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

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Today's topics:

==============================================================================
TOPIC: Smoke detector testing
http://groups.google.com/group/sci.electronics.repair/t/6ef9dd7cb94ece9a?hl=en
==============================================================================

== 1 of 2 ==
Date: Tues, Oct 26 2010 11:35 am
From: D Yuniskis

Ron wrote:

[snip]

> Or you could just tie a bit of smouldering rope/rag/cigar/other
> combustible to the end of a long pole...

+42

== 2 of 2 ==
Date: Tues, Oct 26 2010 2:16 pm
From: whit3rd

On Oct 26, 8:34 am, klem kedidelhopper <captainvideo462...@gmail.com>
wrote:
> We do fire alarm system inspections. To test smoke detectors we use a
> spray can... high cathedral
> ceilings. ...
> the equipment which is needed to reach these detectors in the
> sanctuaries in both buildings will cost me over 400.00

So, how about a smoke candle stub in a wire-cage, and one of those
little RC helicopters?

Or a smoke-ring blower (takes an oatmeal can and a rubber-glove and
a bit of string) on a stick? You can aim the smoke-ring in still
air...

It doesn't have to be 'official' equipment, does it?

==============================================================================
TOPIC: SPAM - Here's the address to report Blogspot abuse
http://groups.google.com/group/sci.electronics.repair/t/cdeeadeedad3a65c?hl=en
==============================================================================

== 1 of 1 ==
Date: Tues, Oct 26 2010 11:46 am
From: JeffM

Muhammad Junaid Aslam wrote:
>ieeebooks.blogspot.com

Repeated abuse:
http://groups.google.com/groups/search?enc_author=w_VxVRYAAACZE6j6KQH57rVuYZtFXht4o4cocwWvDVg2RHsu8f1bCg&q=blogspot&scoring=d&num=100

To report Blogspot abuse:
http://www.google.com/support/blogger/bin/request.py?hl=en&contact_type=spam

==============================================================================
TOPIC: OT: Is this question too challenging for a BSEE graduate?
http://groups.google.com/group/sci.electronics.repair/t/31ba2b6a402a3720?hl=en
==============================================================================

== 1 of 12 ==
Date: Tues, Oct 26 2010 12:05 pm
From: John Fields

On Tue, 26 Oct 2010 11:18:58 -0700, David Nebenzahl
<nobody@but.us.chickens> wrote:

>On 10/26/2010 10:53 AM Joel Koltner spake thus:
>
>> At least when I took the appropriate course, it was only about a week or so
>> between "here's the absolutely ideal op-amp model and use these rules to
>> figure out the gain" and "here's a real-world op-amp with finite gain" and
>> then a few more days to "...and finite frequency response, and offset
>> voltages, etc." -- so you didn't have to feel uneasy about the initial
>> hand-waving for too long. :-)
>
>Yep. That stuff about the ideal op-amp--infinite gain, infinite input
>impedance, zero output impedance, bandwidth to the far edges of the
>electromagnetic spectrum--makes it sound like a perpetual-motion machine ...

---
David,

Did you get the article I posted for you?

---
JF

== 2 of 12 ==
Date: Tues, Oct 26 2010 12:52 pm
From: whit3rd

On Oct 25, 12:43 am, "William Sommerwerck"
<grizzledgee...@comcast.net> wrote:
> >> It is pretty easy if you know about how the op-amp
> >> will do whatever it can to make the voltage at pin 2
> >> the same as pin 1.
> > But is this really true? This sounds like it might be either
> > a gross oversimplification or a possible falsehood.
>
> No, it's fact. It is, as I said, /the/ fundamental principle of op-amp
> circuit design.

I'd say the fundamental principle is high gain DC-and-up
amplification; the
balance of input potentials is derived from this, and is, rather, a
productive approximation. Useful, yes, but not fundamental.

It's this kind of 'principle' you have to drop when something
more important calls for your attention.

