View Full Version : Raster Rotation


lnx64
02-14-2013, 04:06 PM
Not exactly a TV, but close enough. The raster on my old IBM computers monochrome CRT, is slightly rotated.

Do I just simply rotate the yoke to fix this?

http://img.photobucket.com/albums/v395/Evilweredragon/IMG_1830_zps9b310c6e.jpg

Also, if you look at the line at the bottom of the screen, it's not straight either, kind of like it bows slightly.

walterbeers
02-14-2013, 04:44 PM
Yes, rotating the yoke will rotate the image, however it won't do anything for the bowing. Maybe there is some kind of pincushing controls, but on one that old I doubt it. Tilted picture was also a very common problem with TVs as well. I don't know why, but somehow they seemed to rotate themselves, probablly from the heat inside the monitor or set.

lnx64
02-14-2013, 10:31 PM
Crap, the yoke is GLUED in place.

I don't think I'm going to be able to fix this rotation without breaking the tube.

Geoff Bourquin
02-14-2013, 10:59 PM
Some monitors have a rotate option in the menu. Also, there could be something nearby that is magnatized causing the rotation. Maybe a pot someplace.

lnx64
02-15-2013, 08:44 AM
This monitor is built into the computer, and it's from the 80's, it has no menu. The monitor is a dumb fixed frequency monitor that only knows 31KHz 60Hz 480 line (or 70Hz 400 line).

I thought it was magnetism but I've tried all sorts of locations in the house, same slight rotation.

crtfool
02-15-2013, 09:36 AM
Are you sure that this is a new problem? Maybe you just never really noticed it before. It is unlikely that a monitor this old with a cemented yoke could just shift the raster rotation. The slight pincushioning may be adjustable, but I would not attempt it.

I am a bit of a fanatic when it comes to geometry issues, but your monitor looks great to me - the crosshatch is nearly perfect, as far as I am concerned - this would not bother me at all.

andy
02-15-2013, 10:37 AM
...

lnx64
02-15-2013, 11:42 AM
It's definitely glued. I loosened the clamps and it won't budge. It looks like hot glue was placed all around the yoke.. I could probably try and scrape it off but I'd likely damage the CRT.

I don't know if this is a new thing or not. I only noticed it now to be honest.

I have an old picture of me from when I was a little kid, standing in front of this computer when it was in DOS Shell (all white background). I'll need to see if it looked rotated then too.

old_tv_nut
02-15-2013, 10:37 PM
Looks to me like it's original. You could look to see if there are permanent magnets for geometry correction - if not, it is what it is.

lnx64
02-15-2013, 11:04 PM
Ok, I'll check for magnets, didn't see anything though. If anything I'll just leave it. rotation is my biggest pet peeve.

holmesuser01
02-16-2013, 12:04 PM
I've seen worse on monitors that people are using today.

I'd leave that one alone, too.

Geoff Bourquin
02-16-2013, 03:34 PM
What about rotating the whole CRT? Maybe the screws (or bolts) on the corner ears are a tad loose and allowed the whole tube to move.

Eric H
02-16-2013, 03:56 PM
Fixed it in Photoshop for you, seems to be about .2 degrees off.

Tilt bugs me too, the yoke should be able to rotate, how about a shot of the yoke so we can see what's holding it. Hot Glue is pretty easy to remove, if it Epoxy then not so much. Geometry on a CRT is never going to be perfect, even with pincushion controls they are usually a bit bent.

Maybe if you sat a Magnet on the top left corner it would pull the beam up?

lnx64
02-16-2013, 04:15 PM
I don't personally have an internal pic since I had buttoned the computer back up, but one of my friends has the same model and an internal pic from his, and his yoke is glued the say way.

http://kishy.dyndns.org/?attachment_id=419

old_tv_nut
02-16-2013, 04:36 PM
What are these?

lnx64
02-16-2013, 04:47 PM
No idea, they look like washers to me, but I didn't notice that on mine.

old_tv_nut
02-16-2013, 10:20 PM
No idea, they look like washers to me, but I didn't notice that on mine.

Seems like a very strange place for washers - I'm thinking they could be magnets, or at least metal pieces, used to adjust the scanning fields, and then glued in position.

lnx64
02-17-2013, 12:24 AM
Hmm, I'll need to double check this. Mine definitely didn't have anything there on the yoke like that. Perhaps it used to and it fell off.