sci.electronics.repair@googlegroups.com

Today's topics:

* Tektronix 2215A worth repair? - 3 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/fc4cb167c05d84fd?hl=en
* Tektronix cross reference pdf for download - 10 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/7592e05bd6ba8c74?hl=en
* Thoughts on this little oddity, anyone ...? - 3 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/9f831e8e8fd1b96e?hl=en
* Hot electrolytics - 2 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/abec0b759dbe9370?hl=en
* Mixing 4 audio channels to 3? - 3 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/a9c921002b2ed750?hl=en
* What Are the Cylyndrical Objects You Often See on Audio, USB, etc, Cables? -
4 messages, 4 authors
http://groups.google.com/group/sci.electronics.repair/t/ab1226e8296518ed?hl=en

==============================================================================
TOPIC: Tektronix 2215A worth repair?
http://groups.google.com/group/sci.electronics.repair/t/fc4cb167c05d84fd?hl=en
==============================================================================

== 1 of 3 ==
Date: Wed, Nov 9 2011 12:27 am
From: "N_Cook"

Geoff <public@email.com> wrote in message
news:Xns9F97CA1381610Geoff@88.198.244.100...
> I have a tek 2215A CRO with following fault..
> Left side of trace has a ripple, about 1/2 division vert
> amplitude and about 25% of horizontal is affected.
> Both channels the same
> When vert offset is manually swept, the pattern of ripple
> changes, still both channels the same
> Timebase does not change shape or size of ripple
> ripple is 1/2 or 1 cycle but is like someone has put a magnet on
> the side of the tube.
> Changing attenuator makes no difference.
> Was OK a few months ago when last used
>
> If this is a tube fault, I will junk it, what do others think?

I would suspect something in the flyback suppression/blanking area

== 2 of 3 ==
Date: Wed, Nov 9 2011 6:48 am
From: Jim Yanik

"Mark Zacharias" <mark_zacharias@labolgcbs.net> wrote in
news:4eb9ea1f$0$28552$a8266bb1@newsreader.readnews.com:

> "Geoff" <public@email.com> wrote in message
> news:Xns9F97CA1381610Geoff@88.198.244.100...
>>I have a tek 2215A CRO with following fault..
>> Left side of trace has a ripple, about 1/2 division vert
>> amplitude and about 25% of horizontal is affected.
>> Both channels the same
>> When vert offset is manually swept, the pattern of ripple
>> changes, still both channels the same
>> Timebase does not change shape or size of ripple
>> ripple is 1/2 or 1 cycle but is like someone has put a magnet on
>> the side of the tube.

some CRTs had tiny magnets (0.1" dia.) glued on at the factory,for beam
alignment.
one could have come loose.

>> Changing attenuator makes no difference.
>> Was OK a few months ago when last used
>>
>> If this is a tube fault, I will junk it, what do others think?
>
>
> Always start with the power supply.

Yes,PS filter caps,and other decoupling caps on the boards are a problem in
aging scopes.
>
> Mark Z.
>
>

to check tube geometry,input a 6 div high signal with a fast rise time(like
a square wave or time marks),one cycle per division,and turn up intensity
to see the fast rise.
if the tube is bad,you'll see distorted lines.
the distortion remains in the same place as you move trace position
controls.

IMO,2215-series are good scopes,easy to repair.
I have a 2213,one that I built myself from boards discarded by other techs.
Scored a second-grade CRT from the head of CRT mfg,bought the little bits I
needed to finish the scope for about $20.

good analog scopes are hard to find these days.

