Re: Trouble with laptop display

From	"Carlos E.R." <robin_listas@es.invalid>
Newsgroups	comp.os.linux.misc, alt.os.linux, alt.comp.os.windows-10
Subject	Re: Trouble with laptop display
Date	2025-07-16 20:42 +0200
Message-ID	<ge8lklxffk.ln2@Telcontar.valinor> (permalink)
References	<7tfkklx99v.ln2@Telcontar.valinor> <1058cvp$p7s3$1@dont-email.me>

Cross-posted to 3 groups.

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On 2025-07-16 16:29, Paul wrote:
> On Wed, 7/16/2025 7:44 AM, Carlos E.R. wrote:
>> Hi,
>>
>> I have an old Compaq Presario CQ61-330SS laptop, which I think I bought around 2010. Battery died, I replaced it, also died eventually. Currently I only use it to watch movies (it has very good internal speakers), when exercising on an static bike.
>>
>> <https://icecat.es/es/p/hp/vk845ea/compaq+presario-laptops-0884962367797-cq61-330ss-3589205.html>
>>
>> Some months ago, the display went black on boot, but closing the lid and opening it again made it work. Today it is impossible, it goes dark instants after opening the lid. I have repeated the operation dozens of times. It happens before booting and keeps doing it after booting. It makes the thing totally unusable.
>>
>> I just replaced the CMOS battery (it reads 3 volts). On boot, it says something about replaced battery, needs to reset, but I don't have time to read what key to press, if any.
>>
>> So that battery was not the problem.
>>
>>
>> Installed system is openSUSE, some old version, I don't remember which. I can not ssh to it, says
>>
>> cer@Telcontar:~> ssh root@minas-tirith
>> Bad server host key: Invalid key length
>> cer@Telcontar:~>
>>
>> It also has Windows.
>>
>> But the problem happens before booting, so the operating system is not involved.
>>
>>
>> What do you think may be going on?
>>
> 
> If the unit has an intensity control, such as one of the old dial-adjust ones,
> that will reduce the electrical load of the CCFL backlight, to keep it lit.

No, no such thing.

I recall having adjusted intensity on software, but I don't think it was 
this laptop.

> Devices where the intensity control is a OSD control, well, it's going to be
> pretty hard to see the screen and turn down the intensity. On some panels,
> holding a strong light near the back of the disassembly, may allow seeing
> the OSD.
> 
> It's something like this. Only a small panel uses a single CCFL.
> 
>                                        700-1000VAC 25KHz Sine wave
>        14.4VDC ------ inverter-board ------------------------------- CCFL tube (inside panel ?)

Ah, yes.

> 
> 
> "How to Replace a Compaq Presario CQ61 LCD Inverter"
> 
>     https://www.youtube.com/watch?v=gZ8uAvI7JBk
> 
> The inverter board has a "strike" voltage (1000V) and this causes the initial conduction
> in the (cold) CCFL backlight tube. The tube warms enough so the trace mercury is vaporized a bit.
> As the tube warms, it conducts more current (3mA) and the inverter board responds
> by dropping the voltage to, say, 700 VAC. The 700VAC in this case, is termed the
> "burn" voltage and is the normal operating voltage as the thing stabilizes. It
> can take 20 minutes, for the optical properties of a CCFL to settle completely
> (instructions on my scanner).
> 
> The inverter is power limited. If at this point, the inverter is in a weakened
> state, or, the CCFL is drawing more than normal, the inverter can shut off in
> response. It goes from driving 700V to 0V.
> 

Right.

> More modern laptops use LEDs for backlight. The LEDs edge-light a piece of some
> sort of plastic that distributes the edge light. This can make shadows or blooming
> along one edge. One of the problems with the idea of LED backlights, is the LED
> backlight area has poor cooling. The LED area can get hot enough, to melt the
> plastic diffuser element, ruining the smooth distribution of the light. So while
> on the surface, a LED based solution seems the reliable choice, it really has
> its own set of issues and is not a perfect solution. The LED output drops with
> age, in the same way that the CCFL tube output drops with age (the display
> color turns brown, if you actually wear out a CCFL tube). CCFL and LED can last
> for 25,000 hours. The electrodes on the CCFL, sputter onto the glass, which
> yields a brown color for the light output at 25000 hours.

