sci.electronics.repair@googlegroups.com

Today's topics:

* OT: Is this question too challenging for a BSEE graduate? - 6 messages, 6
authors
http://groups.google.com/group/sci.electronics.repair/t/31ba2b6a402a3720?hl=en
* Today's Odd 'un ... - 6 messages, 5 authors
http://groups.google.com/group/sci.electronics.repair/t/142b02de8c0e2045?hl=en
* Smoke detector testing - 4 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/6ef9dd7cb94ece9a?hl=en
* Panasonic Plasmas/LCDs of Past 5 years - "Volume Leveler" Function - 1
messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/192fcec79e92313a?hl=en
* How long do LED and/or LCD TVs last? - 5 messages, 4 authors
http://groups.google.com/group/sci.electronics.repair/t/05ceb00cb61af986?hl=en
* Sherwood RD6106 tuner amp, prob 2000 year - 2 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/6bd29a50c856b3cd?hl=en
* Cheap Wholesale Coach Handbags Chanel Handbags GUCCI Handbags (http://www.24
hoursneakers.com/) (PayPal Payment) - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/cfcc8156baf57505?hl=en

==============================================================================
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 6 ==
Date: Tues, Oct 26 2010 9:48 pm
From: "tm"

"Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
news:3sqdnbd75qeRNVrRnZ2dnUVZ_qWdnZ2d@earthlink.com...
>
> tm wrote:
>>
>> "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.
>
>
> No, you don't get it. Customized BOM allows lower costs by reusing
> most of a design for different customer needs. SIT (Select In Test)
> allows equipment to be built that exceeds the normal specifications of
> the current state of the art. HP and Tektronix used to do it in a lot
> of their products, as well. There was no 'cost plus' jobs for anyone.
> We would get a request for bid, or inquiry to see if we could supply
> what a customer needed. We would bid it, based on a current base model
> and all required customization to meet their needs. If they agreed to
> the price we built it and shipped it on schedule and on budget. It
> didn't matter who the customer was. NASA, NOAA, the ESA or numerous
> other customers in the Aerospace industry. Some of that equipment was
> in use 24/7 for over 30 years with no repairs.
>
> If you think that you can build state of the art microwave receivers
> with off the shelf parts, you need help.
>

I really do get it. I see you never worked on any "black" projects.

BOM and SIT are EE-101 so don't try to be so impressive with what you
think you know.

And by the way, I am not trying to piss you off. I was just trying to be a
bit sarcastic. By making a simple "resistor" using five parts and calling
it a "programmable" load sure sounds like someone was selling a design
at cost plus.

Regards (really),
tm

== 2 of 6 ==
Date: Wed, Oct 27 2010 2:45 am
From: John Fields

On Tue, 26 Oct 2010 18:50:13 -0700, David Nebenzahl
<nobody@but.us.chickens> wrote:

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

>>
>> Did you get the article I posted for you?
>
>No; what article? (I take it this is the real John Fields, right?)

---
Yeah. :-)

Here's the message ID:

68oac6du5ec8alsq27p63a3hehpdcdvn8q@4ax.com

If you can't get it let me know and I'll email you a copy.

---
JF

== 3 of 6 ==
Date: Wed, Oct 27 2010 7:44 am
From: "Michael A. Terrell"

tm wrote:
>
> "Michael A. Terrell" <mike.terrell@earthlink.net> wrote in message
> news:3sqdnbd75qeRNVrRnZ2dnUVZ_qWdnZ2d@earthlink.com...
> >
> > tm wrote:
> >>
> >> "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.
> >
> >
> > No, you don't get it. Customized BOM allows lower costs by reusing
> > most of a design for different customer needs. SIT (Select In Test)
> > allows equipment to be built that exceeds the normal specifications of
> > the current state of the art. HP and Tektronix used to do it in a lot
> > of their products, as well. There was no 'cost plus' jobs for anyone.
> > We would get a request for bid, or inquiry to see if we could supply
> > what a customer needed. We would bid it, based on a current base model
> > and all required customization to meet their needs. If they agreed to
> > the price we built it and shipped it on schedule and on budget. It
> > didn't matter who the customer was. NASA, NOAA, the ESA or numerous
> > other customers in the Aerospace industry. Some of that equipment was
> > in use 24/7 for over 30 years with no repairs.
> >
> > If you think that you can build state of the art microwave receivers
> > with off the shelf parts, you need help.
> >
>
> I really do get it. I see you never worked on any "black" projects.