--
Jim Yanik
jyanik
at
localnet
dot com

== 3 of 3 ==
Date: Wed, Nov 9 2011 9:55 am
From: Geo

On Tue, 8 Nov 2011 23:51:53 +0000 (UTC), Geoff <public@email.com>
wrote:

>I have a tek 2215A CRO with following fault..
>Left side of trace has a ripple, about 1/2 division vert
>amplitude and about 25% of horizontal is affected.
>Both channels the same
>When vert offset is manually swept, the pattern of ripple
>changes, still both channels the same

I don't know this scope but used to work on another manufacturer's
models.
On one in particular, you could sometimes see this fault - it got
worse as the y shift was changed. As I recall, the problem was
timebase ripple (after flyback) on the supply to one of the tube
accelerating electrodes. The effect was more noticable as the beam was
moved (y shift) nearer to the electrode. You would need a second
scope to probe the tube pins to confirm this.

==============================================================================
TOPIC: Tektronix cross reference pdf for download
http://groups.google.com/group/sci.electronics.repair/t/7592e05bd6ba8c74?hl=en
==============================================================================

== 1 of 10 ==
Date: Wed, Nov 9 2011 4:17 am
From: JW

A nice find for anyone repairing Tektronix equipment
Interesting as it's marked company confidential.

www.ko4bb.com/Manuals/Tektronix/Tektronix_-_Miscelaneous/Tektronix_Xref_sm.pdf

414 pages of data!

== 2 of 10 ==
Date: Wed, Nov 9 2011 5:19 am
From: Jeffrey Angus

On 11/9/2011 6:17 AM, JW wrote:
> A nice find for anyone repairing Tektronix equipment
> Interesting as it's marked company confidential.
>
> www.ko4bb.com/Manuals/Tektronix/Tektronix_-_Miscelaneous/Tektronix_Xref_sm.pdf
>
> 414 pages of data!

Thankies for that.

Anyone got the matching HP cross?

Jeff

--
"Everything from Crackers to Coffins"

== 3 of 10 ==
Date: Wed, Nov 9 2011 6:00 am
From: JW

On Wed, 09 Nov 2011 07:19:43 -0600 Jeffrey Angus <grendelair@aim.com>
wrote in Message id: <j9dulf$ao$1@dont-email.me>:

>On 11/9/2011 6:17 AM, JW wrote:
>> A nice find for anyone repairing Tektronix equipment
>> Interesting as it's marked company confidential.
>>
>> www.ko4bb.com/Manuals/Tektronix/Tektronix_-_Miscelaneous/Tektronix_Xref_sm.pdf
>>
>> 414 pages of data!
>
>
>Thankies for that.
>
>Anyone got the matching HP cross?

These have been around for awhile
http://www.sphere.bc.ca/test/hpparts.html#cross

The biggest one is this:
http://www.sphere.bc.ca/download/hp_xref-free.pdf

If anyone else has any others, I'd be interested.

== 4 of 10 ==
Date: Wed, Nov 9 2011 6:14 am
From: Jeffrey Angus

On 11/9/2011 8:00 AM, JW wrote:
> The biggest one is this:
> http://www.sphere.bc.ca/download/hp_xref-free.pdf

Again, thankies

Jeff-1.0

--
"Everything from Crackers to Coffins"

== 5 of 10 ==
Date: Wed, Nov 9 2011 6:47 am
From: Robert Macy

On Nov 9, 5:17 am, JW <n...@dev.null> wrote:
> A nice find for anyone repairing Tektronix equipment
> Interesting as it's marked company confidential.
>
> www.ko4bb.com/Manuals/Tektronix/Tektronix_-_Miscelaneous/Tektronix_Xr...
>
> 414 pages of data!

Would you send directly to me? The URL does NOT work.

== 6 of 10 ==
Date: Wed, Nov 9 2011 7:32 am
From: JW

On Wed, 9 Nov 2011 06:47:26 -0800 (PST) Robert Macy
<robert.a.macy@gmail.com> wrote in Message id:
<4c9be1de-aea8-402c-8ef1-a90521f03424@m7g2000vbc.googlegroups.com>:

>On Nov 9, 5:17 am, JW <n...@dev.null> wrote:
>> A nice find for anyone repairing Tektronix equipment
>> Interesting as it's marked company confidential.
>>
>> www.ko4bb.com/Manuals/Tektronix/Tektronix_-_Miscelaneous/Tektronix_Xr...
>>
>> 414 pages of data!
>
>Would you send directly to me? The URL does NOT work.

