PVM 14-L2 Broken apeture grille? Purity issue spot

[pigswill]

Hi, I was hoping some CRT experts might be able to help me. I've had this PVM for awhile but haven't really used it much for 240p content until recently and I noticed a discoloration spot at the top of the screen.

Spoiler

It might be hard to see, the spot is in the black box. I'm using only the green because it makes it easier to see.

The internal degauss on the PVM seems to work, it makes a thunk noise and the colors get all screwy, but doesn't fix the problem. I don't have a degaussing coil to try.
I opened up the case to see if a magnet that was supposed to be stuck to the tube had fallen off, but didn't see anything.

I've noticed tapping the case lightly on the sides and top seems to make the colors in the top left flash/change for a split second then return to normal. I also tried to tilt it some like this:

Tilting it to the right made the problem much worse until I sat it back down, tilting it to the left didn't seem to make it worse though.

The last thing I tried was i got a slightly stronger fridge magnet and moved it around the outside of the case. It just made the spot in the picture bluer so I stopped for fear of making it worse.

I don't know much about this stuff, could it be a damaged aperture grille ? Or could it be fixable with something like a stronger degauss or magnets directly on the tube? Thanks for any help.

[Josh128]

Honestly, to me, it doesn't look like a damaged aperture grille. Have you recently moved the position of the CRT as in rotating the face of it some difference of N, S, E, W vs where its been for a while? A lot of times you will see a purity issue like this after moving the set. You tilting the CRT could easily cause purity issues due to position in relation to earths magnetic fields.

Try this--put up a screen where you can see the issue clearly, then rotate the CRT about 25 degrees in a given NSEW direction. Check to see if the issue has gotten better or worse. Rotate another 25 degrees, rinse and repeat. Iits very likely you will find a position where the issue disappears and/or moves to another spot on the CRT. This would be confirmation that your AG is OK and the set is just gaussed or as you suspected, a purity magnet has fallen off or moved.

Another test you can do is to power up the set from cold and put up a full white screen. Note the location and intensity of the issue. Let the set sit with the white screen for 10 minutes or so, and note if the issue has moved or gotten worse. If it does, then its likely your AG has an issue and is susceptible to stretching/warping as it heats up. I think that is more common with solid screen shadow mask sets vs aperture grilles, but it could happen.

Report back please!

[Dochartaigh]

Easiest possible fix is to buy a small neodymium magnet (think mine are 6x2mm), open the case, and try to see if there's a spot around that area you can place the magnet that will make it go away. I've had numerous issues like this and nearly all were fixed about 95% of the way so they're practically invisible on any color background.

Older sets sometimes had a magnet in a holder you could rotate to help with this but I've never seen one in a newer PVM so it's unlikely one fell off. Convergence strips might help but usually not in a case like this. Adjusting the yoke is something else people try, but I find that to be a bit more difficult. Could also just be permanent damage to the AG.

[Guspaz]

I had the exact same issue with my 14L2 (albeit on a different corner), ablue discolouration. If you look at the tube you'll note that there are already four disc magnets glued to the tube on each corner, I found that putting additional magnets on top of or near the factory-installed magnets resolved the issue. I wouldn't use something crazy strong like a neodymium magnet, I just used magnetic tape so that I could stack it to adjust the strength, and that was sufficient.

These are the magnets that I tried, purchased at a local art store:



Fixing the issue required (stacked) six of the small discs, or two of the large discs, or three layers of 1.5" of magnetic tape. In the end, my final solution was the magnetic tape, because it was the thinnest stack height. I installed them thusly:



The little roll of duct-tape underneath was because the adhesive on the magnetic tape is on the wrong side to stick to the tube: the magnets only fix the issue if they are facing in the direction with their adhesive side upwards. I then secured it with duct tape like this:



That was 6 years ago and it's been fixed ever since, haven't opened it up since then.

[pigswill]

Thank you for the responses!

Honestly, to me, it doesn't look like a damaged aperture grille. Have you recently moved the position of the CRT as in rotating the face of it some difference of N, S, E, W vs where its been for a while? A lot of times you will see a purity issue like this after moving the set. You tilting the CRT could easily cause purity issues due to position in relation to earths magnetic fields.

Try this--put up a screen where you can see the issue clearly, then rotate the CRT about 25 degrees in a given NSEW direction. Check to see if the issue has gotten better or worse. Rotate another 25 degrees, rinse and repeat. Iits very likely you will find a position where the issue disappears and/or moves to another spot on the CRT. This would be confirmation that your AG is OK and the set is just gaussed or as you suspected, a purity magnet has fallen off or moved.

I did what you said and rotated it around 60 degrees, according to this compass, and the problem seems to be gone! Or if its not gone its got much better or moved somewhere else that I'm not noticing. Strangely The monitor has been sitting in the same spot for well over a year I haven't recently moved it or anything.

If I put it back into the original position and used a degaussing coil/wand would that remove the issue? I've also heard about putting 2 pvms face to face and using one to degauss another, I have a 20 inch one I could use, would that work?