== 3 of 12 ==
Date: Tues, Oct 26 2010 2:24 pm
From: "tm"

"David Nebenzahl" <nobody@but.us.chickens> wrote in message
news:4cc71c48$0$2445$822641b3@news.adtechcomputers.com...
> On 10/26/2010 9:57 AM tm spake thus:
>
>> <PlainBill47@yawho.com> wrote in message
>> news:nvudc65qpifjekd8bv7o0hr4grtc3slntk@4ax.com...
>>
>>> On Sun, 24 Oct 2010 21:14:00 -0400, "Michael A. Terrell"
>>> <mike.terrell@earthlink.net> wrote:
>>>
>>>> You 'program' it by changing reistors.
>>>
>>> No kidding? You replace a simple variable power resistor, which
>>> only requires a screw driver to change the resistance with three
>>> resistors, an op-amp (which requires a separate power supply), and
>>> a mosfet. To change the value of the virtual resistor you have to
>>> change a resistor?
>>>
>>> It would seem to me a potentiometer would improve usability
>>> greatly.
>>
>> Geese. It was just a quiz to see if an applicant understood how an opamp
>> works.
>
> Yabbut, it says right there on the diagram "programmable load". So is it
> or isn't it? To me, "programmable" means (or at least implies) changeable
> by changing voltages or some other electronic parameter, not by physically
> substituting components. Yes, a potentiometer would seem to be a better
> choice--even if it is "just a quiz".
>
>> BTW, you didn't get the job.
>
> I didn't want it anyway.
>

I was just pulling your chain. It was a shitty job anyway. Imagine working
for someone
that asked you that question on a job interview. I would more like to be
asked what
have I done that made someone some money. It's just business anyway.

== 4 of 12 ==
Date: Tues, Oct 26 2010 3:22 pm
From: "krw@att.bizzzzzzzzzzzz"

On Tue, 26 Oct 2010 11:18:58 -0700, David Nebenzahl <nobody@but.us.chickens>
wrote:

For many uses the idealized model works extremely well. It's kinda like the
ideal resistor; it doesn't really exist but for most problems reality is close
enough to practice that the difference doesn't matter.

== 5 of 12 ==
Date: Tues, Oct 26 2010 3:25 pm
From: "krw@att.bizzzzzzzzzzzz"

On Tue, 26 Oct 2010 10:53:32 -0700, "Joel Koltner"
<zapwireDASHgroups@yahoo.com> wrote:

>"David Nebenzahl" <nobody@but.us.chickens> wrote in message
>news:4cc67064$0$2444$822641b3@news.adtechcomputers.com...
>> What you might ought have said is that the *circuit*, including the feedback
>> loop, forces the inverting input to (virtually) the same voltage as the
>> noninverting input, right? The op amp, in and of itself, doesn't "do"
>> anything to (that is, out of) either input. It's only by virtue of the
>> feedback that this action occurs.
>
>Yes... and of course you have to get the feedback "right" as well (negative
>for the simple sorts of applications we're discussing here) -- the astute EE
>101 student will point out that using the rules about infinite input
>impedances and the inverting/non-inverting voltages being the same, you could
>swap the inverting and non-inverting inputs and everything should still work,
>yes?

Positive infinity is equal to negative infinity on your planet? ;-)

>At least when I took the appropriate course, it was only about a week or so
>between "here's the absolutely ideal op-amp model and use these rules to
>figure out the gain" and "here's a real-world op-amp with finite gain" and
>then a few more days to "...and finite frequency response, and offset
>voltages, etc." -- so you didn't have to feel uneasy about the initial
>hand-waving for too long. :-)

I don't think I ever took a formal class using opamps. I learned about them
in a "special problems" classes, first with (tube/servo-multiplier) analog
computers then the IC versions.

== 6 of 12 ==
Date: Tues, Oct 26 2010 4:20 pm
From: "Joel Koltner"

<krw@att.bizzzzzzzzzzzz> wrote in message
news:16lec65ml3jnmcetseu7ffp3ustlmtlupm@4ax.com...
> Positive infinity is equal to negative infinity on your planet? ;-)

Something like that...

Someone here once posted a link to a commercial op-amp data sheet (Maxim?)
where the example circuit had +/- swapped!

> I don't think I ever took a formal class using opamps. I learned about them
> in a "special problems" classes, first with (tube/servo-multiplier) analog
> computers then the IC versions.

At the U. of Wisc where I was, it was covered in the first real EE class you
took. It went something like... DC analysis (Ohm, Norton, Thevenin), All
About Phasors, Op-Amps, general AC circuit analysis, and finally RC/RL/RLC
circuits (although the letter "Q" never came up once -- that was for later).

