Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old August 7th 03, 03:17 PM
Sofie
 
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Default 21" Monitor problem: Poor brightness. Dell D1626HT/ Sony GDM-500 chassis

Lionel:
You cannot "fix" or "tweak" a weak CRT. In it's previous life, it was
probably left on 24/7 ..... this is most likely why you were able to pick
it up for "cheap" at a market.
A CRT rejuvenator like a B&K or Sencor MIGHT be able to eek some more life
and brightness out of it.

Best Regards,
Daniel Sofie
Electronics Supply & Repair
------------------------------------



snipped:
"Lionel" wrote in message
I just picked up one of these beautiful 21" monitors cheap at a market.
Except for this brightness problem, it works perfectly. I'm driving it


Turning up all the on-screen bias & gain controls to the
maximum values produces a usable, but still darkish image. I was
assuming that as the monitor is about 4 years old, it'd probably just
need a cleanup, & for me to tweak up the EHT, but having obtained a
schematic, I now know that there are *no* internal adjustments at all! I
Any tips or ideas?





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Old August 7th 03, 11:24 PM
Jerry Greenberg
 
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Default 21" Monitor problem: Poor brightness. Dell D1626HT/ Sony GDM-500 chassis

I have seen CRT's go weak where there was a lot of brightness loss,
and yet the pictures were still sharp. I think it is how the tube
deteriates that indicates how it will look. Most of the time, they do
go soft, but not always.

Jerry Greenberg

--


Lionel wrote in message ...
On Thu, 7 Aug 2003 07:17:14 -0700, in
, "Sofie" said:

Lionel:
You cannot "fix" or "tweak" a weak CRT. In it's previous life, it was
probably left on 24/7 ..... this is most likely why you were able to pick
it up for "cheap" at a market.
A CRT rejuvenator like a B&K or Sencor MIGHT be able to eek some more life
and brightness out of it.


Any time I've looked at monitors with worn out CRTs, they've usually had
weak contrast, & a general 'murky' look. This one has a razor sharp,
very clean image, apart from the lack in brightness. (It was running
when I bought it, & I wouldn't have bothered if it'd had a bad looking
image.)

It's worth mentioning that this beast has a digital diags port that's
accessible via a hatch on the rear cover, & that the service guide says
you're supposed to use some sort of proprietory device to do the initial
convergence (etc) setup on it. My guess is that you need it to access
all the adjustments that are normally done with trimmers, etc.

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Old August 8th 03, 04:40 AM
Andy Cuffe
 
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Default 21" Monitor problem: Poor brightness. Dell D1626HT/ Sony GDM-500 chassis

Lionel wrote:

I just picked up one of these beautiful 21" monitors cheap at a market.
Except for this brightness problem, it works perfectly. I'm driving it
with a Matrox 450 Dual Head card at 1600x1200 x 32 bits at 75Hz. It
calibrates correctly with a Spyder, except for the maximum brightness
only being about half of what the calibraation software thinks it should
be (some 93 candles per square metre vs the ~50 candles on this
monitor). Turning up all the on-screen bias & gain controls to the
maximum values produces a usable, but still darkish image. I was
assuming that as the monitor is about 4 years old, it'd probably just
need a cleanup, & for me to tweak up the EHT, but having obtained a
schematic, I now know that there are *no* internal adjustments at all! I
cleaned all the dirt off the HT & EHT components & resoldered a heap of
joints that looked kind of 'dry' but it made no visible difference.

Any tips or ideas?

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------



It's a long shot, but I've seen a couple of sonys with a bad cap in the
CRT heater supply. Make sure you have 6.3 v on the heater. If the CRT
is weak, you might be able to try boosting it a little by using the old
few turns of wire around the flyback core trick. I've never tried to do
this with a monitor though, so I'm not sure if it would work. Most
monitors get the heater supply from the power supply instead of the
flyback. I don't see why it wouldn't work. If there are any resistors
in series with the heater supply, you could try bypassing them with wire
before doing anything else. I've seen quite a few of these with dim
CRTs that still look reasonably sharp. It's a shame that most companies
don't use the power saving features!
--
Andy Cuffe



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