Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

[budm]

I got this one in today, the backlights come on for second (it shows 'PLEASE WAIT'), the go black. Check the 24V, BL_ENA are OK.
Check the fuse on the inverter, ESR of the caps on the inverter are OK.
Check the DCR of the inverter transformer high voltage windings side, all around 600 Ohms (they are within 1% from each other).
So thought I may have bad lamp.
I grab CCFL and solder a small solid wire to the center of the lamp base.
I touch one pin of the four pin (the inverter high voltage transformer has 4 pins on the high voltage winding side) at a time then turn on the TV to see how my CCFL will light up. I see that the CCFL is lit up partly on one of the winding. The good winding will light the lamp brightly. I remove the transformer, and sure enough, it has burnt winding.
So this is a new trick for finding bad inverter transformer.

[audiofreak19]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

That's a awesome method for testing. so u just hooked up a wire to the point u circled and touched it to the bottom of the light bulb to test it. How did you get the transformer off. Are they just soldered in?

[budm]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

It is just SMD, so I just add more solder to all the pins and just tilt it up.
I solder the solid wire to to the bottom of the CCFL base to use it as the probe.
BTW, I meant to type CFL, not CCFL.

[Alastair E]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

Marvellous!

A nice quick check of backlight-driver boards!

Ive always had a bit of a mind-block on backlight faults--prolly because they do my head in!

[stj]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

that's a 110v cfl lamp,
and i dont understand how it's running.

you could use the tube, or a philips PL tube,
but i dont understand how the cfl runs with an internal rectifier, smoothing cap and invertor in the base!

[tom66]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

Budm is bypassing that and just using the CFL tube.

[stj]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

he dont say that - and that lamp looks unopened.

i'm thinking because he's in the u.s. the lamp is rectifying, smoothing and re-oscillating the power from the invertor.
if it is then his diodes/cap wont last long in the lamp at those frequency's

[tom66]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

see here:
https://www.badcaps.net/forum/showth...er+testing+cfl

[budm]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

The lamp is one of those broken lamp that I solder a solid wire to the base of the lamp and no need to take the lamp apart, it can be 120 0r 230V CFL, the high voltage will just goes through the lamp circuit (due to stray capacitance) and through the lamp glass due to stray capacitance of your body while you are holding it with you hand, Just remember that we are dealing with high frequency AC, any stray capacitance inside the lamp will have low reactance.
Ever try holding the fluorescent lamp close to high frequency generator?
This is an old trick I used to find out if AC High frequency generator is working or not (I used to repair lots of PLASMA Etcher for semiconductor industries), on the high power the lamp does not even have to make contact with the source, just put the glass body close to the source and it will light up.
You can also use this:
http://s807.photobucket.com/user/bud...tml?sort=3&o=1

[stj]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

yea, i'v seen people putting 6foot tubes into the ground under 100,000v powerlines before - very hazardous!

[tom66]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

It's about as hazardous as poking your tongue out 20 foot under a 100kV power line.

[stj]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

unless to stay too long - then you get lukemea or brain tumors.
that's why in most country's your not allowed to build schools or residential property under high-voltage lines.

[tom66]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

50/60Hz, even at many kV or kA, does not cause leukaemia or brain tumours; please stop reading tabloids. Magnetic field at the house falls off by a cube law to be insignificant compared to ordinary household currents. (Remember power-line current about 1000A, household current about 10A through average ring main circuit, distance approx 10x. do the math.) Dirty power etc. I'm not even going to bother that has been debunked so many times over it's not even funny, just google it.

The only reason why you see cases of poorer health around power lines is because poorer people tend to live near them (less desirable housing), and income correlates well with health. Also tends to be families - children are in general more likely to get serious complications earlier with compromised/developing immune system (and the immune system is involved in cancer prevention too.)

Interestingly, same reason why people who eat olives are healthier, not because olives improve health significantly but because wealthier people eat them and wealthier people are generally healthier.

[stj]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

maybe you should look into why the towers have to be so high at that voltage.

[mmartell]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

Sounds like he already explained that.

Thanks for the tip budm !

[mmartell]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

Errr... is it safe to use a WORKING cfl for this test ??

[tom66]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

maybe you should look into why the towers have to be so high at that voltage.

Because V=IR and P=I^2 R so to get lower V drop and hence lower P loss, reducing the cost of electricity, V must be relatively high and I must be relatively low. This is secondary school physics.

[stj]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

high as in meters, not volts.

[tom66]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

The reason is because you don't want sagging power lines to hit trees, buildings, tall trucks/vehicles, or people. Obviously within a few meters of it is risky; arcing is possible to a grounded object.

Have you ever seen how low power lines can go in hot weather, when the lines expand? Also in colder climates, the lines can sag under heavy ice. Power lines also buzz (at 1st & 3rd harmonic mainly) - which can be annoying - so putting them higher reduces this perception.

But the few milligauss magnetic field (at the distance a transmission line is away from the average human) produced by the power line does not affect human health in any way at all. Other than it looking ugly, leading to feelings about that...

[stj]

Re: Dynex DX-40L261A12 using CCFL for locating bad inverter xformer

actually it's because of electromagnetic radiation.
i used to work with "national grid" so dont go saying it's all conspiracy shit.

there are many things that arent safe.
high voltage AC transmision cables,
wifi routers,
cellfone towers & fones,
cfl & halogen lamps!

that doesnt mean we ban them or stop using them - it means we recognise & minimise the dangers.