sci.electronics.repair - 25 new messages in 9 topics - digest

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

sci.electronics.repair@googlegroups.com

Today's topics:

==============================================================================
TOPIC: Electronic curiosities
http://groups.google.com/group/sci.electronics.repair/t/92fb1a53d8547e80?hl=en
==============================================================================

== 1 of 14 ==
Date: Sun, Jan 16 2011 12:50 am
From: Sjouke Burry

David Nebenzahl wrote:
> On 1/15/2011 10:14 PM Jeff Liebermann spake thus:
>
>> On Sat, 15 Jan 2011 19:47:23 -0800, David Nebenzahl
>> <nobody@but.us.chickens> wrote:
>>
>> Talk about off topic... sigh.
>
> Hey, at least it's about *electronics* ...
>
>>> 1. TRF:
>>>
>>> In the section on modulation, demodulation and other radio-related
>>> stuff one book brings up "the tuned radio-frequency receiver"
>>> before discussing superhet, as one would expect. But they say;
>>>
>>> During the evolution of radio, the tuned-radio-frequency (TRF)
>>> receiver was used to receive AM signals. Today, a few special
>>> applications still use TRF receivers.
>>>
>>> Now, they go on to explain why TRF is inferior to superheterodyne.
>>> But I'm curious: are there still any radios that use TRF? and why?
>>> (Keep in mind this book was written in 1979).
>> Yes, but it's not obvious or really TRF. The reason superheterodyne
>> receivers were invented was that decent narrow band LC or crystal IF
>> bandpass filters were not tuneable and didn't work well at higher RF
>> frequencies. About 45MHz was as high as they went before going exotic
>> with SAW devices.
>>
>> These daze, dramatically improved semiconductor technology has
>> produced chips that work at almost any useful RF frequency. No more
>> need to downconvert when the IF filtering is done by a DSP (digital
>> signal processor). Instead of TRF, it's now called "direct
>> conversion". There's no local oscillator, no mixer, for fixed IF
>> filter, and probably no LC devices anywhere. Just a ceramic bandpass
>> filter (or duplexer) some gain, an A/D converter, and a DSP for
>> demodulation. Most GPS, Wi-Fi, and cellular chipsets work this way.
>> <http://en.wikipedia.org/wiki/Direct-conversion_receiver>
>
> OK, so this is why I absolutely *hate* Wikipedia. Here's the lead
> paragraph in the article:
>
> In telecommunication, a direct-conversion receiver (DCR), also known as
> homodyne, synchrodyne, or zero-IF receiver, is a radio receiver design
> that demodulates the incoming signal by mixing it with a local
> oscillator signal synchronized in frequency to the carrier of the wanted
> signal. The wanted modulation signal is obtained immediately by low-pass
> filtering the mixer output, without requiring further detection. Thus a
> direct-conversion receiver requires only a single stage of detection and
> filtering, as opposed to the more common superheterodyne receiver
> design, which converts the carrier frequency to an intermediate
> frequency first before extracting the modulation, and thus requires two
> stages of detection and filtering.
>
> Now, class, how many things are wrong here? (And please correct *me* if
> I'm incorrect):
>
> o First of all, superhet receivers have only one stage of detection and
> filtering, not two, after the last IF stage, right? (I suppose there may
> be some filtering in or around the mixer stage, but I don't think that's
> what they're claiming, which I assume is filtering out the carrier.) So
> where do they get "two stages of detection and filtering"?
>
> o Is their explanation of how DCR works even correct? I don't understand
> the business of mixing the signal with a LO signal: why would you do
> that? They're a little vague: does "synchronized in frequency to the
> carrier" mean *exactly* the same frequency as the carrier (???), or some
> other frequency to produce a sum or difference frequency? (In which
> case, we're back to IF, aren't we, so what's "direct conversion" about this?
>
> If I were in front of a firing squad and had to try to describe DCR
> without actually knowing what it is, I'd guess(tm)(R) that it's a bunch
> of tuned RF stages followed by a detector.
>
> Anyhow, I think I've shown that even if I'm way off base, Wikipedia
> articles tend to be extremely badly written, if not outright full of
> doubtful information. What else would one expect of the "encyclopedia"
> that any PlayStation-playing, junk-food wolfing pimple-faced
> junior-high-school student can edit?
>
>
The story above sounds like descibing a Single Sideband
receiver, where you indeed have to mix in a carrier to detect things.

