HD CRT TV drooping in one corner after being dropped. Fix?

[BazookaBen]

So my buddy has a really nice Sony Super Fine Pitch CRT, and last time he moved, he droped it on a corner and now the geometry is a little messed up in that corner.

We haven't opened it up, but I'm guessing one of the internal magnets fell off. Have any of you seen something like this happen before. Any ideas on if it could be the magnets or something else?

[lolitsevan]

I had ups annihilate a pvm that i ordered last year, and it ended up causing distortion on the right side of the screen, making it green, and the top right corner was totally warped. I learned that this meant the shadowmask was likely shifted, which is unfixable, because the shadowmask is sealed in the tube. Eventually the pvm's input selector gave out all together, but for a while I was able to use some reasonably strong magnets on the right side of the screen to move the shadowmask around, and it would kinda of 'snap' into almost the correct position with the right caressing (lol). Of course this goes away when you turn the display off, so youll need to do this every time you turn it on. I was really careful with the magnets at first but it took a pretty decent magnet to get through the shielding/case on the outside of the tube to manipulate the shadowmask.

All this to say, without seeing pictures, my guess is the shadowmask shifted, and now youll need to play with magnets to get it right probably, and likely youll need to do this anytime you use the tv. Also, fwiw, I tried playing with the small magnets on the yolk to get finer manipulation but that didnt seem to do anything, the only thing that impacted my issue was using half of an old microwave magnet and rubbing it over the affected area until it looked how it should(direction matters, sometimes it gets worse before it gets better, etc). Underscan was also helpful in eliminating some of the screen where the shadowmask had shifted, but I hated not using all of my tv.

[BazookaBen]

Ouch, that's bad news. Was hoping there would be a more permanent fix.

I didn't realize the shadow mask was a physical object, I thought it was just a method for applying phosphors to the glass.

[lolitsevan]

I could be wrong, but I'm pretty sure its a metal layer sealed inside the tube just behind the screen itself that directs the signals from the electron guns to make the image. Anything I learned about this stuff I pieced together when I was trying to troubleshoot my own. Yeah, I wish I had better news, but I actually went to a local tv repair place that's been operating a while and picked some of the older tech's brains about crt repair and maintenance and thats what we came up with.

Technically the tv youre talking about might have an 'aperture grill' instead, but from what I learned its acting the same and would respond similarly to the 'magnet treatment'.

[BazookaBen]

Thanks for the info. What sort of magnet were you using? A large refrigerator magnet or something stronger?

[Ed Oscuro]

I didn't realize the shadow mask was a physical object

It is, but it's also something not found in Sony sets, so it's the wrong term. Aperture grille refers to the wires in Sony sets; a shadow mask is a metal plate with holes punched out. Both have the same purpose, but Sony's was more efficient.

If the aperture grille wires are damaged or no longer anchored (you can test this by tapping the side) you'll see a shimmering effect, or you'll see color purity issues. Doesn't sound like that's happening here.

It could be a magnet, but maybe the yoke is out of position.

[Endymion]

http://media-2.web.britannica.com/eb-me ... A427B6.jpg

[BazookaBen]

Thanks for the info Endymion/Ed.

but maybe the yoke is out of position.

Is that something that can be repositioned? In the diagram above it seems to be outside the tube so maybe it is accessible?

[Ed Oscuro]

Yeah, you'd have to look up your model to find out where the controls are.
http://www.repairfaq.org/samnew/tvfaq/tvcrtcona.htm gives some overview of this, though the details might be different.

But don't mistake my thoughts for a diagnosis. Without actually knowing what the problem is you can make things worse. My mention of tapping the side wasn't just a suggestion, but something that you can try (in the absence of ability to test / recognize problems in a more systematic fashion).

[BazookaBen]

Thanks, that link is pretty helpful. If the problem is the yoke, it seems like I would be adjusting the bottom left side (corresponding to the area of the screen that is drooping), maybe checking if a bracket or screw popped off.

But the first thing I'm going to do is check if there are any loose magnets that fell off the tube. If there's no evidence of misplaced magnets, then I'll give it a tap to see if there's any shimmering. If no shimmering, I guess from there I can look at the yoke and other potential problem areas.

[Xan]

I believe adjusting the yoke can mess up convergence and purity a lot so it's something to be careful with.