The teacher was a very good teacher, although unfortunately his knowledge
didn't extend much outside of the textbook. Strangely, he was a full tenured
guy, whereas the much more "practical" fellow teaching the "Circuits You Might
Actually Find Yourself Building In The Real World" classes missed obtaining
tenure several times and eventually retired early.

I occasionally wonder whatever became of some of my old professors and
teachers; one looks at them so differently when you're in school than once
you've been out in the working world for awhile.

---Joel

== 7 of 12 ==
Date: Tues, Oct 26 2010 4:42 pm
From: brent

On Oct 26, 7:20 pm, "Joel Koltner" <zapwireDASHgro...@yahoo.com>
wrote:

> At the U. of Wisc where I was, it was covered in the first real EE class you
> took. It went something like... DC analysis (Ohm, Norton, Thevenin), All
> About Phasors, Op-Amps, general AC circuit analysis, and finally RC/RL/RLC
> circuits (although the letter "Q" never came up once -- that was for later).
>

Q is for Qan't Quite Qalculate the Quiirky parts of the Quantity
Qorrectly

== 8 of 12 ==
Date: Tues, Oct 26 2010 4:59 pm
From: "krw@att.bizzzzzzzzzzzz"

On Tue, 26 Oct 2010 16:20:42 -0700, "Joel Koltner"
<zapwireDASHgroups@yahoo.com> wrote:

><krw@att.bizzzzzzzzzzzz> wrote in message
>news:16lec65ml3jnmcetseu7ffp3ustlmtlupm@4ax.com...
>> Positive infinity is equal to negative infinity on your planet? ;-)
>
>Something like that...
>
>Someone here once posted a link to a commercial op-amp data sheet (Maxim?)
>where the example circuit had +/- swapped!

You trust the applications sections on datasheets?

>> I don't think I ever took a formal class using opamps. I learned about them
>> in a "special problems" classes, first with (tube/servo-multiplier) analog
>> computers then the IC versions.
>
>At the U. of Wisc where I was, it was covered in the first real EE class you
>took. It went something like... DC analysis (Ohm, Norton, Thevenin), All
>About Phasors, Op-Amps, general AC circuit analysis, and finally RC/RL/RLC
>circuits (although the letter "Q" never came up once -- that was for later).

I think I'm a little older than you. ;-) The 709 was available but very few
used them at the time. The first classes were just RLC circuits, no active
components at all.

>The teacher was a very good teacher, although unfortunately his knowledge
>didn't extend much outside of the textbook. Strangely, he was a full tenured
>guy, whereas the much more "practical" fellow teaching the "Circuits You Might
>Actually Find Yourself Building In The Real World" classes missed obtaining
>tenure several times and eventually retired early.

I had a great prof for my more advanced circuits classes. He was a full
professor, a friend of the family (my father was an EE prof), and my
(academic) boss when I was a tech. I also had him for well over 10% of my
credits (which wasn't supposed to happen). I took the "special problems"
classes (8 semester hours, IIRC, another no-no) with him, too.

He was a great guy, though not all liked him. He gave miserable exams, but
then curved them so simple mistakes weren't a disaster. He planned the exams
so he could finish them in an hour, so the average was 50-60. One transfer
student got pissed because he had an 80 on the first exam. He studied his ass
off for the second and got everything right. The prof *never* had a perfect
exam, so took a point off for penmanship. The guy went ballistic. ...much
too serious.

>I occasionally wonder whatever became of some of my old professors and
>teachers; one looks at them so differently when you're in school than once
>you've been out in the working world for awhile.

This prof retired and went became a lawyer for his second career. :-/

== 9 of 12 ==
Date: Tues, Oct 26 2010 6:50 pm
From: David Nebenzahl

On 10/26/2010 12:05 PM John Fields spake thus:

> On Tue, 26 Oct 2010 11:18:58 -0700, David Nebenzahl
> <nobody@but.us.chickens> wrote:
>
>> On 10/26/2010 10:53 AM Joel Koltner spake thus:
>>
>>> At least when I took the appropriate course, it was only about a
>>> week or so between "here's the absolutely ideal op-amp model and
>>> use these rules to figure out the gain" and "here's a real-world
>>> op-amp with finite gain" and then a few more days to "...and
>>> finite frequency response, and offset voltages, etc." -- so you
>>> didn't have to feel uneasy about the initial hand-waving for too
>>> long. :-)
>>
>> Yep. That stuff about the ideal op-amp--infinite gain, infinite
>> input impedance, zero output impedance, bandwidth to the far edges
>> of the electromagnetic spectrum--makes it sound like a
>> perpetual-motion machine ...
>
> David,
>
> Did you get the article I posted for you?

