No convergence/purity rings w/ a bonded yoke. How to adjust?

[BazookaBen]

Has anybody dealt with this before?

I have the Sharp 27c540.

Spoiler

Service manual doesn't have anything for convergence adjustments: https://elektrotanya.com/sharp_27c540_c ... nload.html

I don't know how/if these guys are supposed to be adjusted. Could I add the convergence ring assembly from the neck of another CRT?

[Josh128]

Wow, thats strange. Maybe convergence strips only? If you could add rings from a yoke with similar resistance perhaps that would work but man that seems like it would be quite a project. Good luck.

[Ryoandr]

Some tubes have no rings and are factory set with permagnets

Philips tubes are like that.

[BazookaBen]

Do you know where they put these magnets? Like are they inside the yoke? Maybe inside that grey section of plates right behind the yoke?

[SuperSpongo]

I have a similar problem on a Barco. It could really use a slight yoke twist, but unfortunately the yoke is permanently connected to the tube.
Is it not supposed to be adjustable?

[buttersoft]

I think bonded yoke = non-adjustable. Set at the factory, and that's that.

[BazookaBen]

So a guy on reddit knows a few things about this and provided a couple patent documents that explain it in depth.:

https://www.reddit.com/r/crtgaming/comm ... &context=3

So that part under the sticker is the magnet. It's magnetized by a machine at the factory for each individual tube, speeding up the whole convergence and purity adjustment step.

I could definitely dial it in better if it had convergence rings to adjust, though. I may use the rings I salvaged off my older Panasonic tube and see if they work well enough if I put them immediately behind the magnet pictured.

OR I could find some very, very, small magnets and put them directly on the factory tuned magnet. But I would seriously need magnets only a few millimeters in diameter to avoid completely throwing everything off.

[SuperSpongo]

I love that guy on reddit! He's an old TV technician from Italy and really knows his stuff. He also calls people on their bullshit when they auto-recommend a full recap on every little thing.

[BazookaBen]

OK that makes a lot of sense. Was not expecting somebody to pull out patents from 1984

[buttersoft]

I wonder how the plastoferrite sleeve was magnetised in the first place? By an Extremely strong field? I should probably read the patent doc...

I like the idea of using very small external magnets on it, but I'd start with flat fridge magnets as those are about as weak as you can get.

[tongshadow]

Alright, so main takeaway is stay away from Philips and Sharp sets.

[matt]

Alright, so main takeaway is stay away from Philips and Sharp sets.

No, TVs with bonded yokes are fine as long as the convergence is good and the picture is reasonably level. Also, both of those manufacturers did use tubes with traditional convergence rings also. Come to think of it, I've picked up quite a lot of Sharp TVs and haven't seen a bonded yoke on one yet.

The very popular JVC D-series TVs often use bonded yoke tubes, but this doesn't seem to stop people from using them. The 27" Thompson tubes have an especially nice picture.

[Ryoandr]

Flatglass philips are bad

Videocolor/TTD tubes look fantastic, they were in arcade cabs and tvs from the Thomson group, though at some point they switched back to more traditional ring-adjusted.

[BazookaBen]

The 27" Thompson tubes have an especially nice picture.

My Sharp actually uses a 27" Thomson tube! https://i.imgur.com/IdVQX9Y.jpg You can see the sticker on the bottom.

And you're right, bonded yoke doesn't mean the picture is bad at all, it's actually quite good. I was surprised at how good the picture is after I made some tweaks in the service menu. Especially after disabling velocity scan modulation.

The only issue, for me, is that the bonded yoke and cylinder convergence magnet don't let me tweak things further. The bonded yoke and convergence magnet were used to speed up the manufacturing process, but of course I would be able to make convergence even better since I can spend two hours playing with a yoke and magnets, as opposed to the 60 seconds or whatever they gave it in the factory.

I was actually able to put some 6 pole and 4 pole magnets from another TV behind the cylinder magnet, and I did get center convergence better, but is isn't working exactly as planned. Like it doesn't seem the 6 pole magnets have any effect at all, so I was only really moving red and blue with the 4 pole magnet, which was helpful. I decided not to put any type of magnets directly on the sleeve because I don't know if I could change the magnetic field of it by messing with it too much.

