[ltp] T61 screen flickering (backlight tube)

[Keith Lofstrom]

On Wed, Apr 28, 2021 at 11:20:14AM +0200, Hendrik-Jan Heins wrote:
> Apperently in these it is related to broken capacitors in the power
> supply for the backlight.

On Tue, 27 Apr 2021 21:01:32 +0200 (CEST) tomtom at tutanota.com wrote:
> with turned up brightness. Also, sometimes areas that should for
> example be white turn a bit pinkish or even orange, mostly just for a

I sent a more extensive writeup and suggestions to tomtom,
but the
       "areas turn pinkish or even orange"
is the Big Clue - that means the backlight tubes are
producing colored rather than white light,

The pixel array is probably not responsible, and the power
supply can't change the /color/ of the light.

My wild guess is that tomtom's backlight is a fluorescent
lamp (or lamps top and bottom?), resembling the ancient
tube lamps over my office desk.  However, unlike those big
overhead lamps, the volume of the spagetti-thin backlight
tubes is tiny, and the "end seal to volume ratio" of
backlight tube is enormous.

The mechanical stresses on the backlight ends are much
higher --- imagine shaking your office (scaled) the way
you shake your laptop and screen.

So in time, I would expect those backlight end seals to
leak a wee bit of air into a much "wee-er" backlight tube
internal volume.  That will add the light emission lines
of oxygen and nitrogen (yellow and red?) to the mercury
vapor UV emission lines (which excites the phosphor).

The extra emission will also increase the current draw
of the backlight tube (it is discharging both mercury
atoms and the air atoms), electrically stressing the
inverter that drives it.  So that will go soon as well.

That is a very elaborate wild guess. 

Bottom line - replace the tubes, maybe the inverters too.

I suggested tomtom look for an archive of Xiphont's LED
replacement kit from many years past.  tomtom (or one of
you) should consider spearheading an effort to make some
replacement LED strips and sell them (with instructions
to the rest of us.  More brightness, more efficiency, no
leaky glass tube, no high voltage inverter.

I'd gladly buy a dozen kits at semi-reasonable price; $200?

I hope to keep using my 4x3 T60s and X61s for a few more
decades, replacing ancient components (including the
motherboard? The batteries and connectors?) with new
tech as it becomes available. 

A future of chicklet-key runt-screen throwaways and
electronic toxic waste may be content-consumer utopia
for some, but it is my idea of hell.

Keith

P.S.  As my office fluorescent tubes fail, I replace those
with LED tubes as well.  Three times the out-of-pocket
cost, but I expect the LED tubes to last three times
longer, and not generate toxic waste at end-of-life.  Also,
fewer toxic consequences when the next Cascadia Subduction
Zone earthquake happens (very seldom, but guesstimated
Richter 9.5).  40 fluorescent tubes breaking and spilling
their mercury will turn my damaged office into a superfund
site.

-- 
Keith Lofstrom          keithl at keithl.com