TV Back-light Spark Gap?

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Likely a dry joint around the HT.....

=A0 =A0 ...Jim Thompson

=A0 =A0| =A0 =A0mens =A0 =A0 |

=A0 | =A0 =A0 et =A0 =A0 =A0|

=A0|

=A0 =A0 =A0 |

Could be plastic thermally 'popping'

Easy first test: outside, compressed air, blow the dust out of it. Difficult second test: Take apart, distilled water/chemical clean up.

I'd go for that first one, since we're in a desert that is known for dust buildup especially around electrostatic HV charges.

Since you didn't mention change in brightness when it pops... First thing I'd try is to plug in headphones and verify it ain't coming out the speaker. Zero cost experiment that might save you a lot of fiddling around. I'd also try the brightness at extremes to see if that changes anything.

Weakest link is the transformer. There's often a tiny cap in series with the CFL. I've seen those go open. Might arc across that. Spider webs cause interesting high voltage symptoms.

You forgot to include sci.electronics.repair

Maybe, but I've never seen that happen. There's not enough power in the LCD inverter to draw much of an arc, much less produce a noisy arc. My guess(tm) is that the switching power supply is on its way out. No clue where it's arcing but a charred PCB in the PS Hi-V section would qualify. Open the back, turn OFF the room lights, and look for the sparks.

If there's a corresonding change in the picture with every pop, it might be the swithcing power supply. If there's a corresponding change in CCFL backlighting brightness, it might be the LCD inverter.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

Turn the swamp cooler down?

Cheers

Maybe I'll just toss it, and buy a bigger TV with LED back-lighting ;-)

Prices are amazing. The 55" flat-screen LCD/LED replacement for this...

was only $1080 ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Another thing that happens is that the caps in the low voltage ps go open. The average voltage is the same, but the peak voltage can go much higher. I've only seen that after the fets in the cfl supply short, but I presume that the CFL voltage goes higher before it fails.

Take it apart immediately, remove the backlight power supply and inspect. The classic problem is the long leads sticking out of the back of the board abrade the plastic shield and start sparking to the EMI shield coating on the case. Clipping the leads and replacing the plastic with a piece of Mylar will fix it. I've done a few of these.

Jon

That would be ecologically incorrect. All you probably need to do to repair your existing TV is open it up, look inside, and see what needs to be replaced or repaired. Plenty of parts available from the equipment cannibals on eBay. Most likely, some bug crawled inside and was fried.

Incidentally, next time you design something, try to make it repairable.

I see those at the local recycler all the time. Have your forklift ready. What's interesting is that I also see LCD TV's at the same recycler, which would suggest a rather short lifetime before something blows. The days of 25+ year TV lifetimes are over. These days, you're lucky if the TV can make it through the warranty period before the electrolytics start bulging. This monitor was only 9 months old:

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

I'm betting on a pinched wire. Some Q-dope might be a quick fix. I had a Samsung CRT that would snap every now and then in warmer weather, but never outright failed.

Cheers

Do CFL's go that high in voltage?

This quits after a few hours of operation ?? ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

Do CFL's go that high in voltage?

***Circa 1200V to strike the CCFL tube - about half that when ionised.

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

They run somewhere around 1k to 5kv depends upon the cfl.

Cheers

Haven't had one of those since 1993. ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

I took a power cut-off saw to it and broke it down into pieces I could lift (total weight ~400#). And scavenged all the nice heatsinks ;-)

Probably the CFL back-light, which is why I went LCD/LED.

...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.

They run somewhere around 1k to 5kv depends upon the cfl.

Cheers

****You can get a definitive answer from the HR (famous for their excellent pattern flyback transformers) backlight inverter datasheets, the datasheet I read said 1200V to strike & 600V ionised - if they do a pattern inverter for the specific TV in question, you can nail it to the spot.

Failing CCFL tubes do not create audible arcs. You would also see flashes, dimming, or an orange colored background if it were the tubes or inverter. Since that wasn't mentioned as a symptom, I'll assume that it's not the tubes or inverter.

What's the maker and model number of your 19" LCD TV? I'll find you a replacement LCD inverter or some repair clues. However, I still think it's something arcing in the switching power supply possibly inspired by bulging electrolytic caps.

1960's "Save a Tree" 2010's "Save an LCD"

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Jim designs integrated circuits. Do you think you can repair them?

From Jeff's responses I think he has a reading comprehension problem :-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
| E-mail Icon at http://www.analog-innovations.com |    1962     |
             
I love to cook with wine.     Sometimes I even put it in the food.