week or so later it was back to its old tricks. :-(
Anyone out there with more experience of DLP projectors? I see several "user reviews" of this model on websites, many complaining of similar unreliability (but all praising it for good image quality when it works!) Is there a generic issue with this model, or maybe a known fix to apply? I notice several places where there have been EC's applied to the boards (resistors, capacitors hung off at funny angles) suggesting an early model or flakey design to me.
I trawled the web for service info, but found only one BenQ manual (on eserviceinfo, a much earlier PB6100 model), and found no sites offering any BenQ service manuals for sale. Are they generally available at all?
Can one hook a PC up to it, and get an error log out of it or otherwise put it into a "service mode"?
It uses a EUC 250 P/01 lamp ballast, with a small (5-pin?) control cable. It would be helpful to know the pinout of this, I imagine it has a lamp fault line on it. Anyone know? It also says "9137 001 71805 MADE IN HOLLAND" on it, which makes me wonder if Philips were involved in the ballast. Any info here would be gratefully received, I could hang a logic analyser on it if I knew what to look for. One of the signals here has a 2K resistor soldered onto it. An attempted fix for a ballast interface problem maybe? The ballast is pretty complex - with two daughter boards soldered into a main board - and whilst I'm quite willing to reverse engineer things in general, I think this would be quite a hard one as it's multilayer PCBs. So that's a last resort.
Thanks for your help.