12 Mar
2004
12 Mar
'04
1:06 a.m.
posted to sci.electronics.repair, but some of you guys might be able to
help too...
I've just been given a nice Iiyama 21" screen for free which seems to
run quite happily, with the exception that the colours are screwed in
the bottom-right inch or so of the display; the same sort of effect that
would be achieved by holding a big magnet in that corner of the screen.
Degaussing seems to have variable effect; sometimes it almost cures it
and sometimes it just makes it worse, but it never goes away.
Any ideas what might be up with it? Or is it a mechanical fault (i.e.
the picture tube just shot)?
Also, is this something that will get worse now it's started? If not, I
could almost live with replacing the 17" screen on my desktop PC with
this one, as the 17" is getting a little fuzzy and at least this 21"
screen has a crisp display even if there is a bit of colour damage right
in the
corner...
cheers
Jules
12 Mar
12 Mar
1:35 a.m.
-----Original Message-----
From: cctalk-bounces(a)classiccmp.org
[mailto:cctalk-bounces@classiccmp.org] On Behalf Of Jules Richardson
Sent: 12 March 2004 12:07
To: cctalk(a)classiccmp.org
Subject: monitor with screwed colour in bottom-right of screen
posted to sci.electronics.repair, but some of you guys might
be able to help too...
I've just been given a nice Iiyama 21" screen for free which
seems to run quite happily, with the exception that the
colours are screwed in the bottom-right inch or so of the
display; the same sort of effect that would be achieved by
holding a big magnet in that corner of the screen.
I had the same problem with a 21" Digital job I rescued from Compaq since it
was on its way to the dumpster. I lived with it for a while until I
discovered the 'advanced' settings on the OSD, followed by something called
'purity' that directly affected the colours on the diagonals of the tube.
Assuming that the Iiyama is a Trinitron tube like the DEC one you might have
a similar setting.
Later it started flickering and dimming, but that's another story :)
Cya
w
2:26 a.m.
On Fri, 2004-03-12 at 12:35, Witchy wrote:
I had the same problem with a 21" Digital job I
rescued from Compaq since it
was on its way to the dumpster. I lived with it for a while until I
discovered the 'advanced' settings on the OSD, followed by something called
'purity' that directly affected the colours on the diagonals of the tube.
Assuming that the Iiyama is a Trinitron tube like the DEC one you might have
a similar setting.
Ooh, thanks - I'll give that a go. I'm sure it does have that option. It
certainly has vertical convergance which is nice; that's what started
drifting on my 17" screen (with no user control to tweak it) - I fiddled
with the back of the tube and got things back to normal but now it's
going again and prolonged use gives me a headache :/ Hence I'm looking
for a swap at the moment anyway.
Later it started flickering and dimming, but
that's another story :)
Well this one apparently had "wonky colours" according to the chap I got
it from, but I'm sure I made things worse shipping it home. It broke
free of its moorings whilst going round a sharp corner - one very heavy
monitor somersaulted across the boot of the car with one hell of a bang
:-(
I'm amazed the tube didn't implode to be honest, or I didn't smash any
of the boards. Net damage seems to be the loss of a 4" chunk of plastic
from front of the casing...
I am curious as to what the thin cable around the very front of the
screen is supposed to do. That got somewhat battered when the case
smashed. I currently have the plastic case off (and hence this wire
uplugged) whilst I glue it back together, and out of curiousity powered
the monitor up. It came up with a nice crisp normal image. Odd. Probably
coincidence... it does suggest that whatever the problem is is fixable
though (unless something's loose inside the tube itself I suppose)
cheers
Jules
11 Mar
11 Mar
9:44 p.m.
On 12 Mar 2004, Jules Richardson wrote:
I'm amazed the tube didn't implode to be
honest, or I didn't smash any
of the boards. Net damage seems to be the loss of a 4" chunk of plastic
from front of the casing...
CRTs are amazingly tough. I've dropped more than a few on accident from
4-5 feet and they usually just bounce. Normally the enclosure gets
damaged but the CRT--even the neck--stays intact. Only one television
stands out in my memory that fell flat on its face from a height of about
2-3' and imploded, but that was the exception.
--
Sellam Ismail Vintage Computer Festival
------------------------------------------------------------------------------
International Man of Intrigue and Danger http://www.vintage.org
[ Old computing resources for business || Buy/Sell/Trade Vintage Computers ]
[ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]
12 Mar
12 Mar
3:52 a.m.
This is fixable. It is caused when some material is
magnetized. The process to fix it is called
'demagnetizing'. The theory is simple: You apply a
changin magnetic field (for example, that created by a
coil with 60Hz AC), and graduately decrease the
strength of the magnetic field (for example, you pull
the coil further away from the monitor while moving it
in circle). It will fix the problem. Some monitor or
TV has build in circuit to perform the process.
vax3900
--- Jules Richardson <julesrichardsonuk(a)yahoo.co.uk>
wrote:
On Fri, 2004-03-12 at 12:35, Witchy wrote:
__________________________________
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Yahoo! Search - Find what you’re looking for faster
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I had the same problem with a 21" Digital
job I
rescued from Compaq since it
was on its way to the dumpster. I lived with it
for a while until I
discovered the 'advanced' settings on the
OSD,
followed by something called
'purity' that directly affected the
colours on the
diagonals of the tube.