But now convergence on the sides is off more than before, and I don't know if it's from having the rings behind the sleeve magnet, or maybe it now needs a yoke tilt. I'm also wondering if I should just remove the sleeve entirely, so I can completely replace it with the rings. But I also noticed there is some copper wires under it, the same type that the yoke is wound with, so I'm wondering what those do and if I'd screw things up much worse.

And attempting to remove the glue under the yoke sounds risky, if I wanted to adjust that. I've read the same people have damaged yokes attempting this, though others did it successfully. Since it's very hard to know if you've loosened the glue enough with, say, a heatgun, I could see a problem occurning where some glue somehwere on the tube is stil bonded and takes some wires with it or something.

And in the picture I posted above, I drew an arrow pointed at a rubber cap. There's an identical one on the right side. I'm curious if you guys know what might be under those. Because when I put a magnet on that, it alters convergence. but usually by way too much

[MKL]

But I also noticed there is some copper wires under it, the same type that the yoke is wound with, so I'm wondering what those do and if I'd screw things up much worse.

It must be the scan velocity modulation coil. You can disconnect it from the neckboard if you prefer the picture without it.

BTW, can you adjust horizontal size, parabola and trapezium? The manual is contradictory as it says they're adjustable but the schematics show there is no EW circuit.

[Josh128]

The 27" Thompson tubes have an especially nice picture.

My Sharp actually uses a 27" Thomson tube! https://i.imgur.com/IdVQX9Y.jpg You can see the sticker on the bottom.

And you're right, bonded yoke doesn't mean the picture is bad at all, it's actually quite good. I was surprised at how good the picture is after I made some tweaks in the service menu. Especially after disabling velocity scan modulation.

The only issue, for me, is that the bonded yoke and cylinder convergence magnet don't let me tweak things further. The bonded yoke and convergence magnet were used to speed up the manufacturing process, but of course I would be able to make convergence even better since I can spend two hours playing with a yoke and magnets, as opposed to the 60 seconds or whatever they gave it in the factory.

I was actually able to put some 6 pole and 4 pole magnets from another TV behind the cylinder magnet, and I did get center convergence better, but is isn't working exactly as planned. Like it doesn't seem the 6 pole magnets have any effect at all, so I was only really moving red and blue with the 4 pole magnet, which was helpful. I decided not to put any type of magnets directly on the sleeve because I don't know if I could change the magnetic field of it by messing with it too much.

But now convergence on the sides is off more than before, and I don't know if it's from having the rings behind the sleeve magnet, or maybe it now needs a yoke tilt. I'm also wondering if I should just remove the sleeve entirely, so I can completely replace it with the rings. But I also noticed there is some copper wires under it, the same type that the yoke is wound with, so I'm wondering what those do and if I'd screw things up much worse.

And attempting to remove the glue under the yoke sounds risky, if I wanted to adjust that. I've read the same people have damaged yokes attempting this, though others did it successfully. Since it's very hard to know if you've loosened the glue enough with, say, a heatgun, I could see a problem occurning where some glue somehwere on the tube is stil bonded and takes some wires with it or something.

And in the picture I posted above, I drew an arrow pointed at a rubber cap. There's an identical one on the right side. I'm curious if you guys know what might be under those. Because when I put a magnet on that, it alters convergence. but usually by way too much

Getting good side convergence while maintaining good center convergence can be extremely difficult-- especially if its just a single side giving problems. Ive been playing with my new Wei-ya M3129 and thankfully it does not have the same blooming blob issues as the last one I returned, but the right side center red/blue convergence is a bit off (to be fair, so was the other one). Ive been playing with small 1cm/1.5mm neo magnets, convergence strips, ferrous rods and pieces, and I did attempt to tilt the yoke last night. I think it was still fastened with a bit of glue and didnt really move, just flex, but I just quit while I was ahead. I was able to do some things but never able to get the right side as good as the left or center. Theres so much that can go wrong and right now I dont have the heart to go much further on this $700 unit. The picture is actually very nice as is save for some bad side compression in 15KHz mode but theres a cap mod for that that I will take a chance on.