Sigh.

> BOM and SIT are EE-101 so don't try to be so impressive with what you
> think you know.
>
> And by the way, I am not trying to piss you off. I was just trying to be a
> bit sarcastic. By making a simple "resistor" using five parts and calling
> it a "programmable" load sure sounds like someone was selling a design
> at cost plus.
>
> Regards (really),
> tm

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

== 4 of 6 ==
Date: Wed, Oct 27 2010 12:51 pm
From: "David"

Regarding the subject line: When I first read this question and
looked at the schematic, it was not clear to me what the
programmable load that was asked about actually was. If it was
the FET, that should have been stated. There were many responses
that treated the entire circuit as the 'programmable load' hence
the 'in parallel with 4K ohms' type of answers. Furthermore, if
we assume the question was about the FET being the load to
calculate, that resistance has a DC and AC component and they are
very different. A question like this is very poorly worded and
should in no way be a judge of the person attempting to answer
it.
David

== 5 of 6 ==
Date: Wed, Oct 27 2010 1:22 pm
From: ehsjr

David Nebenzahl wrote:
> On 10/26/2010 8:06 PM ehsjr spake thus:
>
>> David Nebenzahl wrote:
>>
>>> But just a small quibble with the way you and others have described
>>> what's going on here. You say "the op amp ... does whatever it can to
>>> make the - input the same voltage" (as the + input). In fact, it does
>>> no such thing: the input is, after all, just an input.
>>
>>
>> In fact, _it most certainly does_. Without external connection - the
>> feedback - it will fail to make the inputs equal. But it will do all
>> it can do until those voltages are equal.
>
>
> You mean the little op amp will huff and puff and turn blue? Not sure
> what you're getting at here. Without feedback, the inputs will simply be
> whatever they are.

Do you understand that the maximum output voltage that op amps
can produce differs between devices? Some go to the rail(s)
(or very close) and others go toward the rail(s) but can end up
well more than a volt away.

Assuming unequal input voltages:
If there is no feedback, the op amp responds to the unequal input
voltages and drives the output to whatever the maximum voltage is
for that specific op amp, in whichever direction the voltages on
the inputs dictate. It continues responding and driving forever,
or until the voltages are made equal by some external means.

If there is feedback, the output will go to whatever voltage
causes the input voltages to be equal, or will go to maximum
and keep on responding and driving the output to maximum if
the circuit feedback is insufficient to equalize the voltages.

In all cases, the op amp has done all that it can. In the first
case what it can do is limited by its maximum output voltage.
In the second case, where the feedback allows the voltages to become
equal, the op amp has done all that it can, because the equal
input voltages limit the Vout to the specific voltage that
creates equal inputs. In the third case, the op amp is once
again limited by whatever the maximum (or minimum) Vout it can
produce.

"An op amp does all that it can" does not mean or imply that it
somehow internally adjusts the input voltages. It can't do that.
It does what it _can_. It does everything that the inputs
allow and that the op amps own internal design allows.

I hope that clears it up for you. You're likely to encounter
the phrase again and again. It would seem that the smart course
is to try to understand it, rather than engage in what you termed
a semantic quibble.

Ed

>
>> You seem to have missed the fact that my entire post was discussing
>> feedback. Sigh.
>
>
> See the remainder of my reply that you posted below but didn't reply to.
>
>>> 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.
>
>
>

== 6 of 6 ==
Date: Wed, Oct 27 2010 2:42 pm
From: David Nebenzahl

On 10/27/2010 2:45 AM John Fields spake thus:

> On Tue, 26 Oct 2010 18:50:13 -0700, David Nebenzahl
> <nobody@but.us.chickens> wrote:
>
>> On 10/26/2010 12:05 PM John Fields spake thus:
>>
>>> Did you get the article I posted for you?
>>
>> No; what article? (I take it this is the real John Fields, right?)
>
> Yeah. :-)
>
> Here's the message ID:
>
> 68oac6du5ec8alsq27p63a3hehpdcdvn8q@4ax.com

Thunderbird knows not what to do with that address, just opens up a new
"compose" window.

> If you can't get it let me know and I'll email you a copy.