Probably because you're using Google Groups [spit], and it looks like it's
trimming the URL. It's 31MB, so it would be best to download yourself.

Go to www.ko4bb.com and navigate your way - Manuals, Tektronix,
Tektronix_-_Miscelaneous. The file is named Tektronix_Xref_sm.

== 7 of 10 ==
Date: Wed, Nov 9 2011 7:43 am
From: Jeffrey Angus

On 11/9/2011 9:32 AM, JW wrote:
> Probably because you're using Google Groups [spit], and it looks like it's
> trimming the URL. It's 31MB, so it would be best to download yourself.

I sent Bob email with the correct links, untrimmed, for both cross
references.

Jeff-1.0

--
"Everything from Crackers to Coffins"

== 8 of 10 ==
Date: Wed, Nov 9 2011 8:06 am
From: JW

On Wed, 09 Nov 2011 09:43:38 -0600 Jeffrey Angus <grendelair@aim.com>
wrote in Message id: <j9e739$oir$1@dont-email.me>:

>On 11/9/2011 9:32 AM, JW wrote:
>> Probably because you're using Google Groups [spit], and it looks like it's
>> trimming the URL. It's 31MB, so it would be best to download yourself.
>
>I sent Bob email with the correct links, untrimmed, for both cross
>references.
>
>Jeff-1.0

I hadn't thought of that. Duh. Thanks.

== 9 of 10 ==
Date: Wed, Nov 9 2011 9:47 am
From: Robert Macy

On Nov 9, 8:43 am, Jeffrey Angus <grendel...@aim.com> wrote:
> On 11/9/2011 9:32 AM, JW wrote:
>
> > Probably because you're using Google Groups [spit], and it looks like it's
> > trimming the URL. It's 31MB, so it would be best to download yourself.
>
> I sent Bob email with the correct links, untrimmed, for both cross
> references.
>
> Jeff-1.0
>
> --
> "Everything from Crackers to Coffins"

thanks

== 10 of 10 ==
Date: Wed, Nov 9 2011 9:50 am
From: Robert Macy

On Nov 9, 9:06 am, JW <n...@dev.null> wrote:
> On Wed, 09 Nov 2011 09:43:38 -0600 Jeffrey Angus <grendel...@aim.com>
> wrote in Message id: <j9e739$oi...@dont-email.me>:
>
> >On 11/9/2011 9:32 AM, JW wrote:
> >> Probably because you're using Google Groups [spit], and it looks like it's
> >> trimming the URL. It's 31MB, so it would be best to download yourself.
>
> >I sent Bob email with the correct links, untrimmed, for both cross
> >references.
>
> >Jeff-1.0
>
> I hadn't thought of that. Duh. Thanks.

is ok. when the 'redirect to ..." sentence came up, just before it
would disappear, I ctrl-c'd it onto Notepad, corrected it to a
reasonable looking URL, and tried again. That worked! Took from 8:14
to 10:43 to get it downloaded using dial up. But it IS a wealth of
information. Thank you for posting!

==============================================================================
TOPIC: Thoughts on this little oddity, anyone ...?
http://groups.google.com/group/sci.electronics.repair/t/9f831e8e8fd1b96e?hl=en
==============================================================================

== 1 of 3 ==
Date: Wed, Nov 9 2011 4:29 am
From: "Mark Zacharias"