== 2 of 14 ==
Date: Sun, Jan 16 2011 1:49 am
From: "Geoffrey S. Mendelson"

David Nebenzahl wrote:
> o First of all, superhet receivers have only one stage of detection and
> filtering, not two, after the last IF stage, right? (I suppose there may
> be some filtering in or around the mixer stage, but I don't think that's
> what they're claiming, which I assume is filtering out the carrier.) So
> where do they get "two stages of detection and filtering"?

Not really. While there only needs to be one stage of filtering, it is
common in high end receivers (ham radio and millitary, not audiophile)
to have multiple stages of filtering. So for example, if you have a tripple
conversion receiver you often see filters at the final two.

They are cascaded, meaning you might have a 2.4kHz filter at the 2nd if, and
a 1.8kHz one at the third. Or a 600Hz at the second and a 250Hz at the third.

They are also used as "roofing" filters for DSP filters. If you have a
DSP filter capable of adjustable bandwidth from 6kHz to 100Hz, you may see
a roofing filter (6Hz) in front of it. Since up until a few years ago IF DSP
filters were limited to low frequencies, such as 455kHz, you would see the
roofing filter in the second IF, say 8.8mHz or 10.7mHz, and the DSP at 455kHz.

Now you see them in both places.

> o Is their explanation of how DCR works even correct? I don't understand
> the business of mixing the signal with a LO signal: why would you do
> that? They're a little vague: does "synchronized in frequency to the
> carrier" mean *exactly* the same frequency as the carrier (???), or some
> other frequency to produce a sum or difference frequency? (In which
> case, we're back to IF, aren't we, so what's "direct conversion" about this?

If you mix two signals, you get 4, the originals, plus the sum and the
difference. Sounds familar correct. Instead of mixing two signals 455kHz,
or 10.7 mHz, or whatever apart, a DC receiver mixes them with much closer
frequencies, for example, 800Hz for CW (morse code) or even for audio.

In that case you mix the locally generated signal and the distant one
put them through an audio filter and viola, you have a signal. The problem
with that is they are notoriously poorly selective, and if you are scanning
the ham bands in a large city, you may end up with Rush Limbaugh every few
kilohertz. :-(

Now they are most often used in cheap (and I mean cheap) ham radios usually
kits. Since mixer chips, if filters, etc are so easily and cheaply available,
most radios in the $100 plus range are single stage superhets instead.

> If I were in front of a firing squad and had to try to describe DCR
> without actually knowing what it is, I'd guess(tm)(R) that it's a bunch
> of tuned RF stages followed by a detector.

Rarely. No one bothers with the TRF stages. They tend to be expensive and
unless you have a junk box full of multistage capacitors too costly to make.

> Anyhow, I think I've shown that even if I'm way off base, Wikipedia
> articles tend to be extremely badly written, if not outright full of
> doubtful information. What else would one expect of the "encyclopedia"
> that any PlayStation-playing, junk-food wolfing pimple-faced
> junior-high-school student can edit?

Actually the wikipedia is one of the better sources of information available
today. The paper version of the encyclopedia that used to be given away with
CD ROM drives in the mid 1990's (not Encarta, the other one) was worse.

It's just that it's uneven. Some articles are very well researched and
documented. Others are just an exposition of a (or conflicting) point of
view.