No, I did not notice degradation.


> Large displays in the past, had as many as 16 CCFL tubes, at about 3 watts each.
> This used to throw off enough infrared, as you walked past the display when
> the display was on, you could "feel" the heat hit your face, from the raft of
> CCFL tubes. It might take four quads to drive that many CCFL, or eight dual output
> inverters to do the job. If a single inverter dies on one of those, the screen is
> not completely black.

I see, but this machine is not that big. Let me see, the display is 
35cm*20cm.

> 
> The inverters are AC coupled to the CCFL tube. With 2kV capacitors. This means
> the amount of coupling required, the caps might only be 33pF or so. A very tiny
> capacitance. If there is any "foil" in the area of the tube (which you likely
> won't be working on in this case), do not bend/fold/mutilate the foil, since
> the foil also represents a capacitance. Messing with the foil, when the designer
> intended the foil to couple to the tube a bit, causes the tube to malfunction
> with your new inverter. When an inverter is a dual or a quad, there are more HV
> connectors and coupling caps for the tube(s) connected.
> 
> So why all the goofy care, about "sine waves" and shit ? The tube cannot have
> a DC component across it. Only AC may be applied to the tube. The sloshing
> of AC, helps reduce the damage to the CCFL electrodes over lifetime. This is
> why the thing is specified with sine wave drive. By modulating the inverter,
> and not putting out continuous sine waves, you can achieve dimming... without
> changing the peak voltage, and this keeps the CCFL in "burn" state when
> the intensity is set to lower values.   _XXXXXX______XXXXXX______XXXXXX_
> Those are bursts of 25KHz sine waves, 50% intensity.
> 
> I don't know if you can get at the tube-area for your LCD panel, but
> after viewing the video above, you can bet it would be a bear to get at :-)

No, I would try to find some shop to do it, I'm not up to the task.

Or, I would garbage the thing and get something else. Maybe a tablet. Or 
get a second hand laptop.

Hum, I do have a 32 bit old laptop somewhere.

> 
> Summary: Reduce electrical load on inverter, by reducing the intensity setting.
>           This will give about three weeks of service, before it quits for good.
> 
>           The video has a baggy with a part number on it. That could be the
>           inverter they are trying to sell to people.
> 
>           Inverters and tubes, work as a pair. The characteristics should match.
>           The CCFL tube is unlikely to have a part number on it. If the inverter
>           has the wrong capacity, it could overdrive or underdrive the CCFL and so on.
>           It's not a well-specified area, except for a person who does a lot of
>           these, and they feel they have the right "generic" inverter for the job.
>           Some CCFL tubes are longer than others, the "strike" voltage is slightly
>           different and so on. The foils must be put back as you found them.
> 
>           A USENETter in sci.electronics, wrote an entire book about this, and
>           the book was provided free by his employer. That's where I got the hint
>           about the foils, and how some lighting designers, don't actually understand
>           how the CCFL circuit works. And the results are comedic failures for other
>           people to try and fix.

Not keen on trying, so thanks for the description. :-)

[...]

Following on VanguardLH hint, it is the backlight.

-- 
Cheers, Carlos.