From what Ive read, side convergence is usually combatted with yoke tilt? Specifically, Ive read that up/down tilting of yoke affects side convergence and side to side tilting affects top and bottom convergence, seems unintuitive but perhaps thats how it is. Is that your understanding too? What results did you see from tilting it?

Also, about the wires under the magnetic sleeve, thats normal-- if you pull convergence rings off an adjustable unit, there are also wires underneath them, thats why they work. I dont think Ive seen any that dont have coil/wire under the rings.

[BazookaBen]

It must be the scan velocity modulation coil. You can disconnect it from the neckboard if you prefer the picture without it.

BTW, can you adjust horizontal size, parabola and trapezium? The manual is contradictory as it says they're adjustable but the schematics show there is no EW circuit.

Already have scan modulation disabled in service menu, so that would be great if that's what those coils are, so I wouldn't need to worry about damaging them. Just to be clear, they're under the plastoferrite sleeve on the neck

As for geometry, I haven't messed with that much at all yet, though I plan to experiment in the future. I think I did adjust H size though. I'm not even sure what"parabola" does.

By the way, how are you able to tell whether or not those geometry circuits are present in the schematic?

.From what Ive read, side convergence is usually combatted with yoke tilt? Specifically, Ive read that up/down tilting of yoke affects side convergence and side to side tilting affects top and bottom convergence, seems unintuitive but perhaps thats how it is. Is that your understanding too? What results did you see from tilting it?

Yoke is bonded, so I can't tilt it. I've read a few different methods on how to loosen or cut the glue, but I'm really afraid of damaging it.

I kinda want to remove the plastoferrite sleeve so I can completely replace it with those convergence rings. With those moved an inch forward, I'm thinking that the landing might be better, since they will be farther in front of the electron gun. So right now I need to figure out how to remover that sleeve without damaging it. I don't know if it's glued on or what.

[Josh128]

After consulting Sams online CRT repair bible, it appears to confirm that the only way to fix side (dynamic) convergence is to adjust the depth and tilt of the yoke (and with strips for corners). It says that once you get good center (static) convergence from ring adjustment, no more ring adjustment is necessary and you will have to move to the yoke.

I gather from what you are saying, you have good static convergence, as do I-- but our dynamic convergence needs work. I think your only recourse is to cut the tape/glue and adjust the yoke. I am slowly growing in courage to try and un-stick the yoke on my 3129 to try and help with the right side convergence. Thank God I didnt fuck with the rings as that would have been a mistake, my center convergence is perfect.

I think if you are extremely careful, you should be able to cut the glue/tape and "unbond" the yoke. It should be made just like any other yoke physically, just secured with a ton of glue. I can see how that big old warning sticker does give you pause about attempting it though.

http://www.walshcomptech.com/repairfaq/ ... CRTFAQ_043

[MKL]

It must be the scan velocity modulation coil. You can disconnect it from the neckboard if you prefer the picture without it.

BTW, can you adjust horizontal size, parabola and trapezium? The manual is contradictory as it says they're adjustable but the schematics show there is no EW circuit.

Already have scan modulation disabled in service menu, so that would be great if that's what those coils are, so I wouldn't need to worry about damaging them. Just to be clear, they're under the plastoferrite sleeve on the neck

There must be two wires coming out and going to the neckboard.

As for geometry, I haven't messed with that much at all yet, though I plan to experiment in the future. I think I did adjust H size though. I'm not even sure what"parabola" does.

By the way, how are you able to tell whether or not those geometry circuits are present in the schematic?

Parabola is another term for pincushion. Pin 29 of IC201 is the east-west correction signal but it's not used on this set. It's not necessary when the tube has a deflection angle of 90° or 100°.

The metal clamp that tightens the yoke around the neck is not present here as the yoke is designed to be bonded to the tube. It's the bonding compound that holds it in place.