TVs and unshielded speakers

[whit3rd]

On May 22, 7:43 pm, Smitty Two <prestwh...@earthlink.net> wrote:

In article <4a172006$0$6673$703f8...@textnews.kpn.nl>,
 Sjouke Burry <burrynulnulf...@ppllaanneett.nnll> wrote:

Jo wrote:
What kind of damage can be done to CRT TVs from unshielded speakers?

Would you humor me with an experiment? Move the boombox away, and see
whether the picture changes, then put it back.

Just to be clear: a magnet outside the TV can magnetize a bit of steel
inside
the TV, so it takes BOTH moving the source AND cycling the TV's
internal degaussing coil to rid oneself of the color.

Unplug the TV for at least 5 minutes to be sure it's cold, then plug
it in and turn it on, to trigger the degausser cycle.

This should be done if magnetized items are moved to or from the TV's
vicinity, or even (for careful work) when the compass orientation of
the TV is changed. Any color splotches that remain, require purity
magnet adjustment (if you have to ask what that means, you should
let someone else do it).

 

[Ron]

David Nebenzahl wrote:

On 5/23/2009 2:49 AM Ron spake thus:

Smitty Two wrote:

In article <4a172006$0$6673$703f8584@textnews.kpn.nl>,
Sjouke Burry <burrynulnulfour@ppllaanneett.nnll> wrote:

Jo wrote:

What kind of damage can be done to CRT TVs from unshielded
speakers? Do boomboxes from around 2002 usually have shielded
or unshielded speakers?

A boom box is sitting right under my crt tv as we speak.
Has been there for the last 10 years.
No problem.

Would you humor me with an experiment? Move the boombox away, and see
whether the picture changes, then put it back.

I once put a 30" length of railroad rail on top of my TV. You know, a
bachelor's idea of home decorating. It sat there for a few years, and
never caused any problem with the picture.

When I finally moved it, the color blotches were horrible. But the
external degaussing coil cleared it right up.

Did it have a loco or two on the track? with permanent magnets in
the motors?

Real loco motors (i.e., traction motors) don't have magnets. Use field
coils.

Oh, I thought we were talking about model railway track - I doubt he
could have got a 'Real Loco' on top of his TV

Why whould you put a length of... oh never mind (I used to have a
conrod and piston on top of mine)

Ron

 

[Smitty Two]

In article <RdSdnZe8d439u4TXnZ2dnUVZ8u2dnZ2d@bt.com>,
Ron <ron@lunevalleyaudio.com> wrote:

David Nebenzahl wrote:
On 5/23/2009 2:49 AM Ron spake thus:

Smitty Two wrote:



I once put a 30" length of railroad rail on top of my TV. You know, a
bachelor's idea of home decorating. It sat there for a few years, and
never caused any problem with the picture.

When I finally moved it, the color blotches were horrible. But the
external degaussing coil cleared it right up.

Did it have a loco or two on the track? with permanent magnets in
the motors?

Real loco motors (i.e., traction motors) don't have magnets. Use field
coils.


Oh, I thought we were talking about model railway track - I doubt he
could have got a 'Real Loco' on top of his TV

Why whould you put a length of... oh never mind (I used to have a
conrod and piston on top of mine)

Ron

Yeah, real track. 50 or 100 lbs. of steel, I don't remember quite how
heavy it was.

OT: You gotta hand it to Lionel's founder, Joshua Lionel Cowen. A real
marketing genius. He referred to the real trains on which his toys were
modeled as "prototypes."

 

[GregS]

In article <bc0f3966-3c21-4125-b4e9-c03292ad3d01@u8g2000yqn.googlegroups.com>, whit3rd <whit3rd@gmail.com> wrote:

On May 21, 10:59=A0pm, Jo <AGirlName...@gmail.com> wrote:
What kind of damage can be done to CRT TVs from unshielded speakers?
Do boomboxes from around 2002 usually have shielded or unshielded
speakers?

Television CRTs have internal elements (shadow mask and electrodes)
that can be misaligned, bent, or damaged by a strong magnet.

Speakers usually have strong magnets, BUT those are for the voice coil
and
the field doesn't extend beyond an inch or two. A few compact

You must not have played around much with speakers. Even the shielded ones
have a little effect, and it also depends how well the drivers are made
and the shielding they employ. Its easy to see effects of unshielded
speakers from a foot ot two away.

When drivers are made, they can be designed to have minimal external
fields before shielding. Its a manufacturing design cost thing.

greg

speakers may
have enough field outside the box to distort a color picture (but that
doesn't mean that there's any permanent damage),
but only if you disassemble the speaker will you get any magnetic
parts capable of
doing real, permanent damage. All speaker magnet designs are
shielded
by design, because it's expensive to waste the field on empty space...

I've tested magnetic linear motors (big 'uns, over 20 pounds of magnet
material)
and the field is harmless at a few inches. For a boombox speaker,
maybe
two inches magnet-to-screen is too close. Four inches should be OK.

 

[martin]

On May 22, 6:59 am, Jo <AGirlName...@gmail.com> wrote:

What kind of damage can be done to CRT TVs from unshielded speakers?
Do boomboxes from around 2002 usually have shielded or unshielded
speakers?