No; what article? (I take it this is the real John Fields, right?)

--
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.

- Comment from an article on Antiwar.com (http://antiwar.com)

== 10 of 12 ==
Date: Tues, Oct 26 2010 6:49 pm
From: "Michael A. Terrell"

PlainBill47@yawho.com wrote:
>
> On Sun, 24 Oct 2010 21:14:00 -0400, "Michael A. Terrell"
> <mike.terrell@earthlink.net> wrote:
>
> >
> >PlainBill47@yawho.com wrote:
> >>
> >> On Sat, 23 Oct 2010 13:05:23 -0700, "William Sommerwerck"
> >> <grizzledgeezer@comcast.net> wrote:
> >>
> >> >> Any electronics technician should be able to solve this
> >> >> by inspection; no calculator necessary. 3K/1k = x/40,
> >> >> therefore x= 120 ohms. Come up with more difficult ones
> >> >> next time.
> >> >
> >> >What do you mean by "inspection"? Are you applying a formula you memorized?
> >> >Or do you /understand/ what's involved?
> >> >Probably better than you do. The voltage across R1 is 1/4 of +VDC. An op-amp tries to force both inputs to the same voltage. Since it was stipulated the op-amp is a 'classic, ideal' op amp, we can assume it has none of the defects found in the real world. As a result the voltage across R3 will also be 1/4 of VDC. The only way that can happen is if the effective resistance of Q1 is 3 times the resistance of R3, or 120 ohms.
> >>
> >> NOW, what is less certain is the proper answer to the problem
> >> "Calculate the equivalent resistance of this programmable load."
> >> Given that R1, R2, and R3 are all part of the load, the proper answer
> >> to the original diagram is 153.846 ohms. Except that circuit does not
> >> show any evidence of being 'programmable'.
> >
> >
> > You 'program' it by changing reistors.
> No kidding? You replace a simple variable power resistor, which only
> requires a screw driver to change the resistance with three resistors,
> an op-amp (which requires a separate power supply), and a mosfet. To
> change the value of the virtual resistor you have to change a
> resistor?
>
> It would seem to me a potentiometer would improve usability greatly.

It would seem to me you aren't familiar with a customized BOM or
SIT. I worked with both in manufacturing.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

== 11 of 12 ==
Date: Tues, Oct 26 2010 7:01 pm
From: "Michael A. Terrell"

tm wrote:
>
> "David Nebenzahl" <nobody@but.us.chickens> wrote in message
> news:4cc71c48$0$2445$822641b3@news.adtechcomputers.com...
> > On 10/26/2010 9:57 AM tm spake thus:
> >
> >> <PlainBill47@yawho.com> wrote in message
> >> news:nvudc65qpifjekd8bv7o0hr4grtc3slntk@4ax.com...
> >>
> >>> On Sun, 24 Oct 2010 21:14:00 -0400, "Michael A. Terrell"
> >>> <mike.terrell@earthlink.net> wrote:
> >>>
> >>>> You 'program' it by changing reistors.
> >>>
> >>> No kidding? You replace a simple variable power resistor, which
> >>> only requires a screw driver to change the resistance with three
> >>> resistors, an op-amp (which requires a separate power supply), and
> >>> a mosfet. To change the value of the virtual resistor you have to
> >>> change a resistor?
> >>>
> >>> It would seem to me a potentiometer would improve usability
> >>> greatly.
> >>
> >> Geese. It was just a quiz to see if an applicant understood how an opamp
> >> works.
> >
> > Yabbut, it says right there on the diagram "programmable load". So is it
> > or isn't it? To me, "programmable" means (or at least implies) changeable
> > by changing voltages or some other electronic parameter, not by physically
> > substituting components. Yes, a potentiometer would seem to be a better
> > choice--even if it is "just a quiz".
> >
> >> BTW, you didn't get the job.
> >
> > I didn't want it anyway.
> >
>
> I was just pulling your chain. It was a shitty job anyway. Imagine working
> for someone
> that asked you that question on a job interview. I would more like to be
> asked what
> have I done that made someone some money. It's just business anyway.

