Did Light Bulb Fail Or Connection Within Desk Lamp Itself? - Page 1
Forum section: electronics / general

author: Boris_yo
author_rank: Frequent Contributor
timestamp: December 15, 2012, 12:15:57 pm
content: I have this desk lamp for more than 5 years now and never replaced its bulb. Recently I noticed it started blinking, especially when I touched desk lamp or just moved it. The bulb is of type that I have never seen which can be observed on pictures below this post. It does not have that much delicate small spring which gets torn in regular incandescent bulb but instead it has similar spring but which is very sturdy looking one and resembles regular spring. The second below picture is the head of desk lamp itself where bulb supposed to connected.I have carried continuity test with multimeter from each of plug pins to the desk lamp head's contact which did not work because I pretty much don't know electricityI tried then resistance test and numbers started jumping around so in my opinion plug conductssomethingto desk lamp's head. Finally I tried cheap china-made voltage tester and it worked. When I moved tester near desk lamp's head and pushed switch, the tester turned on and turned off after I switched off desk lamp. So definitely there is conduction and I think the problem is with bulb but correct me if I am wrong. I would also like to know the name of such rare bulb. Thanks.

author: PeterG
author_rank: Frequent Contributor
timestamp: December 15, 2012, 12:34:52 pm
content: I have a similar lamp and use the following bulbs in it. Never had a problem.http://dx.com/p/halogen-light-bulb-12v-20w-white-4391Regards

author: SeanB
author_rank: Super Contributor
timestamp: December 15, 2012, 12:44:37 pm
content: 12V 35W halogen lamp in a GU5.3 base. There will be either an electronic ballast or a magnetic ballast in the base ( light mass means electronic one) that supplies 12VAC to the lamp. If the lamp has continuity ( less than 2 ohms between the pins) then it is ok, you will need a new ballast or more likely a new socket for the lamp. The sockets do corrode inside, and this then makes it intermittent. When you are placing the lamp in the socket do not handle it with bare hands, and if you have wipe it with a cloth soaked in IPA or acetone to degrease it, otherwise you will find burns on the glass that will degrade it in a short time.105 downlighters at work, all 20W versions of the same lamp with a built in dichroic reflector. If I need the bulbs for the one desk lamp I just break the glass reflector off one carefully, generally 2 out of 3 survive.....

author: G7PSK
author_rank: Super Contributor
timestamp: December 15, 2012, 02:14:22 pm
content: Those quartz halogen bulbs just about always cook the holder to a point where it fails.

author: Boris_yo
author_rank: Frequent Contributor
timestamp: December 16, 2012, 06:00:14 pm
content: ThanksPeterGandSeanBQuote from: G7PSK on December 15, 2012, 02:14:22 pmOh yeah, I once touched it rapidly and it was at least warm and drawing fingers near feels very hot, not to mention warmth emitted from bulb itself. There is a plastic covering bulb and I wondered how it withstands such heat but obviously it is made to. In fact I wondered how bulb itself endures such heat and lasted me several years. On the lamp says that this bulb is JV G4 12V and up to 35W bulb can be installed, however how many Watts was this bulb I don't know since nowhere mentioned. But judging that this desk lamp originally came with this bulb, I reckon it's 35W. Amazon has those but they are selling in bulb while I only need one because I don't often use this lamp hence will try websitePeterGprovided.I see there is frosted bulb and clear bulb. Which is better for reading?

author: codeboy2k
author_rank: Super Contributor
timestamp: December 27, 2012, 08:53:49 pm
content: I had one of these desk lamps. It started getting intermittent, and dependent on the position of the lamp head for it to work.It became frustrating, so I took it apart to see if it was just a loose wire, but nope, the lamp holder really was cooked, disintegrating and corroded to hell.mine was a 50W bulb with a 12V transformer in the base. I wanted to replace it with a pair of 3W LEDs I had laying about, but never got around to that project.it was easier to just buy a new LED desk lamp. Working under that halogen lamp was way too hot , I don't know how I lived with it for so long.

author: SeanB
author_rank: Super Contributor
timestamp: December 28, 2012, 04:37:19 am
content: I replaced the lamp with LED for the dask lamp i have, as it was way too hot to use comfortably. One 1W LED on an old CPU heatsink without the fan fitted in the place of the lamp and reflector assembly nicely with the help of some 5 minute clear epoxy. A old cellphone PSU in place of the transformer in the base, along with a steel block to add mass and a current limiting resistor to set the current and it worked well. Replaced the input capacitors that were bulging with some film units and extra capacitance and it was done, with the film capacitor doing double duty as the mounting of the board as it has a mounting hole.As to the difference between clear and frosted in these small lamp there is not much difference, the frosted just has a smaller more diffused shadow of objecs between the light and the table.

author: Psi
author_rank: Super Contributor
timestamp: December 28, 2012, 04:58:30 am
content: heh, looks like one of those lamps where the 12V is carried to the lamp on the two exposed metal telescopic antennas.See if you can measure 12V on AC range when the lamp is not working across the two telescopic metal bits.If you see 12V AC but the lamp isn't going at least you know the fault is above that point.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 28, 2012, 06:14:53 am
content: bulb like that, if it fails, it fails in one go, meaning it will goes dead right away, no second chance. your intermittent lighting indicates loose switch contact or wire connection. test as per Psi's recommendation, ie putting both DMM probe into the bulb's plug, but be sure to set to "highest mains" range, some bulb will just connected to mains directly so be carefull not to touch any metalic part and not blowing your DMM. if the DMM shows 12V or 120 or 240V (depending on your contry's mains voltage) then the connection is ok, try to move the wire around if the reading jumping up and down to 0V, if it is, it means... loose connection.Quotelol. for good wire, the continuity tester should "beep". if no beep means wire is not good. for resistance test, a good wire is less than 5-10ohm worst, if more ohm, please replace or repair the wire. that test if the bulb is for direct mains with no circuit in between. maybe you can tear down the desk lamp and see whats inside to gain better knowledge of electricity

author: kingjameo
author_rank: Newbie
timestamp: December 28, 2012, 06:36:34 am
content: I believe Plato makes some good tips for Hakko irons.

author: Psi
author_rank: Super Contributor
timestamp: December 28, 2012, 06:45:09 am
content: This is what i mean.Some of these lights use the two metal supports as the 12v conductors.That's why the black spacer is there. So you can't twist the lamp far enough to make the rods touch each other. Doing so would short the supply.

author: peter.mitchell
author_rank: Super Contributor
timestamp: December 28, 2012, 07:44:54 am
content: Quote from: Psi on December 28, 2012, 06:45:09 amwow, that's fricken lazy, i always assumed they ran wire up the inside or something...

author: Monkeh
author_rank: Super Contributor
timestamp: December 28, 2012, 07:56:43 am
content: Quote from: Boris_yo on December 16, 2012, 06:00:14 pmIt's not plastic, it's glass acting as a UV filter.QuoteThe temperature is a fundamental part of the operation. The internal temperature of the lamp is actually often around 2500C, FAR beyond the melting point of steel, copper, ordinary glass, aluminium, or most any other material you're used to.Quote from: peter.mitchell on December 28, 2012, 07:44:54 amIt's actually a lot more durable than running a wire inside. I'll admit I first realised what they were doing when I grabbed one with a wet hand.. Shocking experience.