Thanks, but as you can see, my email address is (intentionally) munged.
Post it to web-space and give us a link?

Anyhow, thanks for the effort.

--
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)

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

== 1 of 6 ==
Date: Wed, Oct 27 2010 1:06 am
From: "Arfa Daily"

"Mark Zacharias" <mark_zacharias@sbcglobal.net> wrote in message
news:4cc7846b$0$863$c3e8da3$460562f1@news.astraweb.com...
> "Arfa Daily" <arfa.daily@ntlworld.com> wrote in message
> news:yEKxo.10232$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.

All good points from everyone. I will find out later today if any additional
probs, as I did not have enough 470uF caps in stock, so had to order some
more. I'm leaning towards Mark's theory, because I've seen it before now I
come to think about it, and interestingly, the caps that had failed most
badly, were a pair of parallelled 1200uF's on the main rail, which is
probably the one used as the reference for the control loop. If that is the
case, then here's hoping that the rest of the rails didn't go too wild
before it all fell over completely. I have seen downstream circuitry damaged
beyond sensible rescue, by this kind of failure in cheapo supermarket DVD
players employing really cheap and nasty power supplies ... :-\

I'll let y'all know ...

Arfa

== 2 of 6 ==
Date: Wed, Oct 27 2010 5:29 am
From: PeterD

On Tue, 26 Oct 2010 22:24:05 -0400, "tm"
<the_obamunist@whitehouse.gov> wrote:

>
>"Dave Platt" <dplatt@radagast.org> wrote in message
>news:nhbkp7-f9s.ln1@radagast.org...
>>...
>>
>> 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.
>

I'm reminded of the brain dead day I had a modem with a blown bridge
in the powersupply. Was four individual diodes, and I grabbed what I
thought were four standard Si diodes with the right current ratings.

To teach me to not think, fate substituted 5.1 volt zener diodes for
what I thought were rectifiers, and the results were, shall we say,
unexpected!

The only good thing was that once I replaced the zeners with regular
diodes, replaced the now blown regulator with a new one, it all came
back to life--but you can be sure I don't use poorly marked parts
without carefully checking to see what they are.

I have to agree, I think something other than just defective
capacitors is at work here--likely either an overvoltage or A/C is
getting into the caps and killing 'em.

== 3 of 6 ==
Date: Wed, Oct 27 2010 6:24 am
From: Meat Plow

On Tue, 26 Oct 2010 20:46:19 -0500, Mark Zacharias wrote:

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

Thanks for reminding me of those. Well not really thanks but more like
DAMMIT! Turned me off from Panasonic electronics for a long time.

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

== 4 of 6 ==
Date: Wed, Oct 27 2010 7:55 am
From: messineo

Arfa Daily <arfa.daily@ntlworld.com> wrote:
> 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 ...

I recently repaired a couple of powerline LAN adapters with about the same
defect, secondary SMPS electrolytics bulging (and SMPS not working anymore
however).
I always test for low ESR all electrolytics and all tested good, including
the bulging ones.
Replacing them however revived the SMPS.
I didn't test them for capacity, I just remember I was surprised by this
result.
Indeed the first time a bad electrolytic tests good with the ESR meter with
me.
I tend to believe the original capacitor were of very low quality (and/or
the design of the device was indeed bad) as both the units failed about
in the same week in their first summer of life (T > 30C here in the summer).

Regards

Frank IZ8DWF

== 5 of 6 ==
Date: Wed, Oct 27 2010 10:24 am
From: Jim Yanik

"Arfa Daily" <arfa.daily@ntlworld.com> wrote in
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
>
>

I had a TEK 1700 switcher supply that regulated on the +5V rail,and when
the +5V filter cap's ESR went high,the other rails drove up,for example the
+40 went to +63,and then the HV osc xstr running off the +40 began cooking
the PCB around it's leads until it because a short and caused the PS to
current limit(burst mode).Many of the secondary PS electrolytics were
cooked to some degree.

Some other TEK instruments had similar problems.(all switchers)

--
Jim Yanik
jyanik
at
localnet
dot com

== 6 of 6 ==
Date: Wed, Oct 27 2010 10:27 am
From: Jim Yanik

"tm" <the_obamunist@whitehouse.gov> wrote in
news:ia8267$id5$1@speranza.aioe.org:

>
> "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.
>
>

usually a shorted diode causes a current limit problem.
(burst,"click" or "chirp" mode)
I haven't seem many open secondary rect. diodes in switchers.

