Low voltage lighting transformers


One of my hanging ceiling lights has decided not to work any more. It's a low voltage halogen with a small built in transformer, an LET 60 type 60-watt 12 volt unit. It looks like the transformer is gone; it shows almost no voltage at the output with a DVM. I get about 1/4 volt that rapidly dwindles to 0.
My question is whether these transformers *need* some load to actually product voltage, in which case my DVM is giving me a false negative. This is much like the "floating 85V" you often get on a switched off 120V line when using a high impedance DVM to check it.
Before I drop $20 on a new transformer, I'd like to make sure it's really the culprit. The lighting store I bought the lamp from does say that they "do fail in service sometimes"..... hardly real evidence.
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Andrew Duane writes:

Transformers don't. Assuming it really is just a transformer, not a charge pump. Why not swap one of the others in to test?
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Well, it's a little sealed box, not necessarily a "transformer" in the traditional sense. It could well be some funky switching supply; it's all sealed up in a black epoxy cube. And I have no others to swap with; this is the only fixture of the type I have at the house.

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Ok so you take and make sure the bulb is sound using the R scale on your meter, and you verify that input power is available on one of the ACV scales, what does that leave? Am I missing something here?
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On 10 Apr 2007 06:56:13 -0700, "Andrew Duane"

Almost every test has a matching test. Here it is to measure the resistance of the rest of the fixture. If it's not infinite, the lights are probably good.
Do you have a backup burglar alarm battery that you could est those lights with. Most of them are 12 volts. Or a couple 6 volt lantern cells connected together. Or even the car battery-- you could bring it in, or if the fixture is off, you could take it out to the car.
In most lightbulbs connection direction doesn't matter, not sure about these.
If you put the battery on a table, you can take 6 or 8 feet of lamp cord and put alligator clips on each end, connect two to the battery and two to the lights. I even have insulation piercing alligator clips for places where there is no copper showing, but I had to buy a box of 10.
Another thing you can do is put a hat pin or a corsage pin into the wire and attach the alligator clip to that.

20 dollars doesn't seem like much in this situation. The alternative is to do the tests above. and if there is more than one bulb, it's unlikely they all failed at once or that the wires going to each one all failed at once.

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It's probably an electronic low voltage transformer. Some types can't be measured with a standard DVM. Make sure your lamp is good and check input and output connections. From my experience with halogen lamps, most often the sockets self-destruct from the excessive heat

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