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Nanao ms-2931 buzz (fixed!)

Rg111 said:
Take this troubleshooting with a grain of salt. I am no expert on yokes, but a friend and I have removed them. So I'm not completely clueless.

I notice the buzzing getting louder when you turn the camera towards the front of the yoke, as if the sound is being amplified by its cone shape.

If I'm correct, that would point to something in the back creating that sound before it enters the cone.
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Are you suggesting the sound is from the back of the yoke or not actually from the yoke?

I can probably unplug the yoke and confirm that the sound ceases. But I think it’s the yoke, it’s easier to distinguish in person. But hey I have to unplug the yoke anyway right?
 
tiff_lee said:
i'm guessing the sealant is used to bond the yoke to the back of the tube?
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The yoke isn't bonded to the tube.

The sealant is used so you can fill all the small crevices of the yoke.
 
ekorz said:
Are you suggesting the sound is from the back of the yoke or not actually from the yoke?
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The back of the yoke itself. Sorry if I wasn't too clear on that one.

Think about how sound is directed when you place your hands outside your mouth before yelling to someone far away, or how an old school Movie Director's megaphone works.

The sound starts from the back of the megaphone, and is amplified by the cone shape and comes out louder in the front.

interviewBrooksSilentMovie.ashx













I noticed something similar in your video once your camera moved from the front of the yoke, to the back of the yoke, which leads me to believe it's something in the back of the yoke.
 
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Ok, thought maybe you meant the yoke cone was amplifying a noise behind the yoke.

Though, I think it’s more fair to say it is the sound is coming from somewhere inside the cone, not necessarily the back part. Any sound from inside the cone is going to have its waves focused towards the opening of the horn. Nothing is amplifying, it’s just redirecting all sound that would otherwise move radially away from the source.

@nem thanks for the resource. Hope is in sight...
 
Unplugged the yoke. (Hey! It’s connected by the two yoke wires and that’s it! Who knew?)

Turned the monitor on one more time without the yoke, and the buzz is gone. I’ll attempt the hardening fix soon and report back. Thanks all!
 
Yup, uncletom's write up is pretty good. but like i said, you want to stiffen up the yoke structure. The windings are resonating causing the buzz. So you want to basically solidify it. Lacquer is thinner and evaporates quicker/dries faster than varnish so it will most likely take more coats to to solidify over varnish, since varnish has more solids but is harder to apply. Back in the day, and Im sorta dating myself here, we actually used a preheated varnish mix to dip transformer/motor windings to both seal and solidify these to eliminate noise/vibrations/prevent moisture, etc..basically the same could and was done to yokes, etc...at least repairs shops did.
 
Derick2k said:
Yup, uncletom's write up is pretty good. but like i said, you want to stiffen up the yoke structure. The windings are resonating causing the buzz. So you want to basically solidify it. Lacquer is thinner and evaporates quicker/dries faster than varnish so it will most likely take more coats to to solidify over varnish, since varnish has more solids but is harder to apply. Back in the day, and Im sorta dating myself here, we actually used a preheated varnish mix to dip transformer/motor windings to both seal and solidify these to eliminate noise/vibrations/prevent moisture, etc..basically the same could and was done to yokes, etc...at least repairs shops did.
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Would you recommend I find a “shop” of some sort that would have the best or most appropriate chemical? I was just gonna DIY but if it’s as easy as “look up an X kind of business and call to see if they can dip this in their whatever-bath” then I would do that.
 
ekorz said:
Would you recommend I find a “shop” of some sort that would have the best or most appropriate chemical? I was just gonna DIY but if it’s as easy as “look up an X kind of business and call to see if they can dip this in their whatever-bath” then I would do that.
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Nope, I think you can definitely DIY this, Im just remembering how this stuff was done, its been a long time. And honestly you will probably take better care yourself to do it, then shipping it off somewhere. I think if you follow Uncletom's guide you will be fine :thumbup:

Only other thing I can think of if you dont want to do it is checking with shops that rebuild motor windings/transformers, etc..but these guys usually do large industrial stuff, not sure how they would handle a yoke.
 
DIY it is. It sounds like I just need to harden the whole thing, and there’s not really such a thing as too much chemical, so I feel pretty safe just layering it until it doesn’t buzz.

Bought some of this for the lacquer: Sprayon EL2000 CLEAR ELECTRICAL LACQUER SEALER 11 oz Aerosol, SKU #S02000000 https://www.amazon.com/dp/B00DRHSFCS/ref=cm_sw_r_cp_api_i_z87NDbP7S9Y3M

the akrylfog looks like... caulk? I’ll test some different adhesives but if anyone knows what would bond plastic to the tube, since I have no clips, lemme know. Seems to be pretty snug anyway so even hot glue would work I suppose. Probably silicone.
 
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Derick2k said:
Yup, uncletom's write up is pretty good. but like i said, you want to stiffen up the yoke structure. The windings are resonating causing the buzz. So you want to basically solidify it. Lacquer is thinner and evaporates quicker/dries faster than varnish so it will most likely take more coats to to solidify over varnish, since varnish has more solids but is harder to apply. Back in the day, and Im sorta dating myself here, we actually used a preheated varnish mix to dip transformer/motor windings to both seal and solidify these to eliminate noise/vibrations/prevent moisture, etc..basically the same could and was done to yokes, etc...at least repairs shops did.
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So something like this?

https://www.amazon.com/gp/product/B00DGKDOHC/ref=ox_sc_act_title_5?smid=ATVPDKIKX0DER&th=1

I did see some other varnish but they seem to be applied by dipping rather than brushing

https://au.rs-online.com/web/p/prod...VhZSPCh1HTABuEAYYASABEgKS7fD_BwE&gclsrc=aw.ds

https://au.element14.com/electrolub...pla-300605519919|&CMP=KNC-GOO-SHOPPING-958372
 
I just need it to hold it from turning, not lock it in forever! I’ll probably go the hot glue or silicone route.
 
Oh hey. So I was looking at the yoke and heard a small rattle. Shook it a bit and another one of those metal pieces came loose from the same spot.

1xQyFlW_d.jpg


Then I shook it some more and a third popped out.

Guess what doesn’t buzz anymore?

what the heck are these things??
 
They're strips of permalloy. They're there for convergence. Just like the ones that are slid underneath the yoke.
 
nem said:
They're strips of permalloy. They're there for convergence. Just like the ones that are slid underneath the yoke.
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Cool. So I’ll expect a little more work to re-converge this thing then... seems worth it.
 
Just an update... Everything is looking good, but I thought I’d pay my crt-initiation-dues and do the whole purity and static convergence thing while I had it up on the bench.

So far it’s a pretty neat process and not at all awful like I was expecting. Except fuck these corners to hell.
 
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