sci.electronics.repair - 14 new messages in 8 topics - digest

sci.electronics.repair
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==============================================================================
TOPIC: OT: Lithium Cells Exploding
http://groups.google.com/group/sci.electronics.repair/t/181af8dd8c2e6fde?hl=en
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== 1 of 1 ==
Date: Sat, Dec 11 2010 4:52 pm
From: Cydrome Leader

Michael A. Terrell <mike.terrell@earthlink.net> wrote:
>
> "Geoffrey S. Mendelson" wrote:
>>
>> Michael Kennedy wrote:
>> > I recently found out that Lithium cells are no longer allowed in checked
>> > luggage on airplanes in the US.
>> >
>> > Personally I have tortured those lithium button cells and have never had
>> > them do anything really dangerous other than spew some nasty stuff out.
>>
>> There was an Austrian Airlines jet brought down because a shipment of
>> watches had a large number of the lithium cells in them leak in the
>> unpressurized cargo hold and catch fire.
>>
>> The "nasty stuff" is extremely flamable in large quantities.
>
>
> NASA won't allow any litium cells in space. We had to use 'Capstore'
> NVRAM in our products for space applications. Since the cost difference
> was small, we dropped the battery backed NVRAM from our products.

since when does nasa care about stuff catching on fire or exploding, or is
there some sort of higher energy battery failure mode they prefer?

==============================================================================
TOPIC: Samsung and AT&T U-Verse HDMI error?
http://groups.google.com/group/sci.electronics.repair/t/2a432127faab53e5?hl=en
==============================================================================

== 1 of 5 ==
Date: Sat, Dec 11 2010 5:11 pm
From: Ron

On Dec 11, 12:45 pm, John McWilliams <jp...@comcast.net> wrote:
> On 12/11/10 PDT 6:34 AM, Keith wrote:
>
> > Rick:
> > I usually get both but sometimes I also get the error message as well. I guess I will have to try different
> > HDMI cables to see it that is it. Any HDMI cables you would recommend? Thank you.
>
> The ones that cost $110! :-)

Pfft
http://www.crutchfield.com/p_703CARB2M/AudioQuest-Carbon-2-meter.html?tp=2398

== 2 of 5 ==
Date: Sat, Dec 11 2010 8:59 pm
From: UCLAN

Ron wrote:

>>> Rick: I usually get both but sometimes I also get the error message as
>>> well. I guess I will have to try different HDMI cables to see it that
>>> is it. Any HDMI cables you would recommend? Thank you.
>>
>> The ones that cost $110! :-)
>
>
> Pfft
> http://www.crutchfield.com/p_703CARB2M/AudioQuest-Carbon-2-meter.html?tp=2398

Pffft:

http://www.musicdirect.com/product/87492

== 3 of 5 ==
Date: Sat, Dec 11 2010 9:33 pm
From: John McWilliams

On 12/11/10 PDT 8:59 PM, UCLAN wrote:
> Ron wrote:
>
>>>> Rick: I usually get both but sometimes I also get the error message as
>>>> well. I guess I will have to try different HDMI cables to see it that
>>>> is it. Any HDMI cables you would recommend? Thank you.
>>>
>>> The ones that cost $110! :-)
>>
>>
>> Pfft
>> http://www.crutchfield.com/p_703CARB2M/AudioQuest-Carbon-2-meter.html?tp=2398
>>
>
> Pffft:
>
> http://www.musicdirect.com/product/87492

Aaaah, now we're talkin'! The 16 footer is $2,600! Hooooo-Aaaaaah.