--
Jim Yanik
jyanik
at
localnet
dot com

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

== 1 of 4 ==
Date: Wed, Oct 27 2010 1:09 am
From: "N_Cook"

whit3rd <whit3rd@gmail.com> wrote in message
news:11a77ce7-5faa-46da-8094-551958686ce4@l17g2000yqe.googlegroups.com...
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?

*********

A lot of air movement with helicopter but I like the vortex generator idea.
Ascending to heaven in a stable interior environment should work very well,
those vortexes travel great distance before distorting or deviating

== 2 of 4 ==
Date: Wed, Oct 27 2010 6:35 am
From: "N_Cook"

Fix a cheapo laser pointer to the vortex barrel for sighting the target.
With cold smoke and barrel mounted vertically you are at an advantage being
able to let the smoke stabilise in the barrel before triggering, for very
symetrical and stable and far reaching smoke rings

== 3 of 4 ==
Date: Wed, Oct 27 2010 8:53 am
From: bud--

David Nebenzahl wrote:
>
> Have you ever been at the bottom of a 40-foot pole with a weight on the
> top, trying to guide it somewhere? It ain't easy.
>

I assume guiding the pole is the basic problem. The OP didn't say how
high the ceiling was, which might help.

I changed a 300W bulb about 40 ft up working from a tall step ladder
then using a standard light bulb changing pole and extensions. Three
light ropes were tied at the top to control where the bulb grabber went,
with 3 people on the ground guiding. After about 1 extension, you have
to guide the top as you add extensions. Working on a ladder allows
adding an extension under the stack. Extensions were around 8 or 10 ft.
You could probably kludge the extensions with 1/2 or 3/4" EMT and good
couplings.

== 4 of 4 ==
Date: Wed, Oct 27 2010 4:13 pm
From: David Nebenzahl

On 10/27/2010 6:35 AM N_Cook spake thus:

> Fix a cheapo laser pointer to the vortex barrel for sighting the target.
> With cold smoke and barrel mounted vertically you are at an advantage being
> able to let the smoke stabilise in the barrel before triggering, for very
> symetrical and stable and far reaching smoke rings

Smoke rings, you say?

Forget all these other ideas! Just get a man-lift and a cigar. Don't
have to go all the way "up to heaven", just far enough to get a nice big
fat smoke ring up to the detector.

--
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)

==============================================================================
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 1 ==
Date: Wed, Oct 27 2010 1:24 am
From: "Arfa Daily"

"ChrisCoaster" <ckozicki@snet.net> wrote in message
news:bf329110-fa89-495f-bf9c-0ddb59c937a6@30g2000yql.googlegroups.com...
> 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.

You have mis-read or mis-understood what I said in the section you have
snipped out. The point I was trying to make was that the *setting* was the
same as mine in principle if not in name and nuts and bolts functionality. I
was perfectly well aware of what you stated earlier, which is why I made
reference to it ...

>
> 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. :)

Why would you imagine it would be a 'limiter' ? The name they have given
it - as in "leveler" - is perfectly descriptive of its basic function.

>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
>

I dunno about in the ballpark. Standing on the pitcher's mound, I'd have
said. It really is a simple and straightforward feature, and I think you are
trying to introduce complexity into its use, that simply isn't there. It's
not a limiter, nor a dynamic compressor. It is, as you have arrived at, a
simple volume trim function that is individually assignable and savable to
every possible channel or AV source selection. Further, it is easily set by
ear, as we are not talking precision audio here. Perceived volume levels
change between individual programmes - hell, between individual *scenes*
even, sometimes - let alone between stations and inputs. Just pick an input,
pick a volume level that you like, and then use the feature on the ones that
don't match by default, to make them match by your reckoning. Simple.

Arfa

==============================================================================
TOPIC: How long do LED and/or LCD TVs last?
http://groups.google.com/group/sci.electronics.repair/t/05ceb00cb61af986?hl=en
==============================================================================

== 1 of 5 ==
Date: Wed, Oct 27 2010 6:04 am
From: Keith

All:
How old is your LED/LCD TV; and, does it still work as it did when you first bought it?

