Author Topic: Cold Cathode EOL's  (Read 1264 times)
suzukir122
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suzukir123
Cold Cathode EOL's « on: July 25, 2017, 02:02:36 PM » Author: suzukir122
I was at work one day and a thought randomly popped up in my head... how exactly do most Cold Cathode fluorescent lights
act during EOL? Same question regarding Neon lamps. (like Neon signs, etc) I've never seen either kind of lamp during EOL,
although I have of course seen Neon signs and linear Neons flickering at random.
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Re: Cold Cathode EOL's « Reply #1 on: July 25, 2017, 03:50:42 PM » Author: Ash
From thin (typically T0.8..T1) CCFLs which i relamped in LCD monitors :

Sometimes they develop a very lossy single hot spot on the cathode cup, that glows Incandescent. This spot gets so hot that it pops the Glass near it, so the end with the cup breaks off the tube

Sometimes just their arc voltage goes up excessively or is too unstable, so the CCFL driver shuts down on EOL protection



There used to be a model of an LCD monitor - HP 19 inch, 5:4 aspect ratio, Silver front / Black back - i dont recall the exact model but it was something like L1950 ? which i got to know well from one of the places where i was IT..

Normally LCDs have 4 CCFLs, in 2 series pairs. The center link between the 2 CCFLs is at Earth / low potential (all the current sense resistors etc are there), and between the 2 "HV" ends is the secondary of the HV transformer. The OCV is sufficient to start both lamps in series

In this LCD, they still used the same transformer with 2 secondaries, but connected 1 CCFL to each output (so total 2 CCFLs in the monitor)

As long as the CCFL was ok, it worked normally, it clamped the HV output to its arc voltage

When the CCFL EOL'd, the voltage (in this monitor across a single CCFL output) was sufficient to arc across the connector on the PCB. The circuit then recognized this arc as a working CCFL so the EOL protection never reacted. Those monitors would simply go up in smoke once the CCFL EOL'd

By cutting the carbonized tracks off the PCB and wiring a new CCFL the monitor would be back to working condition.. Until next EOL
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Medved
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Re: Cold Cathode EOL's « Reply #2 on: July 25, 2017, 03:59:49 PM » Author: Medved
I was at work one day and a thought randomly popped up in my head... how exactly do most Cold Cathode fluorescent lights
act during EOL? Same question regarding Neon lamps. (like Neon signs, etc) I've never seen either kind of lamp during EOL,
although I have of course seen Neon signs and linear Neons flickering at random.


Neon lamps: Mostly glass envelope blackening due to sputtering, gas "cleanup" (some important active ingredient gets "hammered" into the electrode material).

CCFL: Seems like atmosphere contamination (the hot spot,...), gas "cleanup" (some important active ingredient gets "hammered" into the electrode material), seal failure (heat from cathodes, repetitive stresses,...), with some design cathode wear (some use just a thin metalic coating on a ceramic substrate as a cathode), some (mainly the short, wider tubes) suffer from tube blackening.
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suzukir122
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Re: Cold Cathode EOL's « Reply #3 on: July 25, 2017, 04:53:57 PM » Author: suzukir122
Ahh lol interesting detail. Maybe one day I can see all of this as it unfolds, although it's been a while
since I've seen Cold Cathode lamps in use in public places.
I remember though a while back when one of my friends use to live in Ohio, he along with his family were
all watching a TV show one day together at their place and I watched the show with them. This was on an old school
flat screen TV with those triphosphor fluorescent lamps that I still have never seen before, that had a 60
or 120 hertz flicker. I don't remember... anyways, although there was no serious flickering, the TV randomly showed
a warning message stating to change one of the lamps. I'm pretty sure you guys know what I'm talking about,
but it's tough for me to explain.
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Re: Cold Cathode EOL's « Reply #4 on: July 25, 2017, 09:36:18 PM » Author: Ash
LCD backlights are not considered replacable. The message would have to read get a new TV
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Medved
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Re: Cold Cathode EOL's « Reply #5 on: July 26, 2017, 01:42:08 AM » Author: Medved
I remember quite large installation in the main hall of Brussel Central train station. There is a dome shape ceiling/roof, from the inside view made of small (compare to the whole hall, absolute size I have no idea at all) square windows. And these windows were each framed by two L shaped fluorescents, and I guessed the were cold cathode type (I can not imagine the maintenance of so huge amount of custom shape lamps placed so high without using some inherently long lasting technology; and out of the 100's lamps, there were really no more than 1 or 2 failures).
Last time I was there (around 2012 or earlier) there was a big modernization overhaul just in proress, so I don't know, if that lighting survived there.
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HomeBrewLamps
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SodiumVapor 105843202020668111118 UCpGClK_9OH8N4QkD1fp-jNw majorpayne1226 187567902@N04/
Re: Cold Cathode EOL's « Reply #6 on: July 29, 2017, 03:25:11 PM » Author: HomeBrewLamps
you should like... check and see sometime... it'd be pretty awesome if they're still there
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suzukir122
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Re: Cold Cathode EOL's « Reply #7 on: July 30, 2017, 06:04:55 AM » Author: suzukir122
I agree!
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Lighting has ALWAYS been a passion of mine. I consider everyone on here to be a friend

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Re: Cold Cathode EOL's « Reply #8 on: July 30, 2017, 11:41:39 AM » Author: Medved
Well, that is a question for someone living in that area, for me the 1000km distance is quite out of reach...
I remember that from the time I was visiting Oudenaarde (at Cebtral I was switching trains from the airport), but I wasn't there already more than a year (and the last time I was switching at Nord, because not that crowdy) and I see no trip in at least another year...
But I will try to ask some of my Belgian colegues once I meet them...

I've just found a photo on Wikipedia, fraction of the ceiling is visible there. But I don't know, if that photo is after or before the reconstruction (if after, it would be a good news, because that means at least the approximate look was kept there...)
« Last Edit: July 30, 2017, 11:50:24 AM by Medved » Logged

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