That led me, years ago to come up with Mendelson's Corollary to Godwin's
whatever. In it's simplest form replace "calling someone a NAZI" with quoteing
from the wikipedia. :-)

http://en.wikipedia.org/wiki/Godwin%27s_law

Meanwhile there are many good electronics books which have goneout of
copyright and are being preserved by people scanning them. Some are
available free for dowload, some are sold often for the cost of a blank
CD and shipping.

They make great reading and reference. However to keep it modern, the nook
does not display scanned PDF files well, it has too small a screen, and no
zoom and rotate. The iPad does it wonderfully. I can't comment on the color
nook or any form of the kindle, if someone else can, please do.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.

== 3 of 14 ==
Date: Sun, Jan 16 2011 3:38 am
From: "William Sommerwerck"

> Another book (which I frankly don't like as much since
> it's so math-heavy: wouldn't electronics be so easy to
> learn if all that goddamn math didn't get in the way?)...

I hope you're joking, because without that math, you can't begin to truly
/understand/ electronics. Mathematics is used to model the physical world.
When you understand the math, you have a much better comprehension of the
physics involved.

== 4 of 14 ==
Date: Sun, Jan 16 2011 3:42 am
From: "William Sommerwerck"

>> The reason superheterodyne receivers were invented was
>> that decent narrow band LC or crystal IF bandpass filters
>> were not tuneable and didn't work well at higher RF
>> frequencies.

> ** Total hogwash.
> That has nothing to do with the invention and wide adoption
> of superhet radios.

That's not what the textbooks state. The stated advantages of superhet
receivers are obvious. Care to give another explanation?

== 5 of 14 ==
Date: Sun, Jan 16 2011 3:55 am
From: "William Sommerwerck"

> First of all, superhet receivers have only one stage of detection
> and filtering, not two, after the last IF stage, right?

Wrong. The conversion of the RF signal to the intermediate frequency is a
form of detection (ie, non-linear mixing). The IF stages provide filtering
that removes the unwanted components of the mixing process.

> o Is their explanation of how DCR works even correct? I don't
> understand the business of mixing the signal with a LO signal:
> why would you do that?

Ever heard of a product detector?

> Anyhow, I think I've shown that even if I'm way off base, Wikipedia
> articles tend to be extremely badly written, if not outright full of
> doubtful information.

Badly written, yes. Some articles need a thorough re-write.

Doubtful information? I don't think so. In areas I'm knowledgeable about, I
find Wikipedia remarkably accurate.

> What else would one expect of the "encyclopedia" that
> any PlayStation-playing, junk-food wolfing pimple-faced
> junior-high-school student can edit?

What kind of useful criticism can we expect from someone who doesn't seem to
know much about receiver design?

By the way, the last "GE Transistor Manual" had a classic "direct
conversion" (???) FM tuner (p385) that had only one inductor and no bandpass
filters. (45 years later, I still don't understand how it works.) I'd wanted
to build it, but the transistors were expensive -- the parts came to close
to $100.

== 6 of 14 ==
Date: Sun, Jan 16 2011 3:56 am
From: "Phil Allison"

"William Sommerwanker is a Lying Cunt "

>>> The reason superheterodyne receivers were invented was
>>> that decent narrow band LC or crystal IF bandpass filters
>>> were not tuneable and didn't work well at higher RF
>>> frequencies.
>
>> ** Total hogwash.
>>
>> That has nothing to do with the invention and wide adoption
>> of superhet radios.
>
> That's not what the textbooks state.

** Bollocks they do.

Go to hell you fucking rabid, ASD fucked shit head.

== 7 of 14 ==
Date: Sun, Jan 16 2011 3:56 am
From: "William Sommerwerck"

> The story above sounds like descibing a single sideband
> receiver, where you indeed have to mix in a carrier to detect things.

Product detectors can be used for AM reception. They have advantages over
envelope detection -- but I don't remember what they are.

