CRT image shrinks and grows with changes to brightness
 

I have a 7-year-old 15" CRT monitor that is connected to a standard PC.
Lately I noticed that the size of the monitor's onscreen image is
affected by changes to the image's brightness (the brighter the wider).

For example, my Desktop background is dark. If I click to maximize a
white window, the onscreen image expands by (approximately) 1mm on
every border. If I then click to minimize the window, restoring the
dark Desktop, the image contracts to its previous state. The same
occurs when the monitor's Contrast control is quickly rotated from one
end to the other.

Is this behavior normal or a sign of a dirty or aged CRT? And speaking
old CRTs, would it be wise, with respect to health or sight risks, to
continue to use this monitor as long as it's operating properly (as the
average user would say)?

Dave

Hello, !
You wrote on 14 Jul 2005 08:58:37 -0700:

da For example, my Desktop background is dark. If I click to maximize a
da white window, the onscreen image expands by (approximately) 1mm on
da every border. If I then click to minimize the window, restoring the
da dark Desktop, the image contracts to its previous state. The same
da occurs when the monitor's Contrast control is quickly rotated from one
da end to the other.

da Is this behavior normal or a sign of a dirty or aged CRT? And speaking
da old CRTs, would it be wise, with respect to health or sight risks, to
da continue to use this monitor as long as it's operating properly (as the
da average user would say)?


This symptom is a sign of faulty HT regulation. not the CRT. It can be
fixed, but I wouldn't bother with an old 15" monitor. If it was me, I would
be inclined to hang on till it dies and put the money towards a new TFT. See
what the other guys here say before you decide.
With best regards, 3T39. E-mail:

" bravely wrote to "All" (14 Jul 05 08:58:37)
--- on the heady topic of "CRT image shrinks and grows with changes to
brightness"

da From:
da Xref: aeinews sci.electronics.repair:53191

da I have a 7-year-old 15" CRT monitor that is connected to a standard
da PC. Lately I noticed that the size of the monitor's onscreen image is
da affected by changes to the image's brightness (the brighter the
da wider).
da For example, my Desktop background is dark. If I click to maximize a
da white window, the onscreen image expands by (approximately) 1mm on
da every border. If I then click to minimize the window, restoring the
da dark Desktop, the image contracts to its previous state. The same
da occurs when the monitor's Contrast control is quickly rotated from one
da end to the other.

da Is this behavior normal or a sign of a dirty or aged CRT? And speaking
da old CRTs, would it be wise, with respect to health or sight risks, to
da continue to use this monitor as long as it's operating properly (as
da the average user would say)?

Dave

It might be a B+ voltage regulation problem. However, a weak CRT could
also cause the picture size to change. Normally the HV tracks the
average beam current so that as a result the size stays the same (HV
derived vertical supply). But when CRT emission drops enough the
tracking is lost and this shows up as effects in pix size (both horz &
vert). Test the crt emission to be sure.

A*s*i*m*o*v

.... High voltage can give a dangerously uncomfortable discharge.

Considering that the tips are full (slight exageration) of 15" monitors, just
go a grab a new one if you don't want to spend cash

David

3T39 wrote:

Hello, !
You wrote on 14 Jul 2005 08:58:37 -0700:

da For example, my Desktop background is dark. If I click to maximize a
da white window, the onscreen image expands by (approximately) 1mm on
da every border. If I then click to minimize the window, restoring the
da dark Desktop, the image contracts to its previous state. The same
da occurs when the monitor's Contrast control is quickly rotated from one
da end to the other.

da Is this behavior normal or a sign of a dirty or aged CRT? And speaking
da old CRTs, would it be wise, with respect to health or sight risks, to
da continue to use this monitor as long as it's operating properly (as the
da average user would say)?

This symptom is a sign of faulty HT regulation. not the CRT. It can be
fixed, but I wouldn't bother with an old 15" monitor. If it was me, I would
be inclined to hang on till it dies and put the money towards a new TFT. See
what the other guys here say before you decide.
With best regards, 3T39. E-mail:

What monitors use beam current to regulate HV? Seems like a foolish idea to
me. Why should HV vary as a function of beam current? Who does this? I
don't work on many computer monitors, but I know of no TVs that work this
way.

Leonard

"Asimov" wrote in message
...
" bravely wrote to "All" (14 Jul 05 08:58:37)
--- on the heady topic of "CRT image shrinks and grows with changes to
brightness"

da From:
da Xref: aeinews sci.electronics.repair:53191

da I have a 7-year-old 15" CRT monitor that is connected to a standard
da PC. Lately I noticed that the size of the monitor's onscreen image is
da affected by changes to the image's brightness (the brighter the
da wider).
da For example, my Desktop background is dark. If I click to maximize a
da white window, the onscreen image expands by (approximately) 1mm on
da every border. If I then click to minimize the window, restoring the
da dark Desktop, the image contracts to its previous state. The same
da occurs when the monitor's Contrast control is quickly rotated from one
da end to the other.

da Is this behavior normal or a sign of a dirty or aged CRT? And speaking
da old CRTs, would it be wise, with respect to health or sight risks, to
da continue to use this monitor as long as it's operating properly (as
da the average user would say)?

Dave

It might be a B+ voltage regulation problem. However, a weak CRT could
also cause the picture size to change. Normally the HV tracks the
average beam current so that as a result the size stays the same (HV
derived vertical supply). But when CRT emission drops enough the
tracking is lost and this shows up as effects in pix size (both horz &
vert). Test the crt emission to be sure.

A*s*i*m*o*v

... High voltage can give a dangerously uncomfortable discharge.