"Cydrome Leader" <presence@MUNGEpanix.com> wrote in message
news:j9cvdo$9a4$1@reader1.panix.com...
> Arfa Daily <arfa.daily@ntlworld.com> wrote:
>>
>>
>> "Cydrome Leader" <presence@MUNGEpanix.com> wrote in message
>> news:j9aahv$k3m$1@reader1.panix.com...
>>> Arfa Daily <arfa.daily@ntlworld.com> wrote:
>>>> Had an Allen & Heath PA20-CP 2 x 500 watt powered mixer in today. Has
>>>> two
>>>> completely separate and identical power amps, one of which was running
>>>> very
>>>> hot very quickly. No schematics, but problem was quickly traced to an
>>>> open
>>>> circuit resistor, by comparison ohms checks between the two amps. In
>>>> order
>>>> to replace the resistor, it was necessary to remove the offending ("B")
>>>> power amp to get to the board underside. The power rails and ribbon
>>>> from
>>>> the
>>>> mixer desk section were on removable connectors, but the 4 pole speakon
>>>> connector was bolted to the rear panel and the wires were soldered
>>>> directly
>>>> to the board. When I came to unsolder these wires from the socket, I
>>>> noticed
>>>> that the "B" channel one was wired the opposite way round to the "A"
>>>> channel
>>>> one. I noted this down to check on later.
>>>>
>>>> When the amp was tested ok, I bolted it back in, and reconnected the
>>>> speakon
>>>> socket the same as it was when I unsoldered it. The wires lay exactly
>>>> where
>>>> they originally were, and looked absolutely factory-original, even down
>>>> to
>>>> the one which went to the uppermost connector tag, having a rubber
>>>> sleeve
>>>> on
>>>> it, exactly the same as on the "A" channel. Except the two channels
>>>> were
>>>> definitely wired arse-about-face to one another. On both channels'
>>>> speakons,
>>>> the "1-" and "2-" pins were linked, as were "1+" and "2+". But on
>>>> channel
>>>> "A" the ground wire was connected to the "+" pair, and on the "B"
>>>> channel,
>>>> the ground was on the "-" pair.
>>>>
>>>> I fired it up again, and put a sine wave in, then hooked up two
>>>> channels
>>>> of
>>>> my 'scope, one to the "A" output and one to the "B", both with the same
>>>> polarity, and was surprised to find that the two signals were
>>>> completely
>>>> anti-phase, which meant that with the reversed connections to the
>>>> speakon
>>>> sockets, they would be back in phase again to the outside world.
>>>>
>>>> I then went back to the power amps' front ends near where the ribbon
>>>> connector was, and found the same thing. At the same point on each amp,
>>>> the
>>>> signals were in opposite phase to one another. I then spotted three
>>>> little 3
>>>> pin header blocks, with one pin pair on each designated "B", and the
>>>> other
>>>> pair "A" and a little 1 or maybe an I next to the "A" in a sort of 'to
>>>> the
>>>> power of' position. On the B amp, these three jumpers were set to "B",
>>>> and
>>>> on the A amp they were set to "A", so clearly, these jumpers reverse
>>>> the
>>>> phase of the signal coming in from the desk section. The two amps then
>>>> process the signals in antiphase to one another right to the final
>>>> output,
>>>> where the 'correct' phase relationship is again restored, by wiring the
>>>> speakon connector 'wrongly'.
>>>>
>>>> I have puzzled over this, and can think of no good reason for doing it
>>>> that
>>>> way. I did wonder at one point if it was anything to do with being able
>>>> to
>>>> make the amps bridgeable, but I downloaded a copy of the user manual,
>>>> and
>>>> there is a dire warning paragraph towards the end, specifically saying
>>>> that
>>>> under no circumstances should any attempt be made to operate the amps
>>>> in
>>>> bridge. It also warns against making any connections between the two
>>>> amps
>>>> or
>>>> any speakers connected to them, although in actual fact, the 'ground'
>>>> side
>>>> of each output is truly ground, and is common to both amps, the whole
>>>> (dual)
>>>> power supply, and all metalwork.
>>>>
>>>> What am I missing here ? Not of any real consequence, as the unit is
>>>> mended
>>>> and back in its original condition, but for academic interest, it would
>>>> be
>>>> good to understand the designer's thinking.
>>>>
>>>> Arfa
>>>>
>>>
>>> are these amps run from one power supply?
>>
>> Sort of. It's one bloody great torroidal tranny, for sure, but it looked
>> as
>> though there was enough filter caps on the board for it to be otherwise
>> two
>> independant supplies. Certainly, two sets of + / - / gnd cables came out
>> of
>> the psu for the two amps, but I must admit that I did not look at its
>> design
>> closely enough to see if there was two sets of secondary windings, and
>> two
>> rectifiers. The ground was certainly common to both amps, and one leg of
>> the
>> output on each amp was that same ground.
>>
>> Arfa
>
> It looks like others answered what I sort of suspected where they wanted
> to try to balance out the + and - rails when the audio peaks. I've never
> actually seen this before though.
>
> That reminds me- does anybody unnderstood what Carver's "power steering"
> was supposed to be or mean in their amps?
>

