CRT Fetish Thread

skate323k137

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Always one hand behind the back. ALWAYS on an isolation transformer.

A bare arcade CRT, minus an isolation transformer, will fuck your day up.... You become "earth"
 

ChuChu Flamingo

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Do you need one if you're just rotating the yoke? I know for probing with an oscilloscope you want one to both protect it and yourself.

If so any recommendations? I've been reading up a lot on them and most newer ones have a third ground pin so you don't get true isolation until you sever it and are not safe with a "hot" chassis.The set in question is a Sony consumer tv that needs it. It has a color purity problem on one side of the screen (already tried degaussing with my wand).

My procedure would be

-tv on

-one hand behind my back

-wear electricians gloves

-grab plastic when rotating, not the metal

-avoid the neckboard, anode flyback, and the sometimes exposed/insulated terminals near the back of the yoke assembly
 
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skate323k137

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I honestly have NO idea how to safely rotate a yoke. Only one I rotated came to me loose and I just rubber shoed/gloved/etc the fuck up, isolated the tube, and turned it.

YMMV.
 

ChuChu Flamingo

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Ah I see. i am just more curious about the corner cases cause I wouldn't want to be one.
 

skate323k137

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full screen rotation = yoke.

Corner color misalignment = convergence strips

Very easy to do convergence strips, if you follow the "golden rule" (hand behind back, isolated)

I do all my monitor calibrations with a mirror, in this way I can stand behind the monitor and align test pattern without 2nd person.
 

ReplicaX

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You guys are forgetting possibly the 2 most dangerous silent killers on all monitor chassis. B+ depending on the monitor and its state range from 90 - 170VDC. All Chassis have exposed line voltages as the bridge rectifier is on the board.
Those 2 are far more deadly than HV due to amperage.

Also if the monitor is already isolated, you do not need an isolation transformer. READ THE MANUAL.
 

skate323k137

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You guys are forgetting possibly the 2 most dangerous silent killers on all monitor chassis. B+ depending on the monitor and its state range from 90 - 170VDC. All Chassis have exposed line voltages as the bridge rectifier is on the board.
Those 2 are far more deadly than HV due to amperage.

Also if the monitor is already isolated, you do not need an isolation transformer. READ THE MANUAL.

preach
 

ChuChu Flamingo

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I guess the question I was asking is what happens if you are working on a live chassis with no isolation transformer and simply rotating the yoke up or down. Making sure not to touch the copper windings, exposed terminals, neckboards, and all the other stuff I stated above. I've seen people rotate the yoke without a care in the world while on.

I read up in the service manual for sony kv-20v80 that it does state to use a isolation transformer since it is a live chassis (hot). Any recommendations for a isolation transformer replica? Most I see have a ground plug which doesn't provide true isolation. Even if you get an adapter 3 prong to 2 prong a lot still tie neutral to ground so you haven't fixed anything.

But yeah here is how this sony looks.

ItpYgCQ.jpg


Degaussing wand doesn't help much (it doesnt fix it completely and returns after power off). Rotating the crt NSEW it usually just moves it downwards. Having it be on for a little bit makes it a little better. Basically I use this for DDR and want to experiment fixing it for practice. From what I've read and advice i've seen it needs a yoke adjustment up or down. Convergence is off too so I will play with the rings a bit (making note to mark og positions). Nothing much to lose on this set if I do mess it up but it can be RGB modded pretty easily.




Very good information though ReplicaX. I usually stay far away from the exposed terminals of the rectifier/filter capacitors etc for that very reason. Another thing I've noticed online is most know to discharge a crt before removing the chassis, but forget to discharge the filter capacitors.
 
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ReplicaX

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Aye, those areas need to be mindful of.

I read up in the service manual for sony kv-20v80 that it does state to use a isolation transformer since it is a live chassis (hot). Any recommendations for a isolation transformer replica? Most I see have a ground plug which doesn't provide true isolation. Even if you get an adapter 3 prong to 2 prong a lot still tie neutral to ground so you haven't fixed anything.

Any real Isolation Transformer provides isolation between the source and device as the primary and secondary coils are not physically connected. Nor do they share any taps on the winding. Most have ground plugs so the transformer itself is grounded in case of a fault and your safety.

Neutral is only tied to ground at the panel or after the stepdown before your panel. Neutral should never be tied to ground on devices. Otherwise if the device has a chassis ground, you just made all metal on the device live.

Why I tell anyone with Japanese cabs to properly ground them to avoid the risk of shock or stray voltage. (My Q25 has a ground terminal on the back for this exact reason)
 

ChuChu Flamingo

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A lot of the ones I see do exactly what you stated not to if my research is right. The output ground (secondary primary?) is tied to neutral. Of course that is not what you want for working on crts from my reading.

Technicians isolation transformer is what I see people calling what I want.

The ones on amazon don't seem to be true technicians isolation transformers if im reading right. Almost all either need to be configured via opening it and severing the connection or if you're lucky it can be configured with jumpers.