--
john mcwilliams

== 4 of 5 ==
Date: Sat, Dec 11 2010 9:55 pm
From: Jeff Liebermann

On Sat, 11 Dec 2010 17:11:27 -0800 (PST), Ron <BigELilE05@msn.com>
wrote:

>On Dec 11, 12:45�pm, John McWilliams <jp...@comcast.net> wrote:
>> On 12/11/10 � PDT 6:34 AM, Keith wrote:
>>
>> > Rick:
>> > � I usually get both but sometimes I also get the error message as well. �I guess I will have to try different
>> > HDMI cables to see it that is it. Any HDMI cables you would recommend? Thank you.
>>
>> The ones that cost $110! :-)

>Pfft
>http://www.crutchfield.com/p_703CARB2M/AudioQuest-Carbon-2-meter.html?tp=2398

Bah Humbug. Only $229 for a 2 meter HDMI cable? That's for
cheapskates. Real audiophiles buy nothing but the best and most
expensive.
<http://www.audioadvisor.com/prodinfo.asp?number=AQHDMIDIA&variation=2>
$1,394.75 for a 2 meter cable is more like it. It comes with a 72VDC
bias to do something to prevent dielectric absorption which allegedly
causes distortion. I like the "long-grain copper". I didn't know
copper has grain.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

== 5 of 5 ==
Date: Sat, Dec 11 2010 10:30 pm
From: John McWilliams

On 12/11/10 PDT 9:55 PM, Jeff Liebermann wrote:
> On Sat, 11 Dec 2010 17:11:27 -0800 (PST), Ron<BigELilE05@msn.com>
> wrote:
>
>> On Dec 11, 12:45 pm, John McWilliams<jp...@comcast.net> wrote:
>>> On 12/11/10 PDT 6:34 AM, Keith wrote:
>>>
>>>> Rick:
>>>> I usually get both but sometimes I also get the error message as well. I guess I will have to try different
>>>> HDMI cables to see it that is it. Any HDMI cables you would recommend? Thank you.
>>>
>>> The ones that cost $110! :-)
>
>> Pfft
>> http://www.crutchfield.com/p_703CARB2M/AudioQuest-Carbon-2-meter.html?tp=2398
>
> Bah Humbug. Only $229 for a 2 meter HDMI cable? That's for
> cheapskates. Real audiophiles buy nothing but the best and most
> expensive.
> <http://www.audioadvisor.com/prodinfo.asp?number=AQHDMIDIA&variation=2>
> $1,394.75 for a 2 meter cable is more like it. It comes with a 72VDC
> bias to do something to prevent dielectric absorption which allegedly
> causes distortion. I like the "long-grain copper". I didn't know
> copper has grain.

Copper?? Copper! Hah. It's gotta be long-grained silver or nothing.....
But I do like the price they're getting for mere copper.... must be over
$10,000 a pound...

--
John McWilliams

==============================================================================
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http://groups.google.com/group/sci.electronics.repair/t/4bd211fe7671ea5a?hl=en
==============================================================================

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==============================================================================
TOPIC: leaving conductors exposed
http://groups.google.com/group/sci.electronics.repair/t/424fa524bd8577b8?hl=en
==============================================================================

== 1 of 2 ==
Date: Sat, Dec 11 2010 7:31 pm
From: "Michael A. Terrell"

William Sommerwerck wrote:
>
> > Can you have the double-insulated symbol on
> > a product with exposed 20V AC conductors?
>
> Because humans aren't likely to be electrocuted by 20V, AC or DC.
>
> But this does raise a question... What about insulation between the primary
> and secondary windings? Its failure could put line voltage on the secondary.

There are high isolation transformers with the windings on separate
bobbins. The efficiency is lower than traditional overlaid winding, but
the two windings aren't close enough for anything less than a lightning
strike from reaching the secondary and there isn't any design that is
safe from a direct strike.

--
For the last time: I am not a mad scientist, I'm just a very ticked off
scientist!!!