== 8 of 14 ==
Date: Sun, Jan 16 2011 4:00 am
From: "William Sommerwerck"

> Rarely. No one bothers with the TRF stages. They tend
> to be expensive and unless you have a junk box full of
> multistage capacitors too costly to make.

Many modern /high-performance/ receivers omit the RF stage (such as the Sony
DSP FM tuner), or allow you to bypass it (many ham receivers).

== 9 of 14 ==
Date: Sun, Jan 16 2011 4:54 am
From: "Geoffrey S. Mendelson"

William Sommerwerck wrote:

> Many modern /high-performance/ receivers omit the RF stage (such as the Sony
> DSP FM tuner), or allow you to bypass it (many ham receivers).

Ham receivers omit it because most hams don't need or want it. Since you are
going to be transmitting into a ham antenna, it needs to be resonant or appear
to be resonant.

A resonant antenna, unless it is 100% a resistor, is not resonant on frequencies
you don't want, so they are signifcantly reduced in strength anyway.

If the antenna is not resonant, a device called a "tuner" is used to make it
appear resonant to the transmitter (it does not affect the actual antenna).
In the process of "tuning the antenna", as it were, it detune signals away from
the frequency desired, so in practice it acts as a TRF stage.

For reception only the device is called a pre-selector, although sometimes they
are also called tuners, because they contain the same circuity.

Early (pre WW-II and soon after) TV sets used TRF receivers because of both
the lack of competing signals and the very wide bandwidth needed. As the bands
became more crowded (signals receivable > 1), more services used nearby
frequencies and receiver sophistication increased they moved to superhets.

Eventualy they went to digital sythesizers with mixers, filters and decoders
on a chip. Digital TV receivers are the same thing, except instead of the
"receiver" chip outputing a video signal and an audio signal, it outputs a
bit stream to a decoder chip.

Going back to the other discussion (ducks) that's the irony of DVB-T versus
ATSC. The RF part of the receiver is so generic and adjustable "on the fly",
that it can tune almost anything, the video stream for both is MPEG TS
(transport stream) data, it's the encoding of the bit stream in between.

ATSC was chosen specificaly NOT to be the same as DVB-T.

Someone already sells a chipset to laptop manufacturers to give them ATSC/DVB-T
reception capability, which gives you a TV set that will work almost anywhere.
The TS decoding is done by program in the CPU, so it can support any changes
that come down the line as it where.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.

== 10 of 14 ==
Date: Sun, Jan 16 2011 5:34 am
From: "William Sommerwerck"

>> Many modern /high-performance/ receivers omit the RF stage
>> (such as the Sony DSP FM tuner), or allow you to bypass it
>> (many ham receivers).

> Ham receivers omit it because most hams don't need or want it.
> Since you are going to be transmitting into a ham antenna, it
> needs to be resonant or appear to be resonant.

What does this have to do with the perceived need for an RF stage at the
receiver?

== 11 of 14 ==
Date: Sun, Jan 16 2011 7:29 am
From: "Geoffrey S. Mendelson"

William Sommerwerck wrote:
> What does this have to do with the perceived need for an RF stage at the
> receiver?

Read the rest of the posting, it explains why.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.

== 12 of 14 ==
Date: Sun, Jan 16 2011 9:40 am
From: "William Sommerwerck"

>> What does this have to do with the perceived need
>> for an RF stage at the receiver?

> Read the rest of the posting, it explains why.

I did. It was even more confusing.

== 13 of 14 ==
Date: Sun, Jan 16 2011 10:29 am
From: "Geoffrey S. Mendelson"

William Sommerwerck wrote:
>>> What does this have to do with the perceived need
>>> for an RF stage at the receiver?
>
>> Read the rest of the posting, it explains why.
>
> I did. It was even more confusing.

Ok, maybe this will make more sense.

Hams either use resonant antennas or antenna tuners.

Resonant antennas by virtue of the fact they are resonant in-band, are not
resonant out of band and therefore reduce out of band signals.