Assuming that the Iiyama is a Trinitron tube like
the DEC one you might have
a similar setting.
Ooh, thanks - I'll give that a go. I'm sure it does
have that option. It
certainly has vertical convergance which is nice;
that's what started
drifting on my 17" screen (with no user control to
tweak it) - I fiddled
with the back of the tube and got things back to
normal but now it's
going again and prolonged use gives me a headache :/
Hence I'm looking
for a swap at the moment anyway.
Later it started flickering and dimming, but
that's another story :)
Well this one apparently had "wonky colours"
according to the chap I got
it from, but I'm sure I made things worse shipping
it home. It broke
free of its moorings whilst going round a sharp
corner - one very heavy
monitor somersaulted across the boot of the car with
one hell of a bang
:-(
I'm amazed the tube didn't implode to be honest, or
I didn't smash any
of the boards. Net damage seems to be the loss of a
4" chunk of plastic
from front of the casing...
I am curious as to what the thin cable around the
very front of the
screen is supposed to do. That got somewhat battered
when the case
smashed. I currently have the plastic case off (and
hence this wire
uplugged) whilst I glue it back together, and out of
curiousity powered
the monitor up. It came up with a nice crisp normal
image. Odd. Probably
coincidence... it does suggest that whatever the
problem is is fixable
though (unless something's loose inside the tube
itself I suppose)
cheers
Jules
11 Mar
11 Mar
9:46 p.m.
On Fri, 12 Mar 2004, SHAUN RIPLEY wrote:
This is fixable. It is caused when some material is
magnetized. The process to fix it is called
'demagnetizing'. The theory is simple: You apply a
changin magnetic field (for example, that created by a
coil with 60Hz AC), and graduately decrease the
strength of the magnetic field (for example, you pull
the coil further away from the monitor while moving it
in circle). It will fix the problem. Some monitor or
TV has build in circuit to perform the process.
In my experience, this is a lot trickier than it sounds. I would first
practice on a CRT that you aren't fond of before moving on to the one
you're trying to rehabilitate.
--
Sellam Ismail Vintage Computer Festival
------------------------------------------------------------------------------
International Man of Intrigue and Danger http://www.vintage.org
[ Old computing resources for business || Buy/Sell/Trade Vintage Computers ]
[ and academia at www.VintageTech.com || at http://marketplace.vintage.org ]
12 Mar
12 Mar
8:36 a.m.
This is fixable. It is caused when some material is
magnetized. The process to fix it is called
'demagnetizing'. The theory is simple: You apply a
changin magnetic field (for example, that created by a
coil with 60Hz AC), and graduately decrease the
strength of the magnetic field (for example, you pull
the coil further away from the monitor while moving it
in circle). It will fix the problem. Some monitor or
TV has build in circuit to perform the process.
In my experience, this is a lot trickier than it
sounds. I would
first practice on a CRT that you aren't fond of before moving on to
the one you're trying to rehabilitate.
Coils for CRTs are wrapped in electrical tape and shaped to suit to
hug the CRT. Electrical tape they used can be any color, rarely see
one with off the beaten trail color like yellow, blue etc.
In tritron CRT monitors especially high end, it has many coils around
the back of CRT, one is degaussing, at least 2 thinner coils for
purity compensation, one round coil near CRT yoke for
picture rotation (common to many monitors also found in some direct
view TVs.)
Sounds like the purity compensation circuit isn't working, check that
your monitor compass module is working. Yes there are few monitors
has one uses it for automatic purity adjustments when monitor is
facing in different direction.
How I know? Fixed an high end sony 21" monitor with that feature.
It was bad compass module IC, more precise, a pin corroded off, fixed
that by grinding away black package and solder short strand of to
make connection. Compass module board is usually horizontal and
almost centered where the base axis is.
Cheers,
Wizard
--
Sellam Ismail Vintage Computer Festival
13 Mar
13 Mar
10:22 a.m.
On Fri, 2004-03-12 at 19:36, jpero(a)sympatico.ca wrote:
Sounds like the purity compensation circuit isn't
working, check that
your monitor compass module is working. Yes there are few monitors
has one uses it for automatic purity adjustments when monitor is
facing in different direction.
How I know? Fixed an high end sony 21" monitor with that feature.
It was bad compass module IC, more precise, a pin corroded off, fixed
that by grinding away black package and solder short strand of to
make connection. Compass module board is usually horizontal and
almost centered where the base axis is.
Funnily enough, I'm using the screen right now, just to see how good it
is for prolonged use. The display is almost perfect in the position that
I want to sit it on my desk - after reading your post I just tried
rotating it and the problem does indeed get worse depending on which
direction the screen is facing.
Whether the screen has such a compass module which is faulty (first time
I've ever heard of such a thing!) or whether it's just down to natural
magentic fields I don't know. I never realised the orientation of a
screen could have such an effect on the output though!
