sci.electronics.repair - 25 new messages in 7 topics - digest

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

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Today's topics:

* LM386 chip amp picks up radio interference. - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/809031519d942490?hl=en
* Really "need to" replace older CATV cables? Would my cableprovider really
filter my line against my will? - 2 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/31e43b6766887486?hl=en
* instructor's solutions manual for Engineering Circuit Analysis 7th Ed. by
William H. Hayt Jr - 1 messages, 1 author
http://groups.google.com/group/sci.electronics.repair/t/581816848dd6ea1f?hl=en
* A specific PCB bad practise, term for it ? - 3 messages, 2 authors
http://groups.google.com/group/sci.electronics.repair/t/8689adb4b80bfe29?hl=en
* Hi, WOuld some kind soul help me diagnose my switch mode power supplies? - 9
messages, 4 authors
http://groups.google.com/group/sci.electronics.repair/t/e0182493b4e28ce4?hl=en
* OT: Has anyone tried this product for heat-sink compound? - 6 messages, 4
authors
http://groups.google.com/group/sci.electronics.repair/t/6163429af05daf16?hl=en
* Challenge of Repairing vs Trashing - 3 messages, 3 authors
http://groups.google.com/group/sci.electronics.repair/t/3cd5c17c8ebe1b1c?hl=en

==============================================================================
TOPIC: LM386 chip amp picks up radio interference.
http://groups.google.com/group/sci.electronics.repair/t/809031519d942490?hl=en
==============================================================================

== 1 of 1 ==
Date: Sat, Apr 23 2011 10:00 pm
From: "Phil Allison"

"Father Haskell"
"Phil Allison"
> "Father Haskell"
>
>
> > Homemade, powered by small 13 vct transformer from an old
> > boom box and LM317T regulator (ps seems capable of 14v clean
> > power, easily). Sounds like it's picking up the nearest AM station,
> > especially loud and clear when I touch the volume and gain control
> > shafts. Touching the heat sink behind the 317 with a fingertip
> > _quiets_ the interference, though.
>
> ** Lemme guess - you have the IC in a plastic box with no shielding of any
> kind ?

Wooden box, open, power supply board and transformer laid
on workbench and connected with jumpers.

** RFI heaven.

Pun intended......

> Ideally, there needs to be a metal box that is connected to the negative
> supply, pin 4 of the IC plus the metal parts of any pots. Alternatively,
> connect the metal fames of each pot to the negative rail ( pin 4) and add
> a
> cap of about 2200pF across pins 2 and 4 to bypass radio frequency energy.

Easily fixed by covering the inside of the box with foil duct tape.

** Maybe so, but making reliable electrical connection to such foil is not
so easy.

Nuts, bolts and solder lugs are essential.

> The volume pot wiper needs to be de-coupled from pin 2 by a series
> combination of a 4.7 kohm resistor and a cap of about 0.1 uF. This stops
> DC
> voltage from pin 2 appearing on the pot and helps with RF suppression.
>
> http://www.national.com/ds/LM/LM386.pdf
>

http://fluxmonkey.com/electronoize/386amplifier.htm
modified by adding 25 ohm volume pot to the output end,
with the wiper connected to the speakers ( 2 x 3.3 ohm, series).

** I'd call that an output attenuator - not a " volume pot ".

..... Phil

==============================================================================
TOPIC: Really "need to" replace older CATV cables? Would my cableprovider
really filter my line against my will?
http://groups.google.com/group/sci.electronics.repair/t/31e43b6766887486?hl=en
==============================================================================

== 1 of 2 ==
Date: Sun, Apr 24 2011 1:19 am
From: "Michael A. Terrell"

Jreality wrote:
>
> The good news is that the modem has managed to remain online
> continuously ever since the technician left. So perhaps, for now,
> even though he is telling me I should replace the older cables,
> perhaps what he did improved the signal enough so that this modem can
> stay online. I got above 9 megabits per second downstream in a speed
> test last night, which isn't the fastest in the world, but it's triple
> the speed of DSL. If the outages happen again I can rule out the
> older CATV cables, by moving the modem to a newer line/jack, and then
> disconnecting the older cables from the system for a few days.

Who installed the original coax? If it was the builder or an
electrician, it will be the cheapest crap they could find, and was
intended for a MATV feed. Some was low grade RG-59 with a copper
braided shield that wasn't even good enough for the VHF channels.

> There already is an amplifier in the system. It was originally
> installed when a Cable modem couldn't work upstairs in my office when
> I first bought this place and had cable for a month or two. The amp
> was originally on the whole system, but my one Sci. Atlanta Box in the
> kitchen (actually a kitchen with a den area) eventually started
> getting interruptions, and I was told that the signal to the box was
> actually too strong so they added a splitter so that the signal going
> to that room isn't amplified.

The fact that you even need an amplifier indicates the coax is
defective or substandard.

> I'm still finding it a little "creepy" that I was being told by the
> technician that someone at the cable company can go around at my area
> and decide to slap a filter on my entire line at their green box, or
> slap a filter on a group of people's lines in my development without
> telling anyone. It seems to me that if they did that, then I should
> be able to move the modem to one of the newer CATV lines that were
> added after this place was built with a wireless router, and insist
> that they only slap filters on the older CATV cables as a solution
> rather than filtering out my whole system.