Imagine the interview when a director of engineering asks "Can you
design an Op Amp" when applying for a job as a component engineer when
he meant, "Can you design a circuit using an op amp." A few days prior
to that he refused an ECO to correct a problem with an OpAmp that i had
submitted. Not because it was wrong, but because it was one of his
designs. I had to go to management to get it signed off.

How the same director of engineering giving a 'class' in the
lunchroom and using a microphone in his 'Power Point' presentation as a
video source for a telemetry system?

How about his proposed new inventory system that listed passive
components by their value. We had over a dozen 10K resistors in
inventory, but his system would have assigned a single part number to
all of them. The interview was over when I pointed out the flaws in his
system, nd his decision that there only be one stock number for an IC
available in different speeds, packages and multiple vendors.

--
Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

== 12 of 12 ==
Date: Tues, Oct 26 2010 7:19 pm
From: "tm"

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:3YSdndK57NrYGFrRnZ2dnUVZ_qWdnZ2d@earthlink.com...
>
> PlainBill47@yawho.com wrote:
>>
>> On Sun, 24 Oct 2010 21:14:00 -0400, "Michael A. Terrell"
>> <mike.terrell@earthlink.net> wrote:
>>
>> >
>> >PlainBill47@yawho.com wrote:
>> >>
>> >> On Sat, 23 Oct 2010 13:05:23 -0700, "William Sommerwerck"
>> >> <grizzledgeezer@comcast.net> wrote:
>> >>
>> >> >> Any electronics technician should be able to solve this
>> >> >> by inspection; no calculator necessary. 3K/1k = x/40,
>> >> >> therefore x= 120 ohms. Come up with more difficult ones
>> >> >> next time.
>> >> >
>> >> >What do you mean by "inspection"? Are you applying a formula you
>> >> >memorized?
>> >> >Or do you /understand/ what's involved?
>> >> >Probably better than you do. The voltage across R1 is 1/4 of +VDC.
>> >> >An op-amp tries to force both inputs to the same voltage. Since it
>> >> >was stipulated the op-amp is a 'classic, ideal' op amp, we can assume
>> >> >it has none of the defects found in the real world. As a result the
>> >> >voltage across R3 will also be 1/4 of VDC. The only way that can
>> >> >happen is if the effective resistance of Q1 is 3 times the resistance
>> >> >of R3, or 120 ohms.
>> >>
>> >> NOW, what is less certain is the proper answer to the problem
>> >> "Calculate the equivalent resistance of this programmable load."
>> >> Given that R1, R2, and R3 are all part of the load, the proper answer
>> >> to the original diagram is 153.846 ohms. Except that circuit does not
>> >> show any evidence of being 'programmable'.
>> >
>> >
>> > You 'program' it by changing reistors.
>> No kidding? You replace a simple variable power resistor, which only
>> requires a screw driver to change the resistance with three resistors,
>> an op-amp (which requires a separate power supply), and a mosfet. To
>> change the value of the virtual resistor you have to change a
>> resistor?
>>
>> It would seem to me a potentiometer would improve usability greatly.
>
>
> It would seem to me you aren't familiar with a customized BOM or
> SIT. I worked with both in manufacturing.
>

Ok, I get it now. It was for a cost plus government job.

==============================================================================
TOPIC: Panasonic Plasmas/LCDs of Past 5 years - "Volume Leveler" Function
http://groups.google.com/group/sci.electronics.repair/t/192fcec79e92313a?hl=en
==============================================================================

== 1 of 2 ==
Date: Tues, Oct 26 2010 2:15 pm
From: ChrisCoaster

On Oct 26, 1:32 pm, "Arfa Daily" <arfa.da...@ntlworld.com> wrote:

> By the looks of it, the volume leveler feature that you have does exactly
> the same, but the opposite way round (left to increase, right to decrease)
> to the feature on my TV, and perhaps with a slightly wider and asymmetric
> range.
>
> Arfa- Hide quoted text -
>
> - Show quoted text -
_________________________

Uhh, that's exactly what I stated on 10/25! If the value on the left
is "+3" as I remember and if the level on the right is "-10", it would
serve to suggest that moving the bar tot he left would increase, and
to the right would decrease.

