Can bad capacitors affect the convergence of a crt tv? - Page 1
Forum section: electronics / repair

author: OverclockVintage
author_rank: Contributor
timestamp: November 15, 2021, 06:27:27 pm
content: Hi, i have a Sony Wega KV-29FS140 that i have done all kinds of adjustments that don't involve replacement of components or resoldering of components, all that i could actually and i've had some good improvements on the convergence, but it's still far from the average of what most Sony Wega tvs are in that regard, so i am wondering if i may have some bad capacitors. So here i am including a picture of the screen to show you the problem more specifically. Also if the problem can be capacitors then is there a way of knowing witch capacitors can affect and which cannot? Any thoughts? Thanks.

author: eurgenca
author_rank: Regular Contributor
timestamp: November 15, 2021, 07:31:32 pm
content: Hello.No for convergence is not guilty cap. For convergence setup you have magnetic rings on neck of CRT. With this magnets you can curve beam for every color(RGB). But when you start play with this magnets first mark original position.

author: Gyro
author_rank: Super Contributor
timestamp: November 15, 2021, 07:41:13 pm
content: Agreed. Aging capacitors might be responsible for scan linearity issues, but not convergence.Irrc, Trinitron tubes also include small magnets on the bulb of the tube for small localised corrections, but that looks like a diagonal convergence error, which would be more likely adjusted by the magnetic rings on the neck, as eurgenca says.It would also be worth ruling out localised magnetic fields in the area - speaker magnets etc. and degaussing (although that should happen at switch on).

author: OverclockVintage
author_rank: Contributor
timestamp: November 15, 2021, 07:48:39 pm
content: Well i've already did that and also every single internal adjustment possible for this particular tv model plus the ones on the service menu and i am almost sure that i've got close to the best this tv can offer kkkk. So i think it's a matter of the tube itself. Do you guys think the convergence it's too bad the way it is? Thank you guys very much for helping me.

author: james_s
author_rank: Super Contributor
timestamp: November 15, 2021, 08:40:25 pm
content: Unlike most CRTs, Trinitron tubes have dynamic convergence so it is actually possible for an electronic fault to result in poor convergence. I don't know if there are capacitors specifically that are likely to cause that fault, but I would definitely go through it and test all of the electrolytic caps anyway.

author: eurgenca
author_rank: Regular Contributor
timestamp: November 15, 2021, 08:44:06 pm
content: Does deflection coil sit tight on neck? Are some cracks or curved plastic on coil? First try to rotate coil a little bit to right, because left side is lover. How big is this CRT? For large screen is common bad focus on the edges.Look at service manual it is nice descriptive what is for which purpose.Sorry too big for upload.

author: james_s
author_rank: Super Contributor
timestamp: November 15, 2021, 08:46:42 pm
content: No, don't try moving the yoke! If you mess with that you'll never get it lined up right, most deflection yokes are bonded to the tube in newer sets anyway. You have a fault, never try to adjust out a fault, you will just mess it up so bad that the set is scrap.

author: eurgenca
author_rank: Regular Contributor
timestamp: November 15, 2021, 08:59:11 pm
content: Sorry but moving yoke is part of adjustment procedure.

author: Labrat101
author_rank: Unknown
timestamp: November 15, 2021, 09:40:25 pm
content: Moving the main Yoke is only done once when aligned at the factory .As James-s said if you move the yoke you will either crack the neck or mess it up for sure.The only adjustment that you could do is the purity tabs .First you should check all the voltages to the coils that they are within spec . There is also a possibility that the tube has got magnetized.Try degaussing the tube . and leave it in the same orientation when doing so .The bottom Pin cushion is out . And the whole frame is too large and rapping at the edges . reduce the size of the grid .then place a square paper in the centre to help . For a colour tube you must use a patten generator with grid scaler

author: eurgenca
author_rank: Regular Contributor
timestamp: November 15, 2021, 09:57:07 pm
content: And what are you do when coil go bad? In CRT time i personally replaced couple of 10 coils. So I don't know what is so special here, but of course you must know what are you doing...

author: Labrat101
author_rank: Unknown
timestamp: November 15, 2021, 10:26:26 pm
content: Quote from: eurgenca on November 15, 2021, 09:57:07 pmYes ..You probably don't have the right test equipment for aligning this type of tube . ( If you did you wouldn't be asking these questions)Yes you can replace the entire yoke . . You should also read the top section of that pageThe following adjustments should be made when a complete realignmentis required or anew picture tube is installedYes I have aligned Lots of these tubes with the proper alignment .If you are doing it by eye . it can be done by using a thin cord placed from the corners as the tube is not square so the grid you have isstretched there should be about 3/16 of a gap from the top in the middle & bottom to compensate for edge curvature .

author: OverclockVintage
author_rank: Contributor
timestamp: November 15, 2021, 10:44:47 pm
content: I actually had already readjusted the yoke kkkk, as i said i've done everything regarding internal adjustments, buat actually i've regreted messing with the yoke because it took me a long time to just put it back as well as it was in the beginning, because it gets not better than the original positioning. So ok i'm gonna try to reduce vertical and horizontal size of the image and see if i can get better convergence with that. Thanks alot guys.

