Dwin TV4 projector with maybe a bad lamp. But before I buy a new lamp (if I can even find one) I want to make sure this lamp is indeed bad. It looks OK but is reading open with my VOM. Should a good lamp read closed with my meter and if it reads open it must be a bad lamp?

Logically, a light bulb is a resistor, so you should get a reading of x ohms...

I might be wrong, and my theoric technical knowledge is 15 years behind, still in the electronic class room, but I would tend to think that an open reading means a bad lamp.

I'd agree with Cubitus if I knew what technology the lamp is and whether that type of lamp should read open. Now, I KNOW it's not neon, but neon reads open. Incandescents read illogically low resistance because applying voltage to the lamp increases its load resistance! If you have an arc lamp of some type, well, then ? ?? ??

The Dwin manual doesn't say the actual lamp "type", only that is is a 250watt. If I was to guess (it is a bout 6 years old) it is some sort of metal halide, as I think that is what many projector mfgs were using at that time. I know it's not a Xenon

It depends on the design of the bulb. Some will read open and be fine because they are an arc type bulb. As far as Dwin goes I don't know.

What does the projector do when you power it on? Usually, if it doesn't come on there is some type of indicator or code of blinking LEDs if there is a bad bulb.

I own a TV4, I would have bet money a good lamp would read some kind of resistance. I took my lamp out and measured it with a Fluke digital... and NO it does NOT measure any.

It is imposible to tell if a new lamp will get it running again.



I sent you a PM

Knightwing, do you read no resistance, which is zero ohms, being a short circuit; or an infinite resistance, which doesn't give an indication on a meter, is called an open circuit, and might also go by "and NO it does NOT measure any"?

If you read a short, it could be some kind of incandescent lamp. All incandescent filaments increase immensely in resistance when heated. Still, there should be some measurable resistance.

If you read a short, it could mean there's some kind of coil in there, which would look like zero ohms to a DC meter.

If you read an open, it could mean the bulb requires a high voltage to cause an arc or some other condition that then allows current to flow, but the small voltage and current of a meter won't put it in that state.

So we don't know yet.

All the projector lamps I have seen, are driven by a high voltage (2KV or greater) power supply. The reason the power supply is such a high voltage, is because the lamp contains two electrodes, and a metal vapor, which when exposed between the two electrodes, causes a discharge. At low voltages the impedance of the bulb will measure infinite, as no corona/discharge occurs to allow the passage of current. A good analogy is a lightning bolt, a huge voltage needs to develop before the current can flow from one location to another.

These bulbs also work on AC voltage. If they are exposed to any DC component, the material from one electrode plates onto the other, and the bulb fails. Often projectors that are going through bulbs quickly have a problem with incorrect regulation of the voltage, current, or is producing a DC offset in the AC signal to the bulb.

What bcf says about DC is not caused by trying to measure it with a voltmeter -- that's way too little voltage.

On the other hand, I heard a story once about a physics student who checked out a ballistic galvanometer, ran about thirty feet of wire that was bits and pieces of phone wire from the DUT to the meter, and the galvanometer didn't show anything at all. He measured the meter for continuity and found it open.*

So he checked another one out of the stockroom -- same result. The next three were the same. Finally someone in the stockroom asked him what the hell hewas doing. He told them. They freaked.


*the current from a voltmeter when measuring resistance easily blows a galvanometer.

Like in the old days you would not want to loan out your VOM. Some yahoo would put it on ohms and start poking around his car for wiring problems. Then he'd bring it back... "I don't think this thing works.". Of course not, he let the smoke out of it.

TGFDVMs.

Thanks to all for some good suggestions. I have sent the cage for relamping. A few sources were able to offer a re lamp.

One of the folks I talked to validated what some of you have said - that this lamp would show open regardless of condition. So I have no way to know if the lamp is good or bad.

No way to know until I install the relamped back into the PJ.

The LED sequence on the DWIN PJ indicated nothing is wrong (according to the DWIN manual, there is a flashing sequence for a bad lamp and it was not not blinking in that manner).

Customer realizes it is a gamble to try before consigning to replace the PJ.

I've sold many TV3 but looking at my records, only 2 TV4 PJs. The other one I sold seems to still be working.

Wow, Ernie it must be tough being you. That said... You are correct once again!

The lamp reads as open.

The pm I sent him which included the name of the distributor, the phone number, the part number, and the approximate price probably has some punctuation problems as well. I am sad that you ( Ernie ) are not able to pick that appart as well. While I admit you are correct, I think it would be a stretch to misinterpret what I said, or at least tried to say.