In any case, from what I've picked up here, it seems that this is not
a simple "limiter", but a "trim" setting that allows you to set all
inputs so they are roughly the same volume when switching from one to
another. Switching from Cable > VCR > DVD > and back to Cable
should be less of a jarring(!) experience. :) Doing this by ear
might not be the most accurate way, as compared to using audio test
tones(pink noise) and a meter, but perhaps using the average cable
channel as a reference, you could set the inputs hosting your other
sources to match the volume of that channel. Am I in the ballpark on
this?

-ChrisCoaster

== 2 of 2 ==
Date: Tues, Oct 26 2010 2:20 pm
From: ChrisCoaster

On Oct 26, 1:54 pm, "Wild_Bill" <wb_wildb...@XSPAMyahoo.com> wrote:

>
> The obvious solution from a manufacturer's point of view would be that
> everyone needs multiple separate systems for various locations within a
> home.
>
> --
> Cheers,
> WB
____________________
I used to work as a AV Tech in a place like that - it's called a
conference center.

-CC

==============================================================================
TOPIC: Another reason to hate CFLs ...
http://groups.google.com/group/sci.electronics.repair/t/87ea27a2579f0316?hl=en
==============================================================================

== 1 of 1 ==
Date: Tues, Oct 26 2010 3:10 pm
From: ChrisCoaster

On Oct 24, 1:46 pm, David Sanders <sanders6...@bellsouth.net> wrote:

>
> But can it grow superb colas?
> --
>
> - Show quoted text -
______________________
That will be fine! :) :D LOL

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==============================================================================
TOPIC: Today's Odd 'un ...
http://groups.google.com/group/sci.electronics.repair/t/142b02de8c0e2045?hl=en
==============================================================================

== 1 of 4 ==
Date: Tues, Oct 26 2010 5:47 pm
From: "Arfa Daily"

Fosdex multi-tracker / mixer with HDD and CD drive landed on the bench with
the reported fault of "Won't power up. When it last did, smoked"

Once opened, the problem was immediately apparent in that every secondary
side electrolytic on its switchmode power supply, was bulging to a greater
or lesser degree, with a couple of them gone to the point of the top having
split, and spewed electrolyte - the ones behind the reported smoke, I would
guess.

Having noted all the values, I removed them all (13 in total !), in
readiness to do a blanket replacement. Just for sport, I decided to run the
ESR meter over them to see just how bad they were. And this is where it got
odd ...

A couple of them were well out of spec, as you would expect when confronted
by a bulging can, but for the most part, all of them had an acceptable ESR
figure, including the 'exploded' ones. So I got out the capacitance meter
and ran that over them all. This time, almost without exception, all were
low or very low in value, including the two split ones, which were the
better part of open circuit. This was all quite the contrary of what I had
expected. In many cases in the past, I have found electrolytics which
exhibited a very high ESR, but whose value was just about spot on. I don't
recall ever seeing it the other way round though, like this. It's actually
hard to see how a cap can exhibit a perfect ESR, and yet have a value that
has dropped to less than half its marked nominal.

And aside from this, how on earth can every secondary side cap fail in this
way, and all at about the same time? It's not as though most of them are
placed in the designers' favourite spot of next to a heatsink or power
resistor. Neither is the interior of the unit particularly compact. I
wouldn't have thought that the temperature inside the case would get much
above ambient. I can only assume that the caps that have been used, are
either very badly specced, or of extremely poor quality.