author: BreakingOhmsLaw
author_rank: Frequent Contributor
timestamp: November 16, 2021, 12:21:00 am
content: Used to work in a Philips CRT factory back in the 90s. Calibrating CRT in production was done in two ways:For run-of-the mill CRT, automatic convergence measurement was done with optical sensors. Philips CRT have a small magnetic ring inside the neck, which was magnetized in the factory with a huge machine called "HFT" that basically measured the tube with a reference deflection coil, created a corrective magnetic field with eight coils around the neck. Then two bigger coils would run a gauss field and "program" the ring in the neck with the correction field. This gave you decent results. Then in a next step on another machine, the customer deflection coil was fitted and "Z-matching" was done, which basically adjusts the position of the deflection coil to the spot where the reference coil was during magnetizing. The coil is then fixed into place by pushing some plastic pins in the corners inwards against the glass cone and welding them shut with ultrasound. The sleeve at the back was tightened as well. Then a robot applied some silicone to further fixate it. Philips CRTs cannot be fixed of the convergence is bad, you have no way of adjusting them in lieu of the sliding magnets around the neck.For higher quality tubes (the ones we made for Bang & Olufsen for example), an additional step was taken. An operator would have it in a test jig and glue strips of magnetic tape to the cone to fine tune it The tube itself was identical, same gun, same deflection coils. Just more manual calibration added to meet higher specs for luxury TV sets from B&O, Loewe, SABA etc.Good times. Calibrating the bloody optical sensors was done in the workshop. Whomever did it would crawl under a huge cardboard box that went over the calibration jig to keep the light out. High-tech, kids!

author: james_s
author_rank: Super Contributor
timestamp: November 16, 2021, 12:29:11 am
content: I used to repair quite a few CRT displays, a friend of mine actually worked in a TV/monitor repair shop back when those were a thing. Every once in a while they would have a set come in that had failed and it would turn out the owner had opened it up and twiddled with every adjustment they could find. They refused service on those sets, although sometimes they would come in and the person would swear they hadn't monkeyed with it but it was clear that somebody had. "Modern" CRT displays (ie those with solid state electronics) don't drift and you should never have to adjust anything inside. If a fault develops you should never try to adjust it out, a component has failed and the failed component needs to be replaced. If you monkey with the adjustments then it will all need to be aligned and it may be difficult to find the necessary information and in some cases special tools are required.

author: eurgenca
author_rank: Regular Contributor
timestamp: November 16, 2021, 06:45:58 am
content: For a lot of things in electronic you need a special tool, but you must think out of the box, And this is the reason why we all go on this forum. And that is correct

author: OverclockVintage
author_rank: Contributor
timestamp: November 18, 2021, 10:10:51 am
content: And what about the linearity is it too bad to the point that could be possible to be related to some component issue?

author: Labrat101
author_rank: Unknown
timestamp: November 18, 2021, 05:42:01 pm
content: Quote from: OverclockVintage on November 18, 2021, 10:10:51 amYes ..There is a greater chance its a bad resistor . Not sure why you are suspecting only a bad cap . I have found many a resistorgone High or Low and they look good by eye . but evil within . That why it was mentioned at the very begin .To check all the voltages , and scope signals before doing any mechanical adjustments.The Sony Trinitron tubes are not as easy to set up . as they use their Patented Grid mesh with 3 separate guns and the dots are ina triangular arrays .

author: andy2000
author_rank: Frequent Contributor
timestamp: November 18, 2021, 09:36:02 pm
content: While not the best, I think the convergence and linearity on the picture would have been considered acceptable when that set was new. I've seen worse. Some CRT/yoke combinations just end up working out better than others due to tolerances. The service manual might even have specs on how far out the convergence can be. If it looks fine when watching normal content from a normal distance, it's fine. It's not a computer or engineering monitor.Sony never used bonded yokes, unlike some companies that did literally glue the yoke to the CRT with epoxy. RCA was a big fan of bonded yokes, and even used a strip magnet rather than the adjustable rings.The rungs are only for center convergence and purity (bean landing). The edge convergence is adjusted by tilting the front of the yoke, and sometimes by electrical adjustments on the yoke.It wasn't unusual for the yoke to gradually slip out of position over time. It would slide back on the neck, and the top would tilt down. Also, the rubber wedges used to shim the front of the yoke in position after adjustment would often fall out. Sony usually glued them in place with silicone adhesive, and I recommend doing the same since double sided tape tends to weaken with age.If the yoke can be tilted up/down or left/right, then it has probably shifted out of position. If it's still held tight, then it's probably fine. Having said that, it's almost always possible to improve on the factory adjustment. They simply didn't have the time to fuss with it for hours on the production line.

author: james_s
author_rank: Super Contributor
timestamp: November 18, 2021, 09:48:05 pm
content: It's true that convergence was never perfect on CRT displays, but the better ones were pretty good, especially Sony. Broadcast studio monitors were made by hand-picking the very best of the best tubes that came off the production line. When the CRT TV market collapsed there was no longer a mass production line to pick tubes off of and it was quite a while between consumer LCD TVs becoming popular and when LCDs became available that were even remotely good enough for broadcast studio work.

author: OverclockVintage
author_rank: Contributor
timestamp: November 19, 2021, 04:11:39 am
content: Labrat101Capacitors age, so i was thinking that it could be that, but if there is such a considerable chance of opening the tv and removing the board just to find out that nothing can be done to improve it, i really don't want to go trough the trouble.andy2000So it's likely that it was always like that, i'll just leave it alone, the yoke i've repositioned it already, and the rubber wedges are quite firm in place.james_sYes, i've being resarching about it just to find out that some flat tube tvs were quite commom to have linearity and convergence imperfections from factory, while some would be much better than others, also some models of Sony Wegas tend to be much better than mine. I would mostly not recommend flat tube tvs, but the Wegas do have great sound quality though, so it may be worth in the end. It's hard to understand why companies put so much effort and money to make thes flat tube tvs, the curved ones were quite fine.