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[SOLVED] Buzzing Sound from Yoke

kikaso

kikaso

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There's a loud buzzing sound coming from the yoke of my CRT. I thought it was coming from the flyback and so I took this video. Here's what I've noticed so far:
  • At startup, there's what I would call "normal" buzzing coming from the CRT—barely audible with the cabinet closed up even with volume of game off.
  • After 15-30 seconds, the volume of the buzzing goes up and is very noticeable—see video.
  • The loud buzzing goes down after about 10 minutes or so back to normal CRT sound.
  • Sometimes, the volume of the buzzing does not go back down to normal.
  • The volume of the buzzing goes up and down as I press the yoke against the tube.
  • The convergence, focus, etc. all seem fine during gameplay.
I loosened the screw holding the yoke to the neck about one full turn and attempted to press the yoke against the rubber stoppers on the tube. That did not solve the buzzing sound and I am afraid to do more given the risk of electrical shock and potentially damaging the tube.

My questions:
  1. Is the loud buzzing normal for a 30-year old CRT?
  2. If not, is there a fix?
  3. If not normal, does leaving the buzzing result in damage in the long run? (The buzzing doesn't really bother me especially knowing it goes away most of the time and doesn't affect image quality.)
Thanks in advance for your thoughts and advice.
 
ekorz said:
My yoke buzz ended up being some convergence rings that got loose with age.

Nanao ms-2931 buzz (fixed!)
Click to expand...
Thanks for the link!

So you put it all back together minus the loose metal pieces vibrating causing the noise? I’m assuming you just had to add more convergence strips to the tube after rebuilding to get the image looking good. Is that right?
 
Yea, just put it back together after removing the loose metal. honestly I didn’t notice that I needed any more convergence strips
 
So i pulled the yoke this morning but can’t seem to find any loose pieces of metal like @ekorz experienced.

I did find that some plastic tabs around the yoke had separated from the epoxy. Maybe I just need to add silicone? What do people think?
 

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A tip from a friend of mine who is tv technician: just add hot glue. It helps and can be removed easily :)








PS: I have never tried this before but I trust him. He helped me calibrating my cabinet monitor, it works perfect now!
 
DeWitt said:
A tip from a friend of mine who is tv technician: just add hot glue. It helps and can be removed easily :)
Click to expand...
I was going to use super glue but that can be messy and not at all easy to remove. I’ll try hot glue. Thanks!
 
kikaso said:
I did find that some plastic tabs around the yoke had separated from the epoxy. Maybe I just need to add silicone? What do people think?
Click to expand...
Everything is in the thread @ekorz linked to. You could use varnish or lacquer. Basically you want to make sure that the yoke is one solid piece, so parts of it will stop resonating.
 
You can also disconnect the yoke wires and turn it on to make sure it’s quiet, i.e. that the buzz is actually from the yoke.
 
ekorz said:
You can also disconnect the yoke wires and turn it on to make sure it’s quiet, i.e. that the buzz is actually from the yoke.
Click to expand...
I saw you did that in the other thread. Pardon the noob question but how do I go about doing that?
 
What monitor/chassis do you have? It's just a matter of getting AC to the chassis like the cab sends it. You could wire it directly, though I think I just used the wiring from my cab and connected it like normal, just with the monitor up on my bench.
 
It’s a Sanwa PM1723 chassis on a Toshiba 18” tube.

If I’m hearing you correctly, I disconnect the yoke wires and remove the yoke entirely in order to eliminate the rest of the equipment as possible source of buzzing?
 
You don't have to remove the yoke after you've disconnected it. You're eliminating the yoke as a source of the buzzing. Everything else is still up for grabs. Flyback, coils, etc.

Also, turn down the screen pot on the flyback if you're running it for any extended amount of time with the yoke disconnected. Basically when you've disconnected the yoke, all of the brightness of the tube is focused as a dot in the middle.
 
nem said:
Also, turn down the screen pot on the flyback if you're running it for any extended amount of time with the yoke disconnected. Basically when you've disconnected the yoke, all of the brightness of the tube is focused as a dot in the middle.
Click to expand...
Good idea!

So I connected it all up minus the yoke and... no buzzing! I guess it's safe to assume the buzzing is not coming from the chassis but from the yoke.

So my next steps are to try securing the plastic tabs around the yoke via hot glue to see if that fixes the buzzing. If not, I may have to try the varnish / lacquer route which really terrifies me if I'm being honest.
 
That’s a thought.

Hopefully hot glue or lacquer works, though. The buzzing really isn’t that bad. It’s mostly just feeding my need to fix something that I know isn’t working as it should.
 
So I removed the old dried up glue / epoxy and added fresh silicone and that seemed to do the trick; no more loud buzzing.

There’s a faint but high-pitched whine coming from the deflection yoke that I am attributing to resonating on the winding. At this point, I am happy to leave well enough alone—it’s barely audible with the cabinet closed up even with no other sounds in my home. At some point in the future, I may want to add lacquer / varnish to completely stop any resonance-related noises.

Thanks, everyone, for your help and advice!
 

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nem said:
Also, turn down the screen pot on the flyback if you're running it for any extended amount of time with the yoke disconnected.
Click to expand...
One more question; I did as @nem said and turned down flyback voltage when troubleshooting and now I’m curious as to what the “right” setting would be now that I have turned screen pot back up—is there a correct voltage or is that dependent on CRT and age?

I turned master brightness on flyback down to just before screen turned a light blue with horizontal lines. I then fine-tuned via the remote brightness pot the monitor chassis. The neckboard now reads around 360VDC on my multimeter.
 
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