Keith

== 2 of 5 ==
Date: Wed, Oct 27 2010 6:30 am
From: Meat Plow

On Wed, 27 Oct 2010 13:04:00 +0000, Keith wrote:

> All:
> How old is your LED/LCD TV; and, does it still work as it did when you
> first bought it?
>
> Keith

The technology is only a couple years old.

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

== 3 of 5 ==
Date: Wed, Oct 27 2010 9:23 am
From: Jeff Liebermann

On Wed, 27 Oct 2010 13:04:00 +0000 (UTC), Keith
<keithdlee2000@gmail.com> wrote:

>All:
> How old is your LED/LCD TV; and, does it still work as it did when you first bought it?
>Keith

Most LED backlit TV manufacturers are claiming 100,000 hr lifetime.
<http://www.mimaki-ls.com/Pdf/appnote/AN-103%20LED%20Light%20Lifetime.pdf>
If you watch 8 hrs of TV per day, that's 12,500 days, or 34.2 years.
However, that rating is the time to where the brightness deteriorates
to *HALF* the original brightness. Methinks you will probably find it
irritating well before that point. At a 30% drop, my guess(tm) is
about 20,000 hrs or 6.8 years maximum before the wife and kids start
to complain.

The various color LED's deteriorate at different rates. In order for
LED illumination to work, the TV needs to have the combined color
balance continuously (dynamically) set to white, and will therefore
automagically compensate for any color drift due to aging. You will
probably notice some inconsistency in the background white level as
individual LED's age at different rates (heavily dependent on
temperature distribution).

It's far too soon to tell if the crystal ball gazers and number
jugglers are accurate for LED TV's. For practical purposes, assume
that the TV will last 1 day longer than the warranty period, that
overall quality will deteriorate as prices drop, and that repair parts
will be unobtainable when it finally fails.

--
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

== 4 of 5 ==
Date: Wed, Oct 27 2010 10:31 am
From: Jim Yanik

Jeff Liebermann <jeffl@cruzio.com> wrote in
news:ivigc61ckvo7972m1va032j9daqattrsms@4ax.com:

> On Wed, 27 Oct 2010 13:04:00 +0000 (UTC), Keith
><keithdlee2000@gmail.com> wrote:
>
>>All:
>> How old is your LED/LCD TV; and, does it still work as it did when
>> you first bought it?
>>Keith
>
> Most LED backlit TV manufacturers are claiming 100,000 hr lifetime.
><http://www.mimaki-ls.com/Pdf/appnote/AN-103%20LED%20Light%20Lifetime.pd
>f>
> If you watch 8 hrs of TV per day, that's 12,500 days, or 34.2 years.
> However, that rating is the time to where the brightness deteriorates
> to *HALF* the original brightness. Methinks you will probably find it
> irritating well before that point. At a 30% drop, my guess(tm) is
> about 20,000 hrs or 6.8 years maximum before the wife and kids start
> to complain.
>
> The various color LED's deteriorate at different rates. In order for
> LED illumination to work, the TV needs to have the combined color
> balance continuously (dynamically) set to white, and will therefore
> automagically compensate for any color drift due to aging. You will
> probably notice some inconsistency in the background white level as
> individual LED's age at different rates (heavily dependent on
> temperature distribution).

how does a TV "dynamically" set it's white balance?
>
> It's far too soon to tell if the crystal ball gazers and number
> jugglers are accurate for LED TV's. For practical purposes, assume
> that the TV will last 1 day longer than the warranty period, that
> overall quality will deteriorate as prices drop, and that repair parts
> will be unobtainable when it finally fails.
>
>
>

LCD TVs are the ones that won't last long;
the ones with fluorescent backlights using HV drivers.

--
Jim Yanik
jyanik
at
localnet
dot com

== 5 of 5 ==
Date: Wed, Oct 27 2010 1:08 pm
From: Jeff Liebermann

On Wed, 27 Oct 2010 12:31:31 -0500, Jim Yanik <jyanik@abuse.gov>
wrote:

More:
"How Long do LCD TVs Last?"
<http://lcdtvbuyingguide.com/lcdtv/lcdtv-lifetime.shtml>

"LED TV Technology Pros and Cons"
<http://www.lcdtvbuyingguide.com/led-tv/led-tv-pro-con.html>

>> The various color LED's deteriorate at different rates. In order for
>> LED illumination to work, the TV needs to have the combined color
>> balance continuously (dynamically) set to white, and will therefore
>> automagically compensate for any color drift due to aging. You will
>> probably notice some inconsistency in the background white level as
>> individual LED's age at different rates (heavily dependent on
>> temperature distribution).
>
>how does a TV "dynamically" set it's white balance?