Another test you can do is to power up the set from cold and put up a full white screen. Note the location and intensity of the issue. Let the set sit with the white screen for 10 minutes or so, and note if the issue has moved or gotten worse. If it does, then its likely your AG has an issue and is susceptible to stretching/warping as it heats up. I think that is more common with solid screen shadow mask sets vs aperture grilles, but it could happen.

Report back please!

I actually do have an issue when a white screen is displayed for a long time, but in the opposite corner. It will discolor the right corner and after I switch it off the white screen to something else it will slowly return to normal.

[pigswill]

I had the exact same issue with my 14L2 (albeit on a different corner), ablue discolouration. If you look at the tube you'll note that there are already four disc magnets glued to the tube on each corner, I found that putting additional magnets on top of or near the factory-installed magnets resolved the issue. I wouldn't use something crazy strong like a neodymium magnet, I just used magnetic tape so that I could stack it to adjust the strength, and that was sufficient.

These are the magnets that I tried, purchased at a local art store:

Spoiler

Fixing the issue required (stacked) six of the small discs, or two of the large discs, or three layers of 1.5" of magnetic tape. In the end, my final solution was the magnetic tape, because it was the thinnest stack height. I installed them thusly:

Spoiler

The little roll of duct-tape underneath was because the adhesive on the magnetic tape is on the wrong side to stick to the tube: the magnets only fix the issue if they are facing in the direction with their adhesive side upwards. I then secured it with duct tape like this:

Spoiler

That was 6 years ago and it's been fixed ever since, haven't opened it up since then.

Cool, that seems like an easy fix. I'll have to buy some magnetic tape like that if the issue isn't fixable with degaussing or if another monitor has issues. Thanks for the pictures too they are very helpful.

[Josh128]

Thank you for the responses!

Honestly, to me, it doesn't look like a damaged aperture grille. Have you recently moved the position of the CRT as in rotating the face of it some difference of N, S, E, W vs where its been for a while? A lot of times you will see a purity issue like this after moving the set. You tilting the CRT could easily cause purity issues due to position in relation to earths magnetic fields.

Try this--put up a screen where you can see the issue clearly, then rotate the CRT about 25 degrees in a given NSEW direction. Check to see if the issue has gotten better or worse. Rotate another 25 degrees, rinse and repeat. Iits very likely you will find a position where the issue disappears and/or moves to another spot on the CRT. This would be confirmation that your AG is OK and the set is just gaussed or as you suspected, a purity magnet has fallen off or moved.

I did what you said and rotated it around 60 degrees, according to this compass, and the problem seems to be gone! Or if its not gone its got much better or moved somewhere else that I'm not noticing. Strangely The monitor has been sitting in the same spot for well over a year I haven't recently moved it or anything.

If I put it back into the original position and used a degaussing coil/wand would that remove the issue? I've also heard about putting 2 pvms face to face and using one to degauss another, I have a 20 inch one I could use, would that work?

Very good. At least now you know its not your AG. You can try some additional strategically placed magnets on the back or edges of the tube, but before you do, give the set a few days/week or so of normal use (make it a point to use it at least once per day for at least 10 minutes or so) and see if it doesnt clear up on its own from regular degaussing when turning on. Ive had sets do this and after a few days or so the issue resolved itself.

As far as the PVMs facing each other thats an idea, but I have no clue as to how effective it would be. You could give it a shot.

About the pure white screen, some very minor purity blooming as things heat up is not uncommon. If theres a real issue, you'll know it and magnets will do nothing to fix it. Check the video below of a Wei-ya M-3129 I purchased that had an apparently detached/partially detached mask. Whats obvious is that a switch to a black screen for a while "fixes" the problem for a bit, then a switch back to a white screen shows it quickly returning. To see the dramatic change, go to 3:00 in the video after I switch back to white from a cool down and you can see the terrible baby-poo green begin to engulf both sides of the screen.

https://www.youtube.com/watch?v=5l7eEcJTqcc

[Guspaz]

When I was originally diagnosing this issue, I bought a degausing coil. Like, a proper one, which draws enough power that it's uncomfortable to hold in your hand because it vibrates a lot and gets quite warm. It didn't help in the slightest. That doesn't mean it won't help you, but I wouldn't count on it either.

[pigswill]

Just wanted to post an update to this.
I did what you suggested Guspaz and went ahead and opened it up and attached a few magnetic tape strips to the tube. This is my first time doing this kind of adjustment so it's not perfect, but it is looking much better! Thank you guys for the help, really appreciate it.

[Guspaz]

Play around with the number of stacked strips of tape (stacked on top of each other) and their position/orientation, hopefully you can dial it in. I was able to get mine completely eliminated to the naked eye, though it still shows up very faintly on a camera. A solid red background (like from the 240p test suite) is useful for this since it's most visible on that background. So you can experiment and move it around and see how the screen reacts in real-time.

[Josh128]

Awesome! Always good to see a CRT repair success story.