I need to find some good test patterns and then go tweaking a little -
the focus could do with a tiny adjustment IMHO anyway. (There's a 3-way
switch inside the monitor; I was hoping one position was for some kind
of built in test mode but it seems not)
cheers
Jules
12 Mar
12 Mar
4:07 a.m.
On Friday 12 March 2004 08:26, Jules Richardson wrote:
Well this one apparently had "wonky colours"
according to the chap I
got it from, but I'm sure I made things worse shipping it home. It
broke free of its moorings whilst going round a sharp corner - one
very heavy monitor somersaulted across the boot of the car with one
hell of a bang
I am curious as to what the thin cable around the very front of the
screen is supposed to do. That got somewhat battered when the case
smashed. I currently have the plastic case off (and hence this wire
That's the degaussing cable - what removes stray magnetism from the
monitor on power-up/pressing of a 'degauss' button. In fact, a
slightly magnetized monitor could cause some color shifting. You might
try finding an external degausser and trying that as well. Just make
sure you do it away from any magnetic media.
(And in a strange coincidence, a song called "Magnetic" from a local
band I like is playing right now on from the playlist queue. Hmm...)
Pat
--
Purdue University ITAP/RCS --- http://www.itap.purdue.edu/rcs/
The Computer Refuge --- http://computer-refuge.org
4:25 a.m.
On Friday 12 March 2004 10:16, Jules Richardson wrote:
Hmm. Perhaps a picture would help...
Pat
--
Purdue University ITAP/RCS --- http://www.itap.purdue.edu/rcs/
The Computer Refuge --- http://computer-refuge.org
That's the
degaussing cable - what removes stray magnetism from the
monitor on power-up/pressing of a 'degauss' button.
I thought that was the thicker cable running round the edge of the
screen? 
4:11 a.m.
> I've just been given a nice Iiyama 21"
screen for free which
> seems to run quite happily, with the exception that the
> colours are screwed in the bottom-right inch or so of the
> display; the same sort of effect that would be achieved by
> holding a big magnet in that corner of the screen.
No problem, the shadow mask inside the CRT is magnetized. Using a Weller
soldering gun, just pull the trigger and hold the Weller sideways to the
screen and move around in the area of the funny colors, and then pull the
Wellwr away from the screen while still squeezing the trigger. That
should cure the problem.
You might listen and determine if the auto-degauss circuitry is working.
You should here a strange thump/thud when you first turn on the monitor --
if not the degausssing coil isn't working right. There is a
thermistor/varistor that when cold puts 110v AC into a coil of wire around
the CRT. This is a very common failure in both monitors and television
sets.
Gary Hildebrand
St. Joseph, MO
1:07 p.m.
posted to sci.electronics.repair, but some of you guys might be able to
help too...
I've just been given a nice Iiyama 21" screen for free which seems to
run quite happily, with the exception that the colours are screwed in
the bottom-right inch or so of the display; the same sort of effect that
would be achieved by holding a big magnet in that corner of the screen.
This is called a purity problem. There are basically 3 sets of
adjustments to a colour CRT/monitor over and above the ones for a
monochrome CRT :
Purity : Getting the red beam to only hit red phosphor, etc
Convergence : Getting the beams to hit dots next to each other
Grey Scale Tracking : Getting the relative intensities of the colours
correct (so that grey/white are neutral colours)
Gettign the purity correct depends on having a good shadowmask (or
equivalent in Trinitron, etc CRTs -- all these tubes work on essentially
the smae principles!). You then use magnets on the CRT neck to deflect
the beams slightly. Normally you set the thing up displaying a pure red
raster, at which point you hope the other colours are right too!
After setting the purity, you then have to do the convergence. This is
set (on modern CRTs) with more magnetic rings on the CRT neck, and also
by tilting the yoke slightly. I can remember, though, when there were a
dozen or more electrical convergence controls, and when you had to set up
the monitor in the position it was going to be used. Mind you, the
results were worth it (I've nver seen a modern TV that has as good a
convergence as my old Delta-gun Barco!).
Degaussing seems to have variable effect; sometimes it almost cures it
and sometimes it just makes it worse, but it never goes away.
You mentioned in another message that this monitor has suffered physcial
damage. And I may therefore have some bad news for you.
Try hitting (carefully!) that corner of the CRT with the palm of your
hand when the monitor is on. Do the colours change, and end up different?
If so, then I suspect damage to the shaddowmask or its fixing (I seem to
rememebr this is a Trinitron tube, the mask in those is a whole lot of
thin 'wires' running veritcally down the CRT).
Nothing much can be done about this short of a new CRT (even rugunning
places can't normally fix this).
-tony
7437
days inactive
7438
days old
12 comments
8 participants
participants (8)
-
ard＠p850ug1.demon.co.uk -
ghldbrd＠ccp.com -
jpero＠sympatico.ca -
julesrichardsonuk＠yahoo.co.uk -
pat＠computer-refuge.org -
vax3900＠yahoo.com -
vcf＠siconic.com -
witchy＠binarydinosaurs.co.uk