Arfa

== 2 of 4 ==
Date: Tues, Oct 26 2010 6:46 pm
From: "Mark Zacharias"

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
news:yEKxo.10232$oC4.8363@newsfe21.ams2...
> Fosdex multi-tracker / mixer with HDD and CD drive landed on the bench
> with the reported fault of "Won't power up. When it last did, smoked"
>
> Once opened, the problem was immediately apparent in that every secondary
> side electrolytic on its switchmode power supply, was bulging to a greater
> or lesser degree, with a couple of them gone to the point of the top
> having split, and spewed electrolyte - the ones behind the reported smoke,
> I would guess.
>
> Having noted all the values, I removed them all (13 in total !), in
> readiness to do a blanket replacement. Just for sport, I decided to run
> the ESR meter over them to see just how bad they were. And this is where
> it got odd ...
>
> A couple of them were well out of spec, as you would expect when
> confronted by a bulging can, but for the most part, all of them had an
> acceptable ESR figure, including the 'exploded' ones. So I got out the
> capacitance meter and ran that over them all. This time, almost without
> exception, all were low or very low in value, including the two split
> ones, which were the better part of open circuit. This was all quite the
> contrary of what I had expected. In many cases in the past, I have found
> electrolytics which exhibited a very high ESR, but whose value was just
> about spot on. I don't recall ever seeing it the other way round though,
> like this. It's actually hard to see how a cap can exhibit a perfect ESR,
> and yet have a value that has dropped to less than half its marked
> nominal.
>
> And aside from this, how on earth can every secondary side cap fail in
> this way, and all at about the same time? It's not as though most of them
> are placed in the designers' favourite spot of next to a heatsink or power
> resistor. Neither is the interior of the unit particularly compact. I
> wouldn't have thought that the temperature inside the case would get much
> above ambient. I can only assume that the caps that have been used, are
> either very badly specced, or of extremely poor quality.
>
> Arfa

One or two caps develop enough ESR to cause a regulation problem, duty cycle
increases to compensate for the "low" DC level, the actual DC runs away,
caps are exposed to over-voltage, then vent.

Just like old Panasonic VCR's. Often only one line 5 volt for example, is
monitored for regulation purposes.

Mark Z.

== 3 of 4 ==
Date: Tues, Oct 26 2010 6:23 pm
From: dplatt@radagast.org (Dave Platt)

In article <yEKxo.10232$oC4.8363@newsfe21.ams2>,
Arfa Daily <arfa.daily@ntlworld.com> wrote:

>And aside from this, how on earth can every secondary side cap fail in this
>way, and all at about the same time? It's not as though most of them are
>placed in the designers' favourite spot of next to a heatsink or power
>resistor. Neither is the interior of the unit particularly compact. I
>wouldn't have thought that the temperature inside the case would get much
>above ambient. I can only assume that the caps that have been used, are
>either very badly specced, or of extremely poor quality.

Any chance that an upstream failure exposed these caps to excessive
voltage? If the switch regulator's sensing feedback loop were to
fail, the switcher might have "stuck on", and ended up pumping the raw
incoming voltage into the secondary rails?

--
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!

== 4 of 4 ==
Date: Tues, Oct 26 2010 7:24 pm
From: "tm"

"Dave Platt" <dplatt@radagast.org> wrote in message
news:nhbkp7-f9s.ln1@radagast.org...
> In article <yEKxo.10232$oC4.8363@newsfe21.ams2>,
> Arfa Daily <arfa.daily@ntlworld.com> wrote:
>
>>And aside from this, how on earth can every secondary side cap fail in
>>this
>>way, and all at about the same time? It's not as though most of them are
>>placed in the designers' favourite spot of next to a heatsink or power
>>resistor. Neither is the interior of the unit particularly compact. I
>>wouldn't have thought that the temperature inside the case would get much
>>above ambient. I can only assume that the caps that have been used, are
>>either very badly specced, or of extremely poor quality.
>
> Any chance that an upstream failure exposed these caps to excessive
> voltage? If the switch regulator's sensing feedback loop were to
> fail, the switcher might have "stuck on", and ended up pumping the raw
> incoming voltage into the secondary rails?
>
> --

How about loss of a single diode, short or open and the resulting AC applied
to the caps.

==============================================================================
TOPIC: Riding an air bag
http://groups.google.com/group/sci.electronics.repair/t/0d8fff4e5e1ab554?hl=en
==============================================================================

== 1 of 1 ==
Date: Tues, Oct 26 2010 7:25 pm
From: RoadRunner

If you think that sitting on an air bag in an attempt to get airborne
might be a bad idea, you would be correct!

http://www.craigboyce.com/w/2010/10/riding-an-air-bag/

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