CRT Monitor Odd Behavior

I just set my monitor to 100hz, the setting I used to keep it at. With a mostly black picture the desktop streches beyond the edges of the screen and is dark and slightly purple. I guess I have some issue in the horizontal deflection circuitry. I'm a novice at PC monitors so any suggestions would be great.

No one needs a refresh rate that high. Set it to something reasonable (e.g. 75 or 85Hz) and see if that helps.

Large white images require more current.

Clearly the supply voltage for that part of the circuitry is sagging under the additional current demand. A PSU problem.

Graham

If it used to work and is within the specs of the monitor scan rate, then that's not the issue.

Something is failing in the deflection or power supply, and the regulation is suffering.

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Sam Goldwasser wrote in news: snipped-for-privacy@minus.seas.upenn.edu:

my guess would be electrolytic caps,bad ESR. You MUST use low-ESR,105degF caps for replacements.

Not a task I'd suggest for a neophyte,I suggest buying a new LCD monitor.

With the ageing of the monitor, the power supply regulation and scan circuit stability has decreased. The most common cause are electrolytic capacitors going high in ESR. If all the capacitors in the monitor were to be checked with an ESR meter, there is a possibility of finding many of them out of specs. This may not be a feasible repair for a monitor as old as the one that you have.

--

Jerry G.

Mike

Well it's not my first time working on a CRT, but I just don't have tons of expirence. I've fixed minor things in TV's before, cold solder joints, etc. I have an ESR meter so with a little time I should be able to find the suspect caps.

Well the interesting thing is that it appears to be doing the opposite. It is clear when a large white image is on screen, but blooms when the image is dark.

Mike

As old? It is from 2001 I don't really think it is that old. I have monitors way older than that.. I have an IBM VGA monitor from 1990 and a Tandy CGA from about 1986 that works great still.

It would be nice to get a smaller monitor on my desk, but money is an issue so I'll be re capping the monitor when I get time.

Interesting thing is that picture color, quality, brightness is all ok. Guess it is probably in the deflection section.

Indeed, it 'floors' me each time I read this sort of time-perception in posts; soon we will all have concepts of longevity appropriate for fruit-flies.

Anyway, one of our local universities recently put out hundreds of late-model monitors in hallways for giveaway since they had converted to lcd to save power campus-wide. Are you in an area with electronics recycling? Surely back alleys also are good sources for discarded monitors. I find good working ones nearly every day here in a smaller U.S. city, in all screen sizes ;-).

Regards,

Michael

While I won't claim to have anywhere near the experience that you have, what I have seen suggests that in many cases, it may infact be a single bad cap with high ESR that is the problem, especially if the monitor or TV had no obvious symptoms before.

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Well it depends on the part of the circuit the parts are in. Nothing in a monitor gets over 85C, but 105C caps will usually last longer. There's little reason not to buy them, but you can use what you have on hand and it will work in most cases.

Agreed on the first part, but the LCD monitor depends on whether he likes them, I much prefer the image on a good CRT and know plenty of others like me.

Look around the horizontal deflection and HV areas, really with an ESR meter it's pretty easy to test almost all of the lytics in the monitor, hardest part is getting to them, but the Viewsonics are not too bad to work on.

I replaced a pile of caps in a 14 year old 17" monitor a couple weeks ago, the image looks better now than it has in years. It's old tech, but my mom is still happy with it so I figured why replace it?

Absolutely agreed. Craigslist and Freecycle (google either one) list free, working monitors every single day. Thrift stores will hardly accept them...although they usually have a few for $25 or less. I put out a working 17" on the curb the other day, just because I have so many that I'm tripping over them. I finally had to toss it....

That said, I've got a 15" Sony composite sitting next to my desk as a 'repeater' for the home theater setup (hooked to a 'Video Sender' rf receiver). It must be 20 years old, but works great.

jak

Which reminds me that time flies like an arrow, but fruit flies like a banana.

start with the simplest: by changing the caps on the b+ line from the power supply to the horizontal/line stage.. typically rated 160 volts or more. don't bother measuring them, just replace. if no joy, then work back into the primary of the power supply.

chances are this monitor has a few years of life left in it , so don't give up and buy one of those 'orrid LCD things.

let us know how it goes.

-B.

Well I thought it was thermally sensitive since it worked fine until the monitor heated up... Now it appears to work fine for the time being. I'm sure that I will have to fix it at some point, but right now it is not showing any symptoms. I guess I'll have to wait for it to act up again.

Mike