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Temperature of CCFL transformer in laptop?

Started by Joerg September 21, 2018
A laptop backlight was turning off after a few minutes of work and, 
miracuslously, when turning the laptop off (invokes hibernate) it always 
came back on. I opened the screen, reseated the inverter connectors, so 
far it ran through more than an hour. Here's knocking on wood.

However, I noticed that the transformer core on the CCFL inverter heats 
up to the point where leaving my finger on the shield around it hurts. 
My own inverter designs with CCFL transformers never did that. Is this 
normal in laptops?

-- 
Regards, Joerg

http://www.analogconsultants.com/
On 2018/09/21 10:57 AM, Joerg wrote:
> A laptop backlight was turning off after a few minutes of work and, > miracuslously, when turning the laptop off (invokes hibernate) it always > came back on. I opened the screen, reseated the inverter connectors, so > far it ran through more than an hour. Here's knocking on wood. > > However, I noticed that the transformer core on the CCFL inverter heats > up to the point where leaving my finger on the shield around it hurts. > My own inverter designs with CCFL transformers never did that. Is this > normal in laptops? >
Which make and model laptop? Several Apples (my wife's for example) have issues with the backlight staying on... John :-#)#
On 2018-09-21 13:10, John Robertson wrote:
> On 2018/09/21 10:57 AM, Joerg wrote: >> A laptop backlight was turning off after a few minutes of work and, >> miracuslously, when turning the laptop off (invokes hibernate) it >> always came back on. I opened the screen, reseated the inverter >> connectors, so far it ran through more than an hour. Here's knocking >> on wood. >> >> However, I noticed that the transformer core on the CCFL inverter >> heats up to the point where leaving my finger on the shield around it >> hurts. My own inverter designs with CCFL transformers never did that. >> Is this normal in laptops? >> > > Which make and model laptop? Several Apples (my wife's for example) have > issues with the backlight staying on... >
It's an old Dell Inspiron 1000. Only used for web, movie lists, kitchen recipes and a little personal email, nothing sensitive. 3-1/2h so far and it hasn't quit anymore. I ran a longer Yourtube video which, on that laptop and the "new and improved" Youtube, maxes out the processor power a 100% to get it all toasty. Maybe re-seating the connectors was the trick. Hopefully. I was just very surprised how hot the ferrite gets. -- Regards, Joerg http://www.analogconsultants.com/
Joerg <news@analogconsultants.com> wrote:
> However, I noticed that the transformer core on the CCFL inverter heats > up to the point where leaving my finger on the shield around it hurts. > My own inverter designs with CCFL transformers never did that. Is this > normal in laptops?
It may be that the CCFL is getting old, the working voltage increases over time until the inverter cannot deliver it anymore. Then the tube starts flickering or has trouble to ignite at low temperature. Replacement tubes (and inverters) can easily be found on internet.
On Fri, 21 Sep 2018 10:57:22 -0700, Joerg <news@analogconsultants.com>
wrote:

>A laptop backlight was turning off after a few minutes of work and, >miracuslously, when turning the laptop off (invokes hibernate) it always >came back on. I opened the screen, reseated the inverter connectors, so >far it ran through more than an hour. Here's knocking on wood. > >However, I noticed that the transformer core on the CCFL inverter heats >up to the point where leaving my finger on the shield around it hurts. >My own inverter designs with CCFL transformers never did that. Is this >normal in laptops?
CCFL LCD inverters get warm, but not so hot that you can't keep your finger on the xformer[1]. When it overheats like that, I'm told that it's usually shorted turns on the transformer winding. The reason I said "I'm told" is that I've never investigated the problem and prefer to just replace the LCD inverter with whatever I can find on eBay. However, a shorted turn isn't the only thing that can heat up the xformer. An CCFL tube that's about to die will also cause overheating. You can generally spot those by just looking at the color. If it comes on initially as sorta a red-white color, instead of a solid white color, it's either a bad CCFL tube, bad inverter, or both. I check this by replacing the CCFL lamp with an external test lamp. If it lights instantly to bright white, the inverter is ok. You can also power the LCD panel with an external inverter so check the CCFL lamp. (Troubleshooting by substitution). The Dell Inspiron 1000 is an ancient laptop. The LCD inverter is common, cheap, and easily replaced. <https://www.ebay.com/sch/i.html?_nkw=inspiron+1000+lcd+inverter> [1] If you're fingering the transformer winding, please note that it can have 500 - 700V on it. The kapton tape will probably protect you from shock (500V/mil), but the enamel covered wire windings are problematic, especially if the insulation has been removed by "scratching" the transformer. I did that to myself one, and only once. -- 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
On 2018-09-21 16:28, Rob wrote:
> Joerg <news@analogconsultants.com> wrote: >> However, I noticed that the transformer core on the CCFL inverter heats >> up to the point where leaving my finger on the shield around it hurts. >> My own inverter designs with CCFL transformers never did that. Is this >> normal in laptops? > > It may be that the CCFL is getting old, the working voltage increases > over time until the inverter cannot deliver it anymore. > Then the tube starts flickering or has trouble to ignite at low temperature. > > Replacement tubes (and inverters) can easily be found on internet. >
Might be but it starts immediately, never flickers and no weird hues. -- Regards, Joerg http://www.analogconsultants.com/
On 2018-09-21 16:41, Jeff Liebermann wrote:
> On Fri, 21 Sep 2018 10:57:22 -0700, Joerg <news@analogconsultants.com> > wrote: > >> A laptop backlight was turning off after a few minutes of work and, >> miracuslously, when turning the laptop off (invokes hibernate) it always >> came back on. I opened the screen, reseated the inverter connectors, so >> far it ran through more than an hour. Here's knocking on wood. >> >> However, I noticed that the transformer core on the CCFL inverter heats >> up to the point where leaving my finger on the shield around it hurts. >> My own inverter designs with CCFL transformers never did that. Is this >> normal in laptops? > > CCFL LCD inverters get warm, but not so hot that you can't keep your > finger on the xformer[1]. When it overheats like that, I'm told that > it's usually shorted turns on the transformer winding. The reason I > said "I'm told" is that I've never investigated the problem and prefer > to just replace the LCD inverter with whatever I can find on eBay. > However, a shorted turn isn't the only thing that can heat up the > xformer. An CCFL tube that's about to die will also cause > overheating. You can generally spot those by just looking at the > color. If it comes on initially as sorta a red-white color, instead > of a solid white color, it's either a bad CCFL tube, bad inverter, or > both. I check this by replacing the CCFL lamp with an external test > lamp. If it lights instantly to bright white, the inverter is ok. You > can also power the LCD panel with an external inverter so check the > CCFL lamp. (Troubleshooting by substitution). >
I looked carefully for hue and tint towards the red or purple but nothing, it's nice and white. This laptop isn't used a lot so I'd be surprised if the backlights were already exhausted.
> The Dell Inspiron 1000 is an ancient laptop.
2005 ain't ancient to me. My car is from 1997, my road bike from 1982 and my electric drill is from before the 2nd world war: http://www.analogconsultants.com/ng/sed/olddrill.JPG I had to replace the power cord though.
> ... The LCD inverter is > common, cheap, and easily replaced. > <https://www.ebay.com/sch/i.html?_nkw=inspiron+1000+lcd+inverter> >
Those are the wrong ones. The correct ones are only available used: https://www.ebay.com/itm/Dell-Inspiron-1000-Series-Laptop-LCD-Screen-Inverter-Board-AS023175050-GENUINE/332196573136
> > [1] If you're fingering the transformer winding, please note that it > can have 500 - 700V on it. The kapton tape will probably protect you > from shock (500V/mil), but the enamel covered wire windings are > problematic, especially if the insulation has been removed by > "scratching" the transformer. I did that to myself one, and only > once. >
Oh, I did as well. Designed a board for an optical switch which needed a few hundred volts. Put on the warning on English and Spanish. Guess who got bitten? Me, by my own design. A Chinese engineer could not stop laughing, "Should have had the warning on there also in German and Chinese". -- Regards, Joerg http://www.analogconsultants.com/
"Joerg" <news@analogconsultants.com> wrote in message 
news:g0l1t1Fb65pU1@mid.individual.net...
> Maybe re-seating the connectors was the trick. Hopefully. I was just very > surprised how hot the ferrite gets.
Ferrite often runs at 80-100C where there's a slight core loss minima. Fingers that burn at 50C are a poor judge of hardware that can operate at 100C or 150C or more. Tim -- Seven Transistor Labs, LLC Electrical Engineering Consultation and Design Website: https://www.seventransistorlabs.com/
On 21/09/2018 21:16, Joerg wrote:
> On 2018-09-21 13:10, John Robertson wrote: >> On 2018/09/21 10:57 AM, Joerg wrote: >>> A laptop backlight was turning off after a few minutes of work and, >>> miracuslously, when turning the laptop off (invokes hibernate) it >>> always came back on. I opened the screen, reseated the inverter >>> connectors, so far it ran through more than an hour. Here's knocking >>> on wood. >>> >>> However, I noticed that the transformer core on the CCFL inverter >>> heats up to the point where leaving my finger on the shield around it >>> hurts. My own inverter designs with CCFL transformers never did that. >>> Is this normal in laptops?
Pretty much. Minimising weight for maximised performance is the name of the game so long as they don't cut it so fine that the thing fails.
>> Which make and model laptop? Several Apples (my wife's for example) have >> issues with the backlight staying on... >> > > It's an old Dell Inspiron 1000. Only used for web, movie lists, kitchen > recipes and a little personal email, nothing sensitive. > > 3-1/2h so far and it hasn't quit anymore. I ran a longer Yourtube video > which, on that laptop and the "new and improved" Youtube, maxes out the > processor power a 100% to get it all toasty. > > Maybe re-seating the connectors was the trick. Hopefully. I was just > very surprised how hot the ferrite gets.
Laptops tend to trade weight for heat provided that no external parts can ever get beyond acceptable temperatures. That said I recall some high end Pentium 3 machines tended to cook peoples thighs and sensitive bits if they were actually used in their laps. Mine of that era visibly scarred a varnished desk after a couple of years in the same place. The one that really horrified me when I moved out of Belgium was the PSU for the cable TV & internet which was too mad hot to touch at all and had charred its ratings label to an interesting shade of medium brown. -- Regards, Martin Brown
Martin Brown
>The one that really horrified me when I moved out of Belgium was the PSU >for the cable TV & internet which was too mad hot to touch at all and >had charred its ratings label to an interesting shade of medium brown.
Ha, I just measured the top side of my ziggo cable modem: 69 degrees C! You can burn your fingers on that, and that is while it is doing nothing. Glad to get rid of it, will save on the 'trickety bill.