You don't know anything about how a CATV system works. Filters are
used on individual drops to block channels or groups of channels or
services that aren't paid for. There is supposed to be a small
directional coupler to split the cable modem form the TV feeds to drop
the level to what the modem needs, and reduce possible interference.

> They sent me a new modem because it's their policy of sending one to a
> new customer. The older modem is like 10 or more years old, and the
> speed I was getting wasn't as fast as a newer modem. If I could find
> out what frequency it uses, then maybe the new one could be "hacked"
> to use the same frequency as the older modem?

They all use the same frequencies for uploads and downloads. The
design of the newer modems allows a higher data rate. In fact, their
business customers can get a 40 Mb/S data rate if they want to pay for
it. Road Runner now offers it to residential customers in limited
areas. It all depends on how much spare fiber optics is available in
your area. Internet is carried over 'Fiber Enhanced Cable TV' which
means they use a piece of fiber optic cable for each area, then it is
converted to RF and connected to the system, for that limited area.

http://192.168.100.1/ will display the user interface on my S-A Cable
MODEM.

Name WebSTAR DPC2100R2
Modem Serial Number ********
Cable Modem MAC Address *****************
Hardware Version 2.1
Software Version v2.0.2r1256-060303
Receive Power Level -3.9 dBmV
Transmit Power Level 51.0 dBmV
Cable Modem Status Operational

> The reason I got Cable is because I have DSL too, and it was starting
> to really act up, and I got fed up. For the time being, DSL actually
> seems like it is back to being reliable. A major piece of equipment
> failed on their end that and they had to replace it. In my opinion it
> was acting up before it failed completely and causing some major DSL
> outages and some days of frequent intermittent outages before they
> fixed it. I signed up for Cable while DSL was troublesome, but Cable
> proved unreliable too, at least up until now. I'm gonna keep both
> for a while because I need a backup in case one has an outage. I
> may drop one of the two and get a mobile hotspot as a backup. Is
> Verizon any good for that?

DSL is a joke in most places. It is a low grade RF over a copper
pair system that uses old and failing copper telephone wire to deliver
the service. If you have the slightest problem with the pair, and it
fails.

> I won't tell you who my DSL provider is but lets just say the name
> begins with a V and ends in an n, and their DSL has had frustrating
> intermittant outages at times. Their tech support is not located in
> the US, and if you call them when there is an outage in your area, it
> can take several hours just for them to confirm you're not the only
> person having a connection problem, and they make you go through all
> kinds of steps on your end to try and rule out that it's your modem,
> etc.
>
> J.

--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

== 2 of 2 ==
Date: Sun, Apr 24 2011 1:33 am
From: "Michael A. Terrell"

Jeff Urban wrote:
>
> The problem could be standing waves. I don't think any FSM is accurate
> enough to detect that. First of all the cable modem requires a
> specific frequency, but it also requires the sidebands. In some cases
> standing waves can cause complete eradication of 400,0001 Mhz yet
> barely affect 400.0002 and 400.0000 Mhz. If this happens the signal
> strength is fine bit there is so much distortion in the modulation
> that the signal is near unusable.
>
> Remember reorienting the antenna to get rid of ghosts in a TV picture
> or distortion in an FM signal ? It is the same thing. Standing waves
> are very much like multipath in their effects on signal quality. Some
> old FM tuners actually had a scope built in to display multipath. The
> optimum signal would display pretty much a flat line. Moving the
> antenna would cause dips in the line, and that is what causes
> distortion. Measuring signal strength just doesn't cut it.
>
> He may have been blowing smoke about the TVs polluting the signal.

Ingression and radiation are continuing problems for CATV system
operators. The cause is two fold. Old or damaged cable, and tampering
or low grade work done by their customers. We used the 'Sniffer' brand
of monitors in our systems in all the service trucks to monitor the
system whenever they were on the road. The installers had to find a safe
place to pull over and call the dispatcher, to get the lead tech out to
find the source as soon as possible.

> It's hard to believe the effect would be a big problem if they meet
> FCC requirements on radiation. But then it's possible that he was just
> attempting to improve the signal as much as possible. Hard to say. I
> know people get alot of lip service when what they want is service,
> this one is tough to call either way. Maybe he just did what he
> could.
>
> But FCC requirements say nothing about antenna input impedance, if
> that is off it can cause the standing waves.

Sigh. By design the antennas used in CATV headends are all 75 ohms.
They aren't cheap radio Shack junk, but are single channel antennas made
for the CATV business. Some weigh in the hundreds of pounds and cost
several thousand dollars.

> I'm not sure if a filter
> would take care of that completely. It seems it should but I know
> better, things do not always work as they are supposed to.

Another know nothing answer. Filters have to be designed to work at
75 Ohms, or they don't work right.

> If you are talking a "thinner" cable than what is used tody it is
> probably RG59 or RG59U, both of which attenuate the high frequencies
> significantly. If the cables and the fittings are perfect this is
> simply due to capacitance and is not likely to cause standing waves.
> But then those things are not likely to be perfect, and may not have
> been in the beginning.
>