I was told that with edge lit LED TV's, there are some photo
transistors scattered around the edge of the LCD along with the LED's.
Turn on each color in sequence, measure the light output, and adjust
the LED power to some desired reference. What I don't know is whether
the algorithm involves increasing the current to the low output LED,
which may cause a rather short lifetime, or whether it reduces the
current to all the other LED's, which will cause overall reduced white
output. I think the method is similar with back illuminated LED's
(local dimming), but I don't have any details. I presume that there
are patents on the topic, but I don't want to go digging right now.

OLED (organic LED) panels are the ones that worry me. They are known
to have a short lifetime (15,000 hrs to half brightness).

"LED TV Local Dimming Backlighting vs. LED TV Edge lit Backlighting;
Which is Better?"
<http://www.led-tvbuyingguide.com/ledtv/edge-light-vs-local-dimming.html>

>LCD TVs are the ones that won't last long;
>the ones with fluorescent backlights using HV drivers.

I see plenty of those panels in laptops using CCFL (cold cathode
fluorescent) tubes. Some brands die early, but most of what I've seen
lasts longer than the rest of the laptop. Unfortunately, perception
is everything, and the expected lifetime of a laptop is probably about
8 years. My guess(tm) is that the expected lifetime of the TV is much
longer. What I usually see in both laptops and TV's is a blown
backlighting HV inverter circuit or board. The CCFL tubes don't seem
to be a problem.

However, I wouldn't worry much about failure rate. LCD will be
obsolete once we get 3D projection TV as in Star Trek Holodeck.

--
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

==============================================================================
TOPIC: Sherwood RD6106 tuner amp, prob 2000 year
http://groups.google.com/group/sci.electronics.repair/t/6bd29a50c856b3cd?hl=en
==============================================================================

== 1 of 2 ==
Date: Wed, Oct 27 2010 8:34 am
From: "N_Cook"

I though that hygroscopic brown glue stuff went out in the 70s. Used to
secure 12.288M crystal for the digital interface processor was around and a
pin and had rusted through at the epoxy bond. Plenty of opportunity for
liquid to pass through top vents but no sign of liquid anywhere so
presumably this duff glue stuff again. Luckily easily replaced.
Unfortunately looks as thogh it was used as flip-chip temporary bonding
before soldering, hopefully away from anything rustable there.

Does anyone have a sure-fire way of dealing with delatching those white
nylon board spacer+pcb holders? Sometimes a banana plug/ wander plug cover
works, sometimes a small nut driver. So often in too awkward a place to get
pliers in at board level. One of these on this amp I ended up cutting one of
the pair of tangs off, to free the board. Perhaps a range of metal cylinders
with dowel handles, various bore sizes.

== 2 of 2 ==
Date: Wed, Oct 27 2010 1:41 pm
From: Cydrome Leader

N_Cook <diverse@tcp.co.uk> wrote:
> I though that hygroscopic brown glue stuff went out in the 70s. Used to
> secure 12.288M crystal for the digital interface processor was around and a
> pin and had rusted through at the epoxy bond. Plenty of opportunity for
> liquid to pass through top vents but no sign of liquid anywhere so
> presumably this duff glue stuff again. Luckily easily replaced.
> Unfortunately looks as thogh it was used as flip-chip temporary bonding
> before soldering, hopefully away from anything rustable there.
>
> Does anyone have a sure-fire way of dealing with delatching those white
> nylon board spacer+pcb holders? Sometimes a banana plug/ wander plug cover
> works, sometimes a small nut driver. So often in too awkward a place to get
> pliers in at board level. One of these on this amp I ended up cutting one of
> the pair of tangs off, to free the board. Perhaps a range of metal cylinders
> with dowel handles, various bore sizes.

If you have a pair of crappy needlenose pliers you don't love anymore you
can try to bend the tips inwards a bit. Those spacer things still suck,
especially when they're old and brittle and just break off.

==============================================================================
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http://groups.google.com/group/sci.electronics.repair/t/cfcc8156baf57505?hl=en
==============================================================================

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