== 2 of 2 ==
Date: Sat, Dec 11 2010 8:56 pm
From: Cydrome Leader

s <ymailus@yahoo.com> wrote:
> i got a desk lamp from ebay like the one in the image link below. the
> bulb is held up by two adjustable telescopic rods, exactly the same
> type as you would find on the aerial of a FM radio. they are metal.
>
> i saw the double insulated symbol on the bottom, which go me thinking.
> how did they get the wiring through these rods double insulated, they
> are pretty thin. then i examined the rods. they had joints in them.
> they werent even hollow! there was no wiring. they were the
> conductors.
>
> a quick check with the meter gave 20V AC. thats how it was designed
> to light the bulb .
>
> my question is can you have the double insulated symbol on a product
> with exposed 20V AC conductors?

that's if you believe the markings on the product in the first place.

Can you measure the leakage from either of the antennae to ground?

==============================================================================
TOPIC: tv receivers have puny sound
http://groups.google.com/group/sci.electronics.repair/t/5d73f7ad8fcea692?hl=en
==============================================================================

== 1 of 2 ==
Date: Sat, Dec 11 2010 8:06 pm
From: dplatt@radagast.org (Dave Platt)

In article <ie0tn5$9sp$1@news.eternal-september.org>,
Charles <charlesschuler@comcast.net> wrote:

>This is not a repair question, but I got flamed on the design forum and
>thought that I'd try here. I was labeled a kook and a troll and ... Boy,
>does that group have bunched up underwear!
>
>I have three LCD tvs that work well, but the audio is thin.

The audio drivers in those TVs probably cost all of $1 each in
quantity, and they were probably selected for "it fits" much more than
for their sound quality.

> I know about
>amps and external speakers and surround sound and all of that. Please don't
>recommend external devices, as that is NOT what this post is about.
>
>Is there a technology to build decent speakers into these skinny tv
>receivers? The industry has come up with 3-D, dynamic LED backlighting, and
>other nice features ... but no decent STAND ALONE SOUND.

There are some fairly fundamental problems. As a rule of thumb, if
you want to have loudspeakers with small total volume, decent
low-frequency response, and decent efficiency... well, too bad... you
can pick any two of these, but you won't get all three in a single
device.

Most commercial TV-speaker designs choose small volume and good
efficiency... and lose out on the low frequency response.

If you want to keep the small volume, and get better low frequency
response... well, you lose out on efficiency (need a much bigger
amplifier for a given SPL). You also have problems due to the small
physical size of the driver... it simply can't displace enough air,
when moving back and forth, to create an acceptable SPL at low
frequencies, before it hits its mechanical excursion limits and begins
to distort badly. Also, its voice coil is too small to dissipate much
heat... push more than a very few watts into the driver to overcome
the low efficiency and you'll burn up the voice coil.

>There is a significant market for flat-panel tvs with decent stand-alone
>sound. Any ideas?

One possibility might be to widen the panel by a few inches, and
install multiple small drivers in a vertical line arrangement on each
side... you might get enough driver area to allow for halfway-decent
low frequency response. A similar widened-panel arrangement might be
used with a single flat-panel driver on either side... something
perhaps akin to one of Magnepan's "magneplanar" drivers.

A third possibility might be to conceal some sort of larger driver
behind the panel, with a ported feed out to the side... perhaps
something like a transmission-line loading or porting arrangement.
This might not work for flat-on-the-wall mounting arrangements, but
for articulated mounts there's probably enough space.

Quite simply, to get good low-frequency response at halfway decent
efficiency and distortion levels, you need drivers with a good deal of
frontal area... and you need some back space for them to work in (as a
sealed enclosure, some sort of ported/vented enclosure, or enough
back-wave space for a dipole-radiation arrangement that the low
frequencies don't cancel out).

There are plenty of acoustic tricks one can play, to make a speaker
system sound (subjectively) as if it has more low-bass response than
it does (objectively), and many speaker systems do use these. A
modest boost in the upper-bass "warmth" range can present an illusion
of deep bass, for example.