Here is a video I watched which I thought explained it well.

https://www.youtube.com/watch?v=XBsQ3sZ45Fk

Also yeah mad dumb to be running expensive cabinets without proper grounding.
 
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skate323k137

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Really should get around to making a premade board with the AC filter and isolation transformer pre-wired

The safety implications alone are worth it IMO.
 

Tempest

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The yoke is energized on certain crts from what I've seen.

Also here is a crt discord. I would ask on there.

https://discordapp.com/invite/Qc9Tt6g

I popped in over there and they said that my TV looks pretty good except for the vertical size (which I've fixed since that picture). It needs some pincushion adjustment but there doesn't seem to be a way to do that on this model (although the menu is called pincushion). Bottom line, I think it's as good as it's going to get unless there's a secret service menu beyond the one I'm using that I havent found.
 

MKL

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There's also a problem with some bowing inward in the center on the bottom (see the last picture) that I can't figure out how to fix either.

tv_1.jpg

That kind of distortion (called seagull) is due to an imperfect correction of the south pincushion by the relative magnet located on the bottom of the deflection yoke (101 in the pic below). At the factory this distortion was deemed tolerable or else they would have tried to modify the magnetic field of that magnet by adding another small magnet close to it. You could do it now.

yoke0.jpg
 

Tempest

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I do have magnets, but I don't know if they'll over correct the issue. I'm afraid to try and put one near it when it's on because the last time I tried that my hand started getting tingly before I got near it (even I know that's not a good sign). Can I do anything with the magnet that's already there to fix it?
 

MKL

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Maybe the EHT cable was too close. Move it away from the yoke. The magnet on the yoke is in a fixed location so no, you can't do anything with it. The magnets to be placed around the yoke rim need to be weak. In fact they are small bits of magnetized plastoferrite.
 

Tempest

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Maybe the EHT cable was too close. Move it away from the yoke. The magnet on the yoke is in a fixed location so no, you can't do anything with it. The magnets to be placed around the yoke rim need to be weak. In fact they are small bits of magnetized plastoferrite.

Ah ok, the magnets I got are probably way too strong then (they're not rare earth or anything, but they're decent strength). Where does one get magnets that will work with the crt?

EDIT: ok it looks like magnetized plastoferrite are basically sheet magnets. Is that true? Can I cut a little bit off a sheet magnet and stick it to the yoke?

So the EHT cable is the one that goes from the suction cup on the CRT? I can try and move that a little and see if it fixes anything. I assume just touching the cable is safe, it even has a little plastic spacer gizmo on it I can use.
 
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ChuChu Flamingo

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Unless the crt has been discharged best practice would be to use a plastic insulated tool to move it over. The rubber coming from the flyback can form micro cracks due to age, heat, and high voltage being sent through it. Usually this happens with sets that have been on for a long time most notably arcades. You often see this with real old arcade monitors where it looks like someone blew a load all over it trying to seal the high voltage.

Realistically though you are probably safe. Just don't become a corner case for the reasons listed above.
 

Tempest

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Unless the crt has been discharged best practice would be to use a plastic insulated tool to move it over. The rubber coming from the flyback can form micro cracks due to age, heat, and high voltage being sent through it. Usually this happens with sets that have been on for a long time most notably arcades. You often see this with real old arcade monitors where it looks like someone blew a load all over it trying to seal the high voltage.

Realistically though you are probably safe. Just don't become a corner case for the reasons listed above.

Yeah I was just going to grab it by the round little spacer thing anyway since that's non-conductive.

I still need to try that little sheet magnet I have and see if that does anything.
 

MKL

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Where does one get magnets that will work with the crt?

On CRTs. These are the magnets you find on top and bottom of yokes. They can be cut so when I need it I just slice them.

magnets.jpg
 

Tempest

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Wow. Where do you get those? Or did you harvest them from dead CRTs?

I'm going to see if my little sheet magnet does anything this weekend. If not, I may be out of luck.
 

skate323k137

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Wow. Where do you get those? Or did you harvest them from dead CRTs?

I'm going to see if my little sheet magnet does anything this weekend. If not, I may be out of luck.

You can sometimes salvage parts from old CRT's but I only recommend if you know what you're doing.
 

Tempest

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You can sometimes salvage parts from old CRT's but I only recommend if you know what you're doing.

We have some old CRTs here in the lab where I work that probably haven't been turned on in years in the junk pile, but they're computer monitors not TVs. Do computer monitors have magnets in them?
 

Tempest

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Well I tried the magnet tonight but I guess it's either took weak or I have to actually touch it to the yoke (not just get close) to make something happen. Not sure how safe that is to do while it's running.

BTW here is a pic of the insides of the TV. You can see the little plastic spacer thingy (and a lot of dust). I tried moving the cable by touching the spacer, but it's pretty stiff and I think it's where it wants to be (and it didn't change anything when I moved it anyway).

tv_4.jpg
 

MKL

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You see that magnet? There's one on the bottom too. That's where you need to place and eventually glue your magnet.

yoke9.jpg
 
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