Antenna tuners (for reception) act as preselectors which reduce out of band
signals. In practice and design, they are TRF stages.

So if you buy a ham radio with an antenna tuner, it may not have a tuned
front end as specfied, but in reality it does.

Geoff.

--
Geoffrey S. Mendelson N3OWJ/4X1GM
Those who cannot remember the past are condemned to misquote it.

== 14 of 14 ==
Date: Sun, Jan 16 2011 10:31 am
From: Meat Plow

On Sun, 16 Jan 2011 03:38:51 -0800, William Sommerwerck wrote:

>> Another book (which I frankly don't like as much since it's so
>> math-heavy: wouldn't electronics be so easy to learn if all that
>> goddamn math didn't get in the way?)...
>
> I hope you're joking, because without that math, you can't begin to
> truly /understand/ electronics. Mathematics is used to model the
> physical world. When you understand the math, you have a much better
> comprehension of the physics involved.

Math in basic electricity is fundamental learning. You can't begin to
understand electronic circuits with inductance/impedance/reactant/etc..
Things like low pass high pass filters, simple RC circuits, tuned circuits
oscillators. These are the very basics. Understanding trigonometry and
algebra are also a must.

--
Live Fast, Die Young and Leave a Pretty Corpse

==============================================================================
TOPIC: WTB ICL7149CM44
http://groups.google.com/group/sci.electronics.repair/t/86e85510deca02fc?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Jan 16 2011 1:38 am
From: Bo-Lennart

Hi...I wonder if someone have an IC, for sale, in their junk-box.
The IC is labeled ICL7149CM44.
It's a 3 3/4 digit auto-range DVM circuit.

Best regards from SWEDEN
Bo-Lennart Karlsson

==============================================================================
TOPIC: Lidl and Aldi, UK at the moment
http://groups.google.com/group/sci.electronics.repair/t/2f22b65a16216aa2?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Jan 16 2011 3:42 am
From: "N_Cook"

N_Cook <diverse@tcp.co.uk> wrote in message
news:igmrvn$eke$1@news.eternal-september.org...
> Aldi 20 GBP ultrasonic clreaner 500mL, 50W Delta GT 7810A.
> Not had a use for one in decades, will it be another unused toy?
>
> Lidl unknowingly has .3 x .45m vintage speaker grill, purporting to be
> dining place-mats. About 30 percent open weave ( not print) neutral
> coloured, black cream and grey in a sort of art deco slightly wavy
,broken
> linear pattern, 1GBP a sheet
>
>

Out of focus but gives the pattern, inch and cm divisions on the laid over
ruler
http://diverse.4mg.com/speaker_cloth.jpg
matt 0.5mm threads PVC/Polyester maker Meradiso

==============================================================================
TOPIC: OT: Big boys power cable jointing - or not?
http://groups.google.com/group/sci.electronics.repair/t/53e189613358ab92?hl=en
==============================================================================

== 1 of 3 ==
Date: Sun, Jan 16 2011 3:46 am
From: "N_Cook"

Local power cut last week , the errant joint was laid by the trench so I had
to nose.
http://diverse.4mg.com/power_cable1.jpg
I laid a foot ruler laid over for scale. A few hundred houses affected but I
assume this cable only supplied a few dozen, then the linesmen isolated the
area transformer to fix the break , or do they work live? .
Two cable ends marked by "O" . Tar infill not obviously burnt, just what
seems to be an inadequate crimp had partly melted off the left hand end. I
somehow expected something like a phosphorous cauldron like they use for
welding railway line - not a crimp.
And certainly not an open crimp as showing the flute betwen the "o"s in this
closeup
http://diverse.4mg.com/power_cable2.jpg
Orange is probably clay pipe surround, along with lead sheet inside that and
then tar. Remaining cables showed no damage so no shorts.
The end of the cable is cut clean across the wire strands and no sign of any
brazing or the like. Wire strops and marine hawsers use a closed ring crimp
hydraulically compressed on. How much of a bang would such 1 inch diameter
cable failure make a couple of feet underground?