Probably refers to "rail-switching" where higher voltage power supply rails
are switched in on demand. (during musical peaks).

Has several advantages including being able to get away with a smaller power
transformer and smaller heat sinks. Reduces power dissipation at idle and at
low power.

It's said that such amps can sound nasty - not sure I've ever noticed that.

Mark Z.

== 2 of 3 ==
Date: Wed, Nov 9 2011 9:47 am
From: Cydrome Leader

Phil Allison <phil_a@tpg.com.au> wrote:
>
> "Cydrome Leader"
>
>> That reminds me- does anybody unnderstood what Carver's "power steering"
>> was supposed to be or mean in their amps?
>
>
> ** Bob Carver was an expert at coming up with high falutin' names for
> various clever dodges he used to save weight and cost.
>
> His " Magnetic Field " amps were nothing of the kind. They simply employed
> a triac based voltage regulator in the AC supply to improve the regulation
> factor of a ridiculously small iron transformer.

Hmm, was anybody in the 70s not obsessed with triac pre-regulation in all
sorts of power supplies?

> In his M400 and PM-2 designs, these puny transformers would emit cracking
> noises and *smoke* if you ever bench tested them at rated power for more
> than 60 seconds. No thermal shut down was fitted to save the trannies
> either.

nice.

> From the blurbs on "Power Steering" it applies to 5.1 channel amps and
> allows one audio channel to dominate the load on PSU at any given time.
> Likely a simple boost inhibit circuit that allows the use of a puny AC
> transformer again.

I own an older 5 channel carver amp. I recall upon opening it that the
power supply seemed way small for the alleged rated power across all
channels. The manual said something about this power steering crap, but
the block schematic didn't show anything indicating it was anything other
than "you can overload a channel a little bit before it burns out or the
fuse blows." It seems ok as far as amps in the early surround sound era
were. My DVD+sound setup is straight from 1998 and is this complex mess of
stuff running into a technics decoder and from there there are 5 RCA
cables running to each channel on the carver amp. There's some goofy fiber
link between the DVD player and the technics thing. Prior to this, I had a
stack of multiple stereos running everything. For a crappy action movie
where everything explodes, balance doesn't really matter.

I'm not even sure how you'd do this these days if you didn't get one of
this does everything consumer amps.

== 3 of 3 ==
Date: Wed, Nov 9 2011 10:13 am
From: "Gareth Magennis"

>> That reminds me- does anybody unnderstood what Carver's "power steering"
>> was supposed to be or mean in their amps?
>>
>
>
> Probably refers to "rail-switching" where higher voltage power supply
> rails are switched in on demand. (during musical peaks).
>
> Has several advantages including being able to get away with a smaller
> power transformer and smaller heat sinks. Reduces power dissipation at
> idle and at low power.
>
> It's said that such amps can sound nasty - not sure I've ever noticed
> that.
>
> Mark Z.

The Carver PM1.5 had both the triac and inadequate transformer, and rail
switching. High rail was + and - 125v IIRC.

Gareth.

