So I recapped this unit over a month ago, and it looked pretty good geometry wise. Then all of a sudden I started getting pincushion at the bottom, and a slight overscan on the top left. I’ve tried adjusting the magnetics on the yoke, didn’t affect it. I checked the values of all the new caps and they’re all in range still. I looked for broken solder joints, found nothing. I checked the resistor at r2 that everyone says causes geometry issues. Still reading 150ohms. I included pics with several different adjustments. The problem persists. I tried manual degaussing as well. I sent the overscan pic to more clearly show the problem, but it shows in range as well but not as well in a photo. Anyone have any ideas? I really wanna get this one back in the working category. Thx
Anonymous
User login
Please support the defense of Ukraine.
Direct or via Unclutter App
Active forum topics
Recent content
Navigation
No Ads.
No Trackers.
No Social Media.
All Content Locally Hosted.
Built on Free Software.
We have complied with zero government requests for information.
Degaussing a black and white tube is pointless because there is nothing in the face of the tube that can be magnetized.
Your pictures don't show pincushion distortion (left and right raster edges bowing in or out), but keystone distortion (bottom of raster wider or narrower than top). If this happened suddenly, it could point to a shorted turn in the yoke. The way to diagnose a shorted turn is with a "ringer" such as the Anatek Blue Ring, but there is an alternative method described in Sam Goldwasser's invaluable guide. It involves swapping the two wires going to the vertical coil in the yoke (pins 1 and 2 in J1), therefore scanning the picture bottom-to-top instead of top-to-bottom. If the bottom of the raster is still narrower than the top, then the horizontal coil in the yoke must have a shorted turn.
IMG_7167.jpeg
IMG_7168.jpeg
Rotate the Yoke 180 degrees. Easy Peasy
That's what I was afraid of. When you reversed the pins to the vertical yoke, the whole raster is scanned from bottom to top; as far as the electronics on the analog board know, the bottom is now the top and the top is now the bottom. So a problem stemming from an electronic component would have flipped vertically.
Since the keystone is the same as before (narrower at the physical bottom of the raster) it can't be caused by any of the electronics: the only remaining causes must be in the yoke or the centering magnets. One possibility is a shorted turn in the horizontal yoke coil.
The horizontal coil produces the magnetic field that deflects the electron beam left and right. In the proximity of a shorted turn, the magnetic field is weaker because that turn isn't doing any work. So where the keystone is narrow is near the shorted turn. The resistance of the whole horizontal coil should be 0.2 Ω; you might be able to detect a slightly lower resistance with a sufficiently accurate ohmmeter.
It looks like you need a yoke.
Think I'll just pick up another donor unit and swap the guts.
Ok I changed the yoke and the problems have gone away. Tyvm everyone.
IMG_7281.jpeg