== 2 of 3 ==
Date: Sun, Jan 16 2011 8:30 am
From: "Michael Kennedy"

"N_Cook" <diverse@tcp.co.uk> wrote in message
news:igulrq$2rd$2@news.eternal-september.org...
>
> Local power cut last week , the errant joint was laid by the trench so I
> had
> to nose.
> http://diverse.4mg.com/power_cable1.jpg
> I laid a foot ruler laid over for scale. A few hundred houses affected but
> I
> assume this cable only supplied a few dozen, then the linesmen isolated
> the
> area transformer to fix the break , or do they work live? .
> Two cable ends marked by "O" . Tar infill not obviously burnt, just what
> seems to be an inadequate crimp had partly melted off the left hand end. I
> somehow expected something like a phosphorous cauldron like they use for
> welding railway line - not a crimp.
> And certainly not an open crimp as showing the flute betwen the "o"s in
> this
> closeup
> http://diverse.4mg.com/power_cable2.jpg
> Orange is probably clay pipe surround, along with lead sheet inside that
> and
> then tar. Remaining cables showed no damage so no shorts.
> The end of the cable is cut clean across the wire strands and no sign of
> any
> brazing or the like. Wire strops and marine hawsers use a closed ring
> crimp
> hydraulically compressed on. How much of a bang would such 1 inch diameter
> cable failure make a couple of feet underground?
>
>

Wow thats completely different than what I have ever seen in the USA. I have
never encountered clay pipe or tar before.. Well aside from tar like
substance inside of the waterproofing housing for crimps..

== 3 of 3 ==
Date: Sun, Jan 16 2011 10:56 am
From: Baron

N_Cook Inscribed thus:

>
> Local power cut last week , the errant joint was laid by the trench so
> I had to nose.
> http://diverse.4mg.com/power_cable1.jpg
> I laid a foot ruler laid over for scale. A few hundred houses affected
> but I assume this cable only supplied a few dozen, then the linesmen
> isolated the area transformer to fix the break , or do they work live?
> . Two cable ends marked by "O" . Tar infill not obviously burnt, just
> what seems to be an inadequate crimp had partly melted off the left
> hand end. I somehow expected something like a phosphorous cauldron
> like they use for welding railway line - not a crimp.
> And certainly not an open crimp as showing the flute betwen the "o"s
> in this closeup
> http://diverse.4mg.com/power_cable2.jpg
> Orange is probably clay pipe surround, along with lead sheet inside
> that and then tar. Remaining cables showed no damage so no shorts.
> The end of the cable is cut clean across the wire strands and no sign
> of any
> brazing or the like. Wire strops and marine hawsers use a closed ring
> crimp hydraulically compressed on. How much of a bang would such 1
> inch diameter cable failure make a couple of feet underground?

About 20 years ago I was working on a factory site, when there was a
muffled pop and the lights went out, the factory grinding to a halt.

Out in the yard was a transformer and switch gear inside a brick
enclosure. No obvious signs of damage. The electricity board
engineers showed up and started to inspect the area.

Suddenly without any warning one of the engineers had one leg disappear
up to his knee through the tarmac. The surface had collapsed under his
weight into a cavity right where the cable had blown out. It took
several days to fix.

They put in a new transformer and feed cable. They used a hydraulic
crimping machine to make the joints in the cables, then potted the
whole lot in epoxy resin. I still have a new unused resin pack that I
was given from that repair. Must be well out of date by now... ;-)

--
Best Regards:
Baron.

