Digital projectors are funny beasts. They get a video signal from a computer or other device, and display it on a small LCD screen behind the lens. The screen is illuminated by a ferocious gas bulb, xenon, I think, which projects the image on a screen. In operation, they get hot and always have cooling fans, air filters that need to be cleaned, etc.
We had one in a classroom that kept dropping the image to garish colors and static. It was an intermittent problem, the hardest to diagnose, but we had it nailed down to the projector itself and not anywhere on the signal path. I took the projector down off the ceiling and ran it on my desk, reproducing the problem about 1 cycle out of 10. Sanyo issued an RMA (Returned Materials Authorization) and I shipped it to them for warranty repair.
Three days later they called back, leaving a message on my desk phone. They “ran it for two days” and “couldn’t find any problem” but it “needed to be cleaned” for which they wanted to charge us. (“cleaning” consists of blowing out the projector with compressed air, by the way)
The “we plugged it in and the problem didn’t happen” school of diagnostics only pisses me off. Obviously they didn’t cycle it enough times to reproduce the problem. Admittedly it can be time-consuming, and diagnostics can be difficult. I used to inspect circuit boards with a magnifying glass to find evidence of component heating, or gently touch IC chips with my fingertips while the board was live (got a few blisters that way over the years but a really hot chip without a heat sink is indicative). Sometimes I’d cool components with compressed air (in the old days, we used freon) to spot thermal intermittent faults. I’d look for wobbly fans, clogged air filters, pinched wires, delaminated circuit traces, leaky caps, or cracked solder joints. Seldom had to go as far as signal-tracing. Finding the problem does take time.
Disgusted, I didn’t return the call right away. I waited two days and called back. Much shuffling of papers and querying of co-workers ensued.
“Oh, they tested it for two more days, and the picture went all green and full of static. They traced it down to a faulty IC. We’ve repaired it and cleaned it under warranty, and it’s on its way.”
Yeah!
Sometimes no response is the best response!