CRT question

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CRT question

Hi all. So I found an old 17" Cybervision VGA CRT in my parents crawl space - it's been there many years obviously a damp space. It looks to be in good shape / the VGA connector screws did have rust though - I think I could clean it up with some contact cleaner. I plugged it in, turned it on and the screen showed no signal messsge BUT there was some crackling / ticking  noises which eventually stop. I did this several times and it seemed to happen less but still hear some. My question:  do you think it's safe to use and is it safe to use with my original Apple IIe Enhanced which has a AllVGAS  VGA scaler card in it (currently connected to an ASUS LCD). I don't want to burn my house down or fry my Apple IIe. Opinions? Thanks!

m0ebiu5

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Probably yes, but it wouldn’t

Probably it's perfectly safe, but it wouldn’t hurt to open it and inspect it for damage and possibly determine where the noise is coming from. From I remember some of these multi-sync monitors used relays for the different frequencies, so it might be just them. The degaussing coil also used a relay in those days.

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Looking through the tiny vent

Looking through the tiny vent holes in the top with a flashlight it looks very clean. I'm hesitant to open it up because of the inherent danger of the tube etc. Thank you CVT.

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The crackling noises you

The crackling noises you describe sound more like high voltage discharges, especially since they sound different each time you turn it on and gradually go away. If the picture jumps, dims, or collapses during these noises then that would be a dead giveaway. Probably nothing to worry about if they eventually stop altogether. Most likely just some dust that collected over the years and is slowly being zapped away.

If it continues, you might want to investigate further. You could remove the back, darken the room, and then from a safe distance power up the monitor. If you see flashes that accompany the "zap" then you'll see where it is coming from. Just blowing the dust away might be enough. If there is a consistent area where an arcover is occuring you might need to insulate it with some glyptol or nail polish. Just wait long enough for the CRT to discharge before getting that close.

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Thank you Jeff - I'm going to

Thank you Jeff - I'm going to clean the vga connector, give it a few days to sit in regular humidity and try connecting it to something. Just wanted to make sure it was safe to do so.

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So I tried the monitor with

So I tried the monitor with my Apple IIe - it turned on with no noise this time and the picture was great but I'm getting a ticking noise with a picture flicker at random intervals. I'm hoping maybe it's just not dried out enough or that it will go away with a few more days in the house. I have unplugged it for now. Any thoughts?

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EHT

The random "ticking" with picture flickering sounds like a EHT arc-over or discharge, as jeffmazur said above.

Sometimes this happens because the rubber jacket on the anode cable developed a crack. It can be fixed by (carefully, lightly) cleaning the cable and using a high voltage varnish to cover up the crack. I've used a product called "MG Chemicals Super Corona Dope 4226".

However, and I don't mean to cause undue worry, there is another worse possibility, which is that the flyback transformer (also called the LOPT) has developed a crack internally and that is where the discharge is happening. Obviously if the arc-over path is internal to the LOPT, it can't be fixed with varnish. You would be able to tell the location by doing as jeffmazur suggested and running the set in a dark room after removing the back cover.

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m0ebiu5 wrote:So I tried the
m0ebiu5 wrote:

So I tried the monitor with my Apple IIe - it turned on with no noise this time and the picture was great but I'm getting a ticking noise with a picture flicker at random intervals. I'm hoping maybe it's just not dried out enough or that it will go away with a few more days in the house. I have unplugged it for now. Any thoughts?

 

This monitor has convection air cooling, so you can be sure that it's fully dry after running it for about 15 minutes. There is no need to wait a few days, it's not going to make a difference in how dry it is.

 

High voltage discharge sounds exactly like the sound you get when you run you fingers over the front glass of a CRT TV after it has been running for a while. Do you hear that?

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I haven't run the monitor for

I haven't run the monitor for 15 min yet since I pulled it out of  their crawl space. Sound wise the only thing I heard was the random ticking sporadically with screen bounce when the tick happens. I will run it longer to see if it goes away when I get home tonight and get back to you guys. 

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repair guide

This is the best all-around guide to CRT repairs that I know of: http://www.repairfaq.org/sam/monfaq.htm

In particular, check:

Testing of flyback (LOPT) transformers

Snaps, crackles, and other HV breakdown

 

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That's a great resource.

That's a great resource. Thank you! So tonight I have been using the CRT quite a lot and the ticking seems to have gone away - there was some at first and it became less and less. I haven't heard it now for a few hours I believe. Crossing my fingers and knocking on wood!

 

 

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