CRT image shrinks and grows with changes to brightness

Hello, da_a snipped-for-privacy@yahoo.com! 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: snipped-for-privacy@hotmail.com

"da_a snipped-for-privacy@yahoo.com" 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_a snipped-for-privacy@yahoo.com 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

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