A strong magnetic field close to a CRT tv or monitor could magnetise
the steel shadow mask. This will lead to purity errors or splodges of
colour as the beams are diverted from their usual path, hitting the
wrong phosphors. All CRT's have a degauzing circuit built around the
tube, which will only operate from cold - so leave set off for five
mins before trying. The shadowmask is allowed to move as it heats up,
they can dissipate many watts, so it is unlikely to distort unless an
extremely powerfull magnet is placed right on the screen. Usually only
happens when it has been dropped. If the internal degauzing cct does
not do the job then a degauzing wand or similar ( a coil with
alternating magnetic field) is used. this you have to start close to
the set and move away while rotating untill you are out of range.
inverse square law applies. speakers from2002 that are used for A/V
will certainly(almost) to be sheilded.

 

[JB]

"Smitty Two" <prestwhich@earthlink.net> wrote in message
newsrestwhich-43A424.21133925052009@newsfarm.iad.highwinds-media.com...

In article <RdSdnZe8d439u4TXnZ2dnUVZ8u2dnZ2d@bt.com>,
Ron <ron@lunevalleyaudio.com> wrote:

David Nebenzahl wrote:
On 5/23/2009 2:49 AM Ron spake thus:

Smitty Two wrote:



I once put a 30" length of railroad rail on top of my TV. You know,
a
bachelor's idea of home decorating. It sat there for a few years,
and
never caused any problem with the picture.

When I finally moved it, the color blotches were horrible. But the
external degaussing coil cleared it right up.

Did it have a loco or two on the track? with permanent magnets in
the motors?

Real loco motors (i.e., traction motors) don't have magnets. Use field
coils.


Oh, I thought we were talking about model railway track - I doubt he
could have got a 'Real Loco' on top of his TV

Why whould you put a length of... oh never mind (I used to have a
conrod and piston on top of mine)

Ron

Yeah, real track. 50 or 100 lbs. of steel, I don't remember quite how
heavy it was.

OT: You gotta hand it to Lionel's founder, Joshua Lionel Cowen. A real
marketing genius. He referred to the real trains on which his toys were
modeled as "prototypes."

Don't tell me... This was to stop the buzz from the internal speaker grill?

Why not bend the track and wheel the TV around on it?

 

[Michael A. Terrell]

JB wrote:

Don't tell me... This was to stop the buzz from the internal speaker grill?

Why not bend the track and wheel the TV around on it?

50 - 100 pounds would only be a few feet of standard rail used in the
US. I had a one foot piece of scrap rail someone had ground into a
crude anvil that weighed 45 pounds.


--
You can't have a sense of humor, if you have no sense!

 

[Smitty Two]

In article <UZfTl.862$Cc1.18@nwrddc01.gnilink.net>,
"JB" <nospam@goofball.net> wrote:

Don't tell me... This was to stop the buzz from the internal speaker grill?

Nah, just home decor. I had a few pieces of railroad junk lying around.
I had actually just sold the TV when I removed the rail and the colors
went haywire. They buyer got real nervous, but I hit it with my
degaussing coil and cleared it right up. I guess the rail had become
part of the magnetic field of the CRT, gradually over time.

 

[Bob Larter]

Jo wrote:

What kind of damage can be done to CRT TVs from unshielded speakers?

Nothing that can't be fixed with a degaussing wand. If the colours on
your screen are distorting, your speakers are too close.

Do boomboxes from around 2002 usually have shielded or unshielded
speakers?

Unshielded, most likely.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

 

[Bob Larter]

Jo wrote:

On 22 May, 06:05, "William Sommerwerck" <grizzledgee...@comcast.net
wrote:
What kind of damage can be done to CRT TVs from unshielded
speakers?
Little or none.

Several years ago, as an experiment, I shut off a powerful bulk tape eraser
right to a 36" Trinitron to see what happened. It produced what was
apparently a permanent color splotch that would not go away, no matter what
I did.

When the set was moved to my bedroom in March, the splotch magically
vanished. I was told that my original "abuse" has caused the aperture grill
wires to "tangle", and that moving (and therefore vibrating) the set had
made them come loose. In fact, Sony had a guy on the production line who
whacked CRTs with a rubber mallet to prevent or reverse this.

A TV set's automatic degaussing coil can remove all but the worst
magnetization from the shadow mask. It simply isn't something to worry
about.

Another poster said "All speaker magnet designs are shielded by design,
because it's expensive to waste the field on empty space." This is
misleading. Simply blocking the external magnetic field does not make it
available to strengthen the field around the voice coil. Rather, many, if
not most, speaker magnets are "shielded" by using two magnets, arranged so
that their fields add at the voice coil, but largely cancel outside.



Last night I realized there was a green spot at the top of my TV
screen. That's when I realized some jerk had put their boombox right
on top the TV earlier in the day. There's two inches between the spot
and the top of the TV. So the speaker in the boombox was probably
three to four inches away from the spot. It seems like that boombox is
what caused the green spot. It would be too much of a coincidence for
the spot to appear the same day the boombox had been placed on the TV.

So, will this go away by itself?

Eventually.

It sounds like you're saying the
degaussing thing should fix it.

Yes. Eventually. Each time you power-cycle the TV, it should fade, or
even go away. You can fix it in one go with a degaussing wand, but
that's probably overkill for a small splotch.

I would imagine something like this
would void the warranty and the free repair program thing I purchased.

Nah, if they don't see it themselves & you're not silly enough to tell
them, it'll be fine.


--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------

 

[Bob Larter]

William Sommerwerck wrote:

They are only strong enough to counter the earth's magnetic field.
If you put a magnet close enough to magnetize the CRT, the
degauser will probably never be able to undo it.

Have you ever tried it? Or are you just theorizing?

Why don't you actually do it, then report back what you find?

<nods> From experience, I've found that the TVs own degaussing coil can
deal with a surprising amount of magnetisation.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------