==============================================================================
TOPIC: XXX HOT PHOTOS&VIDEOS
http://groups.google.com/group/sci.electronics.repair/t/c681bf242442daac?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Jan 16 2011 6:04 am
From: SAILAJA LOVES U

==============================================================================
TOPIC: AA-sized conductor (fake battery) wanted
http://groups.google.com/group/sci.electronics.repair/t/33083a4b1e46ccc0?hl=en
==============================================================================

== 1 of 2 ==
Date: Sun, Jan 16 2011 7:21 am
From: "Michael A. Terrell"

Baron wrote:
>
> D Yuniskis Inscribed thus:
> >
> > Yeah, when I hear complaints about all of my crap ^H^H^H er, *toys*,
> > I think about *these* sorts of things! :> The first friend (above)
> > gave me a 3KW FERRUPS (UPS) one day. I was trying to figure out how
> > to get it *into* the truck (weighed a couple hundred pounds... the
> > batteries alone weighed more than 100 pounds). He "disappeared".
> > And came back a few minutes later with a front-end loader, scooped
> > the UPS into the bucket and dropped it onto the truck.
> >
> > Sheesh!
>
> Indeed. :-) In my case it would still be in the truck.

You need one of these!

<http://www.harborfreight.com/1000-lb-capacity-hydraulic-scissor-table-cart-93116.html>

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

== 2 of 2 ==
Date: Sun, Jan 16 2011 7:21 am
From: "Michael A. Terrell"

David Nebenzahl wrote:
>
> On 1/15/2011 9:28 PM Michael A. Terrell spake thus:
>
> > Baron wrote:
> >>
> >> Very true ! A trick I've used to clean up the end of damaged bolts.
> >
> > How rebolting! ;-)
>
> Aaaaaah, the guy's nuts I say. Cross-threaded between the ears. Tapped
> out, ready to die.

Left hand thread in a right handed world!

--
You can't fix stupid. You can't even put a band-aid on it, because it's
Teflon coated.

==============================================================================
TOPIC: Magnifying glass for smd components
http://groups.google.com/group/sci.electronics.repair/t/152fab9f5593225c?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Jan 15 2011 6:01 pm
From: "Arfa Daily"

"Baron" <baron.nospam@linuxmaniac.nospam.net> wrote in message
news:igt358$gkj$2@news.eternal-september.org...
> D Yuniskis Inscribed thus:
>
>> On 1/15/2011 10:52 AM, Baron wrote:
>>> D Yuniskis Inscribed thus:
>>>> I have found that adequate *light* is more important than
>>>> magnification (but that may just be the age of my eyes)
>>>
>>> I can certainly empathise with that last paragraph. Good lighting is
>>> very important. Particularly where identifying colors is required.
>>
>> I find that I need more than "good" :-/
>>
>> I used to be able to read the markings on DIPs at arm's length
>> "with a glance". Now, I need to rock them back and forth to get
>> the light to reflect off them at the right angle before things
>> are visible (at times, I swear they have changed to BLACK INK!! :< )
>>
>> Ditto for color codes. Seems like the colors have crept closer
>> together in the spectrum :-/
>
> Yes colours have definitely become harder to read. I've used the "PTFE"
> tape trick on IC's and SMD parts a number of times to read the
> markings.
>
> --
> Best Regards:
> Baron.

But bear in mind what I said on here a few weeks ago about how hard it is to
distinguish similar coloured bands under CFL light, due to the hugely
discontinuous spectrum that the stupid things put out ...

Arfa

==============================================================================
TOPIC: Digital Volume Controls
http://groups.google.com/group/sci.electronics.repair/t/215bd1b40b7247b6?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Jan 16 2011 7:39 am
From: "Arfa Daily"

"William Brown" <wbrown@yahoo.com> wrote in message
news:vjk4j61b33us57aru9ivmjuts3e8nq4jcf@4ax.com...
>
>
> I was told to totally remove the grease as this has leaked out from the
> spindle, but not my theory.
>
>
> So is it OK for the contacts to run dry or should they be lubricated
> with CRC 2.26 or ELECTROLUBE EML.
>
>
> Thanks

