Trying to repair a 4" Horizontal CRT monitor.

[Retroplayer]

I have a project in mind that called for a flat CRT monitor and found just what I was looking for in an old video intercom system (Well, first I bought and modified a Zenith BT-044S before finding out about these intercom systems).

I have it working pretty well, except that the display is twisted a bit and shifted to the right. Also the size is off a bit. I tried to carefully adjust the unlabeled pots on the board, but nothing is affecting position. I got the size mostly dialed in now, though.

I can use a magnet placed strategically to untwist the display, but still nothing on the offset of the screen. The magnet is also making the text size vary across the screen (they scrunch more and more toward the right side) so, I am not happy with that solution.

Would loosening the yoke and adjusting it be the right trick or do you think some components my be the issue like aged caps?

Any help or advice would be appreciated.

This is what I am looking at (no magnets being used here) :

Both the BT-044S and this monitor seem to be doing the same thing. I have tried different video sources. I am wondering if it might be the nature of this type of screen or the very close proximity to the flyback transformer. Just looking for tips on where to start to figure out how to correct it.

[MadMan]

Using a magnet might gauss the screen and make it worse. Of course it can be degaussed, but that's a process. I would say that turning the yoke a bit would correct this, but if you note that the left side of the numbers is a near-perfect vertical line, for whatever reason, the image is being skewed up on the right side. If you tried two different monitors and two different video sources, perhaps something else is amiss, like bad cables or interference. Try the video source on a known-good tv or monitor.

[jr_tech]

I agree that turning the yoke should help, but don’t expect perfect geometry:

http://www.videokarma.org/showpost.p...51&postcount=1

Since there is no shadow mask, the screen will not get magnetized.

jr

More geometry pix here:

http://www.videokarma.org/showpost.p...2&postcount=90

jr

[Retroplayer]

Originally Posted by MadMan

Using a magnet might gauss the screen and make it worse. Of course it can be degaussed, but that's a process. I would say that turning the yoke a bit would correct this, but if you note that the left side of the numbers is a near-perfect vertical line, for whatever reason, the image is being skewed up on the right side. If you tried two different monitors and two different video sources, perhaps something else is amiss, like bad cables or interference. Try the video source on a known-good tv or monitor.

I have seriously considered that it must be getting pulled from somewhere else. I notice that these are very sensitive to static. When I put my fingers near the glass, the image moves almost like a plasma globe. Maybe some better shielding and more ground points would help.

One common thing on both displays is that the flyback transformer is right next to the neck on the left side (the side being pushed away).

Using the magnets in the right polarity, when I pull down the right top, it squares up perfectly (the magnets are near the yoke, not the glass.) I found with a magnetized screwdriver that there is a sweet spot on the yoke that if I rest the driver there, the image is nearly perfect geometry. It is down near the circuit board right about where the deflection IC is located.

I am going to try my experiment in some different locations in the house.

I have tried my video source (it's an Arduino with the TVOut library) on a 3" color LCD monitor and a Sony FD-10A and it seems to work fine on those. In the new fangled world, it would almost seem like the phase is off. But no such adjustment on these old sets.

I'll try manipulating the yoke and different locations. At least it is just a B&W set, so not much danger completely bodging the yoke alignment. Just need to be careful not to get myself zapped working in such a tight location. Thanks!

[Retroplayer]

I ended up finding your threads after I posted last night and found them very interesting and helpful. My plan is to make an animated face for an old 80's robot, so perfect geometry is not required. I just need the image to show up in a predictable spot and be able to fill up nearly the whole screen. I will also be displaying some text/gui occasionally, so I want that to be somewhat square.

EDIT: So, no risk of gaussing, then? If I can get a magnet to give me perfect geometry, perhaps that is the best way to go.

Originally Posted by jr_tech

I agree that turning the yoke should help, but don’t expect perfect geometry:

http://www.videokarma.org/showpost.p...51&postcount=1

Since there is no shadow mask, the screen will not get magnetized.

jr

More geometry pix here:

http://www.videokarma.org/showpost.p...2&postcount=90

jr

[zeno]

Geometry was a common problem on the Sony & Sony built Zenith.
Usually a key stoned pix. Bad news is we never fixed them, just
brought the to the Zenith distributor in Boston for repair. I would
guess its a SMD electrolytic cap. Got steady hands ? I dont......

73 Zeno
LFOD !

[Retroplayer]

I think I achieved an acceptable result by manipulating the yoke and then re-adjusting the pots.

I really wanted to move the image down some more and then scale it up with the v-size and h-size pots, but apparently moving the yoke further away from the screen appears to work the opposite of what I expected (yoke further away pushes image up higher.) And I can't physically get the yoke any closer to the screen than this.

I think I am good for now.

Still open to any tips to improve it.

[Retroplayer]

The chip used in this monitor is CD1379CP for those that are interested.

https://pdf1.alldatasheet.com/datash.../CD1379CP.html

Not a bad monitor for about $9 shipped on ebay. Happened to be searching just the right terms at just the right time. There was no brand info on the doorbell, so I couldn't tell you a model to search for. It is not an Aiphone. Removing it from the door intercom base was simple and the display is a module with just a few wires going to the mainboard that were labeled even.

Now I am playing around with filters to put on the glass to color it red or green for effect and more sharpness. I will probably have to modify it to increase the brightness a little more.

[centralradio]

I remember these system from the 1980's.Glad that you dialed everything in and got it working Retroplayer...

Have a couple of those lollipop style tube Sony Watchman sets here...

[kf4rca]

Iconoscopes once used the offset gun design but it didn't last. Probably due to geometric distortion too.
FWIW I've got a manual for the Sylvania version of this set.

[kf4rca]

Its a Magnavox Escort 4 which was made by NAP who also made Sylvania.
According to my manual there is a pot labeled "keystone" which is to correct for geometric distortion.

[old_tv_nut]

Originally Posted by kf4rca

Iconoscopes once used the offset gun design but it didn't last. Probably due to geometric distortion too.
FWIW I've got a manual for the Sylvania version of this set.

The iconcoscope had to scan the image side of the mosaic target because the signal was taken capacitively from an opaque metal film on the back of the insulating target. The exception was a straight ultra miniature 2-inch diameter iconoscope, type 5527. I don't know the construction for sure, but I'm guessing it used a transparent or semi-transparent conductive coating so the light could enter through the back of the mosaic support (opposite side of the electron gun). This tube had even worse sensitivity than the studio iconoscopes (which were replaced by the much more sensitive image orthicon over a period of years after WWII).

Hams experimented with the 5527 in the late 1940s and early 1950s until Vidicons became common.

[kf4rca]

Anotherl problem with any kind of offset gun configuration would be focus. You couldn't get focus at the top of scan and focus at the bottom of scan, at the same time.
You could correct for keystoning pretty easily.
Retroplayer, let me know if you need any more scans.
There are some Escort 4's on Ebay, various prices:
https://www.ebay.com/sch/i.html?_fro..._odkw=escort+4