==============================================================================
TOPIC: Hot electrolytics
http://groups.google.com/group/sci.electronics.repair/t/abec0b759dbe9370?hl=en
==============================================================================

== 1 of 2 ==
Date: Wed, Nov 9 2011 4:46 am
From: "N_Cook"

Anyone idea of the temperature required to make the heatshrink label wrapper
of a small radial electro shrink down the cylinder, requiring stretching the
shrunk end, sliding over the rim, before sliding down the cylinder part. ?

== 2 of 2 ==
Date: Wed, Nov 9 2011 7:23 am
From: "N_Cook"

How much is down to conflict between power supply designer and EMC
compliance bod?
Designer: I want convection vent holes here, here and here, through the
shielding
EMC bod: No way, I can let you have a few holes here and thats your lot

Just repaired an LCD monitor, probably started failure with ESR'd caps then
ohmic zener and eventually blown backlight inverter pair of transistors and
blown fuse. Plenty of holes top, side and bottom of the shield on the
digital processing side but only holes at the top on the ps side. So air
comes in on the colder side at bottom rises to the top by about mid board
and little or no air traversing the hottest section, that whole section in a
dead-zone in more ways than one, brilliant

==============================================================================
TOPIC: Mixing 4 audio channels to 3?
http://groups.google.com/group/sci.electronics.repair/t/a9c921002b2ed750?hl=en
==============================================================================

== 1 of 3 ==
Date: Wed, Nov 9 2011 5:45 am
From: John Fields

On Tue, 8 Nov 2011 21:07:44 -0800, DaveC <invalid@invalid.net> wrote:

>Latest rev:
>
><http://i40.tinypic.com/35m026h.jpg>
>
>>> What needs to be reference to the new "ground"? Everything between the
>>> input
>>> caps and output caps?
>>
>> Pretty much... each of the op amps' noninverting inputs, and the
>> "bottom ends" of the potentiometers, as you have drawn them. *NOT*
>> the V- input to the op amp(s), of course.
>
>You do mean each of the op amps' *inverting* inputs, yes?

---
No.

Your drawing is wrong; signal goes to the inverting (-) inputs and the
Vcc/2 reference goes to the non-inverting (+) inputs.

--
JF

== 2 of 3 ==
Date: Wed, Nov 9 2011 9:07 am
From: DaveC

> Your drawing is wrong; signal goes to the inverting (-) inputs and the
> Vcc/2 reference goes to the non-inverting (+) inputs.
> JF

Thanks guys. Fixed:

<http://i44.tinypic.com/r1k8qa.jpg>

All else looks good?

Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
designs. Values for these?

Thanks.

== 3 of 3 ==
Date: Wed, Nov 9 2011 10:19 am
From: moroney@world.std.spaamtrap.com (Michael Moroney)

DaveC <invalid@invalid.net> writes:

>> Your drawing is wrong; signal goes to the inverting (-) inputs and the
>> Vcc/2 reference goes to the non-inverting (+) inputs.
>> JF

>Thanks guys. Fixed:

><http://i44.tinypic.com/r1k8qa.jpg>

>All else looks good?

You still have the signal go to the non-inverting input. The way the
schematic is, U1-U3 will throw their output hard to a rail or oscillate
with positive feedback from R13-R15.

>Are cap values reasonable? I added C8 & C9 out of habit of seeing in other
>designs. Values for these?

I worry that the RC time constant would have the reference be not at the
1/2 way point while C8 charges on powerup. I don't see a C9. Might do
something not so good to the subwoofer.

==============================================================================
TOPIC: What Are the Cylyndrical Objects You Often See on Audio, USB, etc,
Cables?
http://groups.google.com/group/sci.electronics.repair/t/ab1226e8296518ed?hl=en
==============================================================================

== 1 of 4 ==
Date: Wed, Nov 9 2011 7:32 am
From: Nelson

What are those cylindrical objects you often see surrounding the cable
on USB, Audio, Firewire, etc cables? I am assuming they are some kind
of passive RF interference filter. How do they work? How effective are
they?