You might find that your existing flat-panel TV systems can be made to
sound halfway decent, within their physical limitations, by some careful
re-equalization of the audio. You probably can't boost the low bass
very far before the speakers begin to distort, but you could probably
level out the frequency response and "warm it up" a bit, as long as
you're willing to listen at modest volume levels.

It's even possible that some simple physical "tweaking" to the existing
speaker drivers and their (miserable excuse for a real) enclosure,
would clean up the sound somewhat. Sticking some damping materials on
the inside of the plastic case of the TV to damp out resonances in the
case, and maybe adding some wool or polyester batting to tame
resonances within the enclosures, might tame the "peaky" sound a bit.

It might even be worth replacing the drivers with less-awful ones, if
you can find some which fit the enclosure and mounting... probably
won't help the bass much if any but they might be more pleasant to
listen to.

--
Dave Platt <dplatt@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

== 2 of 2 ==
Date: Sat, Dec 11 2010 9:38 pm
From: Jeff Liebermann

On Sat, 11 Dec 2010 17:24:38 -0500, "Charles"
<charlesschuler@comcast.net> wrote:

>Is there a technology to build decent speakers into these skinny tv
>receivers?

No. I used to design marine radios. The problems are similar.
The challenges (or more properly, the problems or nightmares):

1. Thin sound means no bass. To get decent bass, you need a big air
space behind the speaker (bass reflex). Without the air space, you
get a nasty resonance at some point in the speaker. If you like lots
of boom, rattle, and buzz at some low frequency, that's fine. However,
it does get irritating rather quickly. Look at the Bose folded
labyrinth pretzel horn design as an example of how it can be done:
<http://books.google.com/books?id=pAAAAAAAMBAJ&pg=PA86&lpg=PA86>

2. Good bass can be had with a single speaker. No need for two as
the lower frequencies are not very directional. High frequency
tweeters are very different. If you just aim two tweeters straight
ahead, perpendicular to the LCD screen, you get great sound in front
of the TV, and nothing to the sides. With perhaps a 120 degree
viewing angle for the TV, it's difficult to get the same audio
dispersion without using a big ugly horn or acoustic lens for the
highs. Without one, you'll have wide variations in sound quality at
different sitting positions. If you look inside the speakers in a
typical LCD TV, you'll find that they're angled away from the
perpendicular in order to cover the viewers to the sides.

3. Good speakers require a rather solidly built enclosure. If you're
going to pump perhaps 15 watts RMS per speaker into the enclosure, it
has to handle the power without falling apart, breaking solvent welds,
rattling screws loose, breaking component wire bonds, or otherwise
shaking the TV into premature failure. One radio I designed many
years ago had only a 3 watt RMS audio amp and a single 4x6" oval
speaker. In locations where the radio volume was run at full blast to
overcome a high ambient noise level, there were plenty of strange
mechanically induced failures. It was fascinating watching the PCB's
flex at various acoustic resonances under a strobe light.

4. For LCD TV's, vendors are discovering that bigger isn't always
better. You can sell the TV on the basis of a larger screen, but when
the customer takes it home and finds that it doesn't fit in his
entertainment center or whatever, there are problems. The smaller
TV's may have speakers in the "ears" of the screen (on each side), but
the larger TV's often opt for a less space greedy minimalist approach.

5. Plenty more, but I'm tired and want to give up for the evening.

One idea I had was to place the folder speaker horn behind the TV in a
separate enclosure that is the same height and width as the TV. That
leaves plenty of room for the labyrinth. By building the speaker into
a separate enclosure, it can be mechanically isolated from the TV. At
the top or sides of the enclosure are the exit points, which are
directed at the listener with various bizarre shaped reflectors. I
don't know if this will actually work, but it might be a tolerable way
to solve the audio quality problem without resorting to a component
system.

--
# Jeff Liebermann 150 Felker St #D Santa Cruz CA 95060
# 831-336-2558
# http://802.11junk.com jeffl@cruzio.com
# http://www.LearnByDestroying.com AE6KS

==============================================================================
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