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Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-16 13:44 +0200
  Re: Trouble with laptop display Marco Moock <mm@dorfdsl.de> - 2025-07-16 14:00 +0200
    Re: Trouble with laptop display Java Jive <java@evij.com.invalid> - 2025-07-16 13:22 +0100
    Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-16 20:43 +0200
      Re: Trouble with laptop display Marco Moock <mm@dorfdsl.de> - 2025-07-17 08:06 +0200
        Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-17 12:16 +0200
  Re: Trouble with laptop display Arkadiusz 'Black Fox' Artyszuk <blackfox_pl@protonmail.com> - 2025-07-16 14:20 +0200
  Re: Trouble with laptop display Robert Heller <heller@deepsoft.com> - 2025-07-16 12:39 +0000
  Re: Trouble with laptop display Herbert Kleebauer <klee@unibwm.de> - 2025-07-16 14:43 +0200
  Re: Trouble with laptop display Paul <nospam@needed.invalid> - 2025-07-16 10:29 -0400
    Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-16 20:42 +0200
  Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-16 16:49 +0100
  Re: Trouble with laptop display VanguardLH <V@nguard.LH> - 2025-07-16 11:52 -0500
    Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-16 20:41 +0200
      Re: Trouble with laptop display Java Jive <java@evij.com.invalid> - 2025-07-16 21:11 +0100
        Re: Trouble with laptop display Paul <nospam@needed.invalid> - 2025-07-16 17:21 -0400
      Re: Trouble with laptop display "J. P. Gilliver" <G6JPG@255soft.uk> - 2025-07-16 20:12 +0100
        Re: Trouble with laptop display Paul <nospam@needed.invalid> - 2025-07-16 17:15 -0400
        Re: Trouble with laptop display not@telling.you.invalid (Computer Nerd Kev) - 2025-07-17 09:10 +1000
      Re: Trouble with laptop display Jack <Jack@invalid.invalid> - 2025-07-16 19:09 +0000
        Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-16 22:30 +0200
          Re: Trouble with laptop display Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-07-16 16:58 -0700
            Re: Trouble with laptop display Robert Heller <heller@deepsoft.com> - 2025-07-17 01:58 +0000
              Re: Trouble with laptop display Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-07-17 03:29 +0000
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-17 12:21 +0200
      Re: Trouble with laptop display VanguardLH <V@nguard.LH> - 2025-07-16 18:12 -0500
      Re: Trouble with laptop display Paul in Houston TX <Paul@Houston.Texas> - 2025-07-16 20:42 -0500
      Re: Trouble with laptop display "J.O. Aho" <user@example.net> - 2025-07-17 08:34 +0200
      Re: Trouble with laptop display c186282 <c186282@nnada.net> - 2025-07-17 03:37 -0400
        Re: Trouble with laptop display "J. P. Gilliver" <G6JPG@255soft.uk> - 2025-07-17 10:16 +0100
          Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-17 13:00 +0200
            Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-17 13:50 +0100
              Re: Trouble with laptop display "J. P. Gilliver" <G6JPG@255soft.uk> - 2025-07-17 17:04 +0100
                Re: Trouble with laptop display VanguardLH <V@nguard.LH> - 2025-07-17 13:11 -0500
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-17 20:25 +0200
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-17 19:58 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 08:51 +0200
                Re: Trouble with laptop display Simon <SimonJ@eu.invalid> - 2025-07-18 06:04 +0000
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-18 11:12 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 12:48 +0200
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-18 13:31 +0100
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-17 19:57 +0100
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-17 19:50 +0100
            Re: Trouble with laptop display VanguardLH <V@nguard.LH> - 2025-07-17 13:04 -0500
              Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-17 20:29 +0200
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-17 19:56 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 09:01 +0200
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-18 11:14 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 12:26 +0200
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-18 13:29 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 21:18 +0200
                Re: Trouble with laptop display VanguardLH <V@nguard.LH> - 2025-07-17 16:22 -0500
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 09:13 +0200
                Re: Trouble with laptop display "J. P. Gilliver" <G6JPG@255soft.uk> - 2025-07-18 10:53 +0100
                Re: Trouble with laptop display VanguardLH <V@nguard.LH> - 2025-07-18 18:47 -0500
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-19 02:12 +0200
                Re: Trouble with laptop display Hank Rogers <Hank@nospam.invalid> - 2025-07-18 19:53 -0500
                Re: Trouble with laptop display VanguardLH <V@nguard.LH> - 2025-07-18 20:45 -0500
                Re: Trouble with laptop display Hank Rogers <Hank@nospam.invalid> - 2025-07-18 21:22 -0500
                mini-PC (was: Trouble with laptop display) Frank Slootweg <this@ddress.is.invalid> - 2025-07-18 19:58 +0000