I am having trouble with interference with an audio cable connected
from a computer to a TV and was wondering if a cable with one of these
doo-dads would be worth the $.

--
Nelson

== 2 of 4 ==
Date: Wed, Nov 9 2011 7:43 am
From: "petrus bitbyter"

"Nelson" <nelson@nowhere.com> schreef in bericht
news:0001HW.CAE0073A00514F8EB01029BF@news.astraweb.com...
> What are those cylindrical objects you often see surrounding the cable
> on USB, Audio, Firewire, etc cables? I am assuming they are some kind
> of passive RF interference filter. How do they work? How effective are
> they?
>
> I am having trouble with interference with an audio cable connected
> from a computer to a TV and was wondering if a cable with one of these
> doo-dads would be worth the $.
>
> --
> Nelson
>

They are ferrites and used for RF suppression. You can buy types that can be
clamped on existing cables and they usually are effective. Nor that
expensive too so it's worthwhile to give it a try.

petrus bitbyter

== 3 of 4 ==
Date: Wed, Nov 9 2011 7:44 am
From: Jeffrey Angus

On 11/9/2011 9:32 AM, Nelson wrote:
> What are those cylindrical objects you often see surrounding the cable
> on USB, Audio, Firewire, etc cables? I am assuming they are some kind
> of passive RF interference filter. How do they work? How effective are
> they?
>
> I am having trouble with interference with an audio cable connected
> from a computer to a TV and was wondering if a cable with one of these
> doo-dads would be worth the $.
>

Ferrite cores

Jeff

--
"Everything from Crackers to Coffins"

== 4 of 4 ==
Date: Wed, Nov 9 2011 9:10 am
From: Jeff Liebermann

On Wed, 9 Nov 2011 10:32:26 -0500, Nelson <nelson@nowhere.com> wrote:

>What are those cylindrical objects you often see surrounding the cable
>on USB, Audio, Firewire, etc cables?

Regulatory repellents. They're attached by the manufacturer to keep
the FCC off their back by limiting the amount of RFI/EMI sprayed by
their equipment.

>I am assuming they are some kind
>of passive RF interference filter.

Yep. Under the nearly impossible to remove plastic cover lies a heart
of powdered oxidized iron.

>How do they work?

Quite well. If an FCC Enforcement Burro inspector approached, all one
needs to do is wave the lumpy cable at the inspector, and he will
vanish into a smog of legalese.

>How effective are they?

100% successful. I haven't seen an FCC inspector for many years.

>I am having trouble with interference with an audio cable connected
>from a computer to a TV and was wondering if a cable with one of these
>doo-dads would be worth the $.

Oh well. You finally decided to disclose what you're trying to
accomplish, so I guess I'll have to provide a reasonable answer.

I assume the computah generated interference is trashing the picture
on the TV or is being heard on the TV audio. What channel is the TV
watching? If it's channel 3/4 from some kind of set top box, you
might find it more useful to simply avoid the RF problem and rewire
your TV setup to use a non-RF input. HDMI, DVI, component video,
S-video, and component video inputs should all be present on the back
of your unspecified model TV.

If you're only using the TV for computer audio, you could also
eliminate the problem by purchasing a set of "computah speakers" for
about $30. The speakers inside most TV's are fairly disgusting.

If none of these alternatives seem useful, you can purchase clamp on
ferrite filters.
<http://www.delevan.com/web/PDF/Suppressors/Cable/BFseries/Page%20118_120_BF.pdf>
Radio Shock carries some:
<http://www.radioshack.com/product/index.jsp?productId=3012599>
<http://www.radioshack.com/product/index.jsp?productId=2103222>
or you can just cannibalize the ferrite beads off an old cable. For
audio, just about anything will work. Bigger is better and running
multiple turns through the core is even better:
<http://www.stevelarkins.freeuk.com/computer_interference.htm>

Gotta run... good luck.

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

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