It is very common for the 'stirring treacle' grease to migrate down the
spindle and onto the Gray disc and contacts in these rotary encoders, as
used as the volume control on many cheapo hifi units. I have restored more
of these than I care to remember over the years, by completely removing all
the grease from the disc and contacts. Before reassembling, I always add
just a little good quality (Electrolube in my case) contact cleaner /
lubricant, although strictly speaking, this should not be necessary, as both
the disc and the fixed contacts are usually gold plated. The success rate
and long-term refailure rate are excellent if you do a decent job, and it
doesn't take long.

Arfa

==============================================================================
TOPIC: OT--Actual electronics repair question
http://groups.google.com/group/sci.electronics.repair/t/1c7563aead5e20a6?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Jan 16 2011 10:33 am
From: Meat Plow

On Sun, 16 Jan 2011 00:25:40 -0500, Michael A. Terrell wrote:

> Meat Plow wrote:
>>
>> On Sat, 15 Jan 2011 13:25:29 -0800, Jeff Liebermann wrote:
>>
>> > On Sat, 15 Jan 2011 20:54:48 +0000 (UTC), Meat Plow
>> > <mhywatt@yahoo.com> wrote:
>> >
>> >>I think it stores in erasable prom but can't be sure. I had it open
>> >>once and don't recall seeing anything big enough to be a supercap or
>> >>battery. It's really miniaturized.
>> >
>> > I'm too lazy to dig out the schematic, but I guess(tm) it's NVRAM of
>> > some sort. I don't see a coin cell inside. Some inside photos:
>> > <http://www.mods.dk/picture.php?brandid=7&model=vx-5r> Registration
>> > required to see them full size.
>>
>> Yeah I got the schematic around somewhere, to lazy to dig it up.
>>
>> > Note the big white circle that is silk screen to the PCB. That's
>> > where the speaker magnet is positioned. I suspect that if you place
>> > some foam tape to put some pressure on the PCB, it might reduce the
>> > microphonics.
>>
>> I think i read that suggestion a long time ago too.
>>
>> > Also, two reasons it's only on 440Mhz. It might be a seperate VCO
>> > oscillator for each band, and the LO multiplier ratio is higher for
>> > 440 than for the other bands.
>>
>> Understood.
>>
>> > Incidentally, I sorta blundered across this BNC to SMA adapter made
>> > specifically for various Yaesu handhelds. Looks better than the
>> > easily broken adapters I've been using.
>> > <http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=350298285336>
>> > There a bunch of others with similar design available.
>>
>> Yeah I have a couple SMA - BNC adapters. Bought them at a ham fest a
>> good while back. If you are going to use the SMA with an external
>> antenna in your home or vehicle they make an adaptor with coax
>> inbetween connectors. I have one that has an SMA on one end, a couple
>> feet of very thing 50 ohm coax (not sure the number but it's half as
>> thin or more as RG58/U) and a SO239 on the other. Beats using a BNC -
>> SO239 adapter.
>
>
> RG-174?

Could have been. About the right diameter.

--
Live Fast, Die Young and Leave a Pretty Corpse

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

You received this message because you are subscribed to the Google Groups "sci.electronics.repair"
group.

To post to this group, visit http://groups.google.com/group/sci.electronics.repair?hl=en

To unsubscribe from this group, send email to sci.electronics.repair+unsubscribe@googlegroups.com

To change the way you get mail from this group, visit:
http://groups.google.com/group/sci.electronics.repair/subscribe?hl=en

To report abuse, send email explaining the problem to abuse@googlegroups.com

==============================================================================
Google Groups: http://groups.google.com/?hl=en

Electronics

sci.electronics.repair - 25 new messages in 9 topics - digest

No Response to "sci.electronics.repair - 25 new messages in 9 topics - digest"

Post a Comment

Blog Roll

Blog Archive