                Re: mini-PC "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 22:28 +0200
                Re: mini-PC (was: Trouble with laptop display) c186282 <c186282@nnada.net> - 2025-07-18 23:38 -0400
            Re: Trouble with laptop display Robert <invalid@invalid.invalid> - 2025-07-17 21:56 +0000
              Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 09:49 +0200
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 11:08 +0200
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-18 11:11 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 12:22 +0200
                Re: Trouble with laptop display Jack <Jack@invalid.invalid> - 2025-07-18 20:24 +0000
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-18 22:05 +0100
                Re: Trouble with laptop display Paul <nospam@needed.invalid> - 2025-07-18 18:31 -0400
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-19 00:50 +0100
                Re: Trouble with laptop display "J. P. Gilliver" <G6JPG@255soft.uk> - 2025-07-19 01:35 +0100
                Re: Trouble with laptop display Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-07-18 19:42 -0700
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-19 15:11 +0200
                Re: Trouble with laptop display Simon <SimonJ@eu.invalid> - 2025-07-19 13:36 +0000
                Re: Trouble with laptop display not@telling.you.invalid (Computer Nerd Kev) - 2025-07-20 09:55 +1000
                Re: Trouble with laptop display rbowman <bowman@montana.com> - 2025-07-20 02:02 +0000
                Re: Trouble with laptop display Daniel70 <daniel47@eternal-september.org> - 2025-07-20 21:10 +1000
                Re: Trouble with laptop display Simon <SimonJ@eu.invalid> - 2025-07-20 05:00 +0000
                Re: Trouble with laptop display Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-07-19 21:43 -0700
                Re: Trouble with laptop display rbowman <bowman@montana.com> - 2025-07-20 05:29 +0000
                Re: Trouble with laptop display Paul <nospam@needed.invalid> - 2025-07-20 07:34 -0400
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-20 21:04 +0200
                Re: Trouble with laptop display Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-07-20 14:40 -0700
                Re: Trouble with laptop display Paul <nospam@needed.invalid> - 2025-07-20 20:43 -0400
                Re: Trouble with laptop display rbowman <bowman@montana.com> - 2025-07-21 04:42 +0000
                Re: Trouble with laptop display rbowman <bowman@montana.com> - 2025-07-20 19:50 +0000
                Re: Trouble with laptop display Daniel70 <daniel47@eternal-september.org> - 2025-07-21 19:41 +1000
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-21 12:16 +0200
                Re: Trouble with laptop display Daniel70 <daniel47@eternal-september.org> - 2025-07-21 22:26 +1000
                Re: Trouble with laptop display Charlie Gibbs <cgibbs@kltpzyxm.invalid> - 2025-07-21 17:35 +0000
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-21 19:55 +0200
                Re: Trouble with laptop display Paul <nospam@needed.invalid> - 2025-07-21 17:37 -0400
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-22 00:36 +0200
                Re: Trouble with laptop display Daniel70 <daniel47@eternal-september.org> - 2025-07-22 19:57 +1000
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-22 12:08 +0200
                Re: Trouble with laptop display Daniel70 <daniel47@eternal-september.org> - 2025-07-22 21:38 +1000
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-22 12:46 +0100
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-20 12:54 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-20 20:55 +0200
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-20 20:22 +0100
                Re: Trouble with laptop display rbowman <bowman@montana.com> - 2025-07-20 19:54 +0000
                Re: Trouble with laptop display Simon <SimonJ@eu.invalid> - 2025-07-21 09:02 +0000
                Re: Trouble with laptop display Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-07-19 21:44 -0700
                Re: Trouble with laptop display Java Jive <java@evij.com.invalid> - 2025-07-20 13:41 +0100
                Re: Trouble with laptop display "J. P. Gilliver" <G6JPG@255soft.uk> - 2025-07-20 17:52 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-20 21:05 +0200
                Re: Trouble with laptop display rbowman <bowman@montana.com> - 2025-07-20 19:56 +0000
                Re: Trouble with laptop display Java Jive <java@evij.com.invalid> - 2025-07-21 12:55 +0100
                Re: Trouble with laptop display Bobbie Sellers <bliss-sf4ever@dslextreme.com> - 2025-07-20 15:00 -0700
                Re: Trouble with laptop display Robert Riches <spamtrap42@jacob21819.net> - 2025-07-22 02:43 +0000
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 23:25 +0200
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-19 00:07 +0200
                Re: Trouble with laptop display The Natural Philosopher <tnp@invalid.invalid> - 2025-07-18 11:08 +0100
                Re: Trouble with laptop display "Carlos E.R." <robin_listas@es.invalid> - 2025-07-18 21:22 +0200

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