Low voltage recessed light diagnose testing

[echo_jey]

I'm trying to pin point the cause of one of the low voltage recessed light is not working. so far I have done the following,
Continuity test passed on both working fixture and not working fixture
Voltage test while switched 'ON' - working fixture reads 14.5 AC Voltage, not working fixture reads 13.8 AC Voltage
I could not do Amp test on both fixtures.

Bulb is fine on both fixtures - MR16, 12V, 50W
Bulb base - GU5.3, continuity test passed on bulb base.

If the transformer is culprit then how can I get 13.8 AC V reading ?
Could someone please explain clearly?

[papo]

Hello

I'm not familiar with the type of lights you are describing, so this is guesswork. The transformer you mentioned, is this an old-school, "real" transformer or more of a switch mode thing? The latter are sometimes labeled "electronic transformers", and while they usually contain transformers, they might be switch mode converters of some topology.

If this is the case, that switcher might be dying and look OK when no load is attached, but as soon as you start to draw current (i.e. by mounting the bulb), they creep out. Usually bad capacitors are the cause of this failure mode. Was the 13.8 V reading measured with or without bulb in place?

Regards
Matt

[echo_jey]

Thanks for the reply, I couldn't see what type of transformer is used since the fixture is mounted on celing and I'm only see the can with two wires.
I measured the voltage with bulb and without bulb, both reads out 13.8V

[SeanB]

Change the lamp base, as they often will go high resistance on the inside where the lamp pins connect. Cheap enough to do, and check the connections at the other end of the 2 silicone wires are making good contact in the screw block, and the wiring from the transformer is connected firmly there at the lamp side. Try the lamp direct on the cables as well, if it does not light then the fault is upstream, but most of the time I find the socket or the connector there is either arcing and intermittent or burnt open

[echo_jey]

I have tried the bulb without GU5.3 base and still no light,  this eliminate the doubt of socket base.

[London Lad]

Is that joint just twisted together? If so re strip it and used a good terminal block, its got to carry over 4 amps.

Silly question but have you tried a substitute lamp?

[echo_jey]

Yes it has protector but I removed to test with multimeter, I tried with working bulb and still no light.

[London Lad]

I'd still be inclined to strip and re make them but its hard to see from the photo

[SeanB]

Time to pull the can out then and see the burn on the inside wiring. It can arc and go high resistance, or the local transformer connection is doing the same. If it is an electronic transformer change it, they are cheap and nasty. I saw them today for $3 each retail.

[echo_jey]

but continuity test proved no connection issue? , I did continuity test on socket pin holes and then removed the socket and tested continuity on just two wires coming out of can, both time continuity test passed. so can I eliminate anything related to connection issue?

I'm hesitant to pull out the can from ceiling since its in-laws house and I don't want to mess up things without pinpoint the issue.

[London Lad]

Sorry how are you measuring continuity if you cant get at the transformer? Continuity from where to were?

[echo_jey]

oh ,  so both side of transformer is not connected regardless of what type of transformer is used?  like this  " ] Magnet [ "
I'm new to this electrical and electronics, I recently bought Milwaukee 2017 TRMS Multimeter and wanted to take advantage by solving this existing problem.

if I get Voltage reading on two points then should I get current flow when load attached?

[London Lad]

The problem is that you may see 12 volts with your meter but it doesn't draw any load (or almost none anyway) whereas the lamp will draw 4 amps plus.

If you have a poor joint or burnt joint it may pass 12 volts ok with no load but that voltage could drop away once you connect the bulb.

A faulty electronic transformer can do the same thing, show 12 volts with no load but fall away to nothing under load, but this is less likely to happen.

When you measure continuity across the output exactly what resistance are you reading?

[echo_jey]

I measured continuity using MM setting and heard beeps. Didn't measure resistance.

[London Lad]

OK as a start separate those twisted joints and try a known good lamp straight across there.

Has your meter got a LoZ range ?

[han]

test in loZ mode , put a 1K resistor parallel in the DMM.

[echo_jey]

Yes it does Lo-z , please see the manufacturer link http://www.milwaukeetool.com/instruments/digital-multimeters/2217-20nst
I tried with alligator clips to connect those two wire ends with good working MR16  bulb pins but didn't light.

[London Lad]

OK you either have a bad joint between those ends and the transformer or a faulty transformer.

While you are at it try measuring the output at the wire ends with your meter set to LoZ

[echo_jey]

"OK you either have a bad joint between those ends and the transformer "

But I did continuity test and passed on those two end of wire with DMM, still possible those two wires suffer from bad joint?

When I did continuity test on those two wire ends, is it on Secondary circuit of transformer? Please see the link for picture
http://farside.ph.utexas.edu/teaching/302l/lectures/img1136.png

You think bad join in primary circuit?

[kolbep]

Heres my thoughts.
Arè you sure that the non-working fittingis giving 13.8v out at the bulb connector.
As you are using a new meter, you might be reading 138mV,  or 1.38v. Either one means that there is a fault between the supply, transformer and the connector.

If you are getting definate 12 to 14 volts, then try this
your meter probes might be thicker than the bulb pins, in which case sticking them into the connector can make a good connection even if the bulb doesnt.
try swapping the holder and bulb from the working fitting onto this one. You will then be able to elimate the holder, bulb or transformer as the problem.

[echo_jey]

When I read at the end of wires got 13.8 ACV
when I read at the socket pin holes got 13.8 ACV

I already tried with different working bulb, but I don't have extra socket , since working fixture has socket which has no joints, directly coming from can.

[London Lad]

"OK you either have a bad joint between those ends and the transformer "

But I did continuity test and passed on those two end of wire with DMM, still possible those two wires suffer from bad joint?

When I did continuity test on those two wire ends, is it on Secondary circuit of transformer? Please see the link for picture
http://farside.ph.utexas.edu/teaching/302l/lectures/img1136.png

You think bad join in primary circuit?

As I understand it you can not see the transformer and do not know if its electronic or just a simple one as per your diagram.

A 'continuity check' does not prove the connections can carry current. If you are reading voltage but there is no current available to light the lamp under load you need to look for poor joints or failing electronic transformers.

Forget the theory for a while and use your eyes. Check the joints and cables from the transformer output right through to the lamp. Don't meter them any more, take them apart, re strip the wires and re make them.

[echo_jey]

sure I'm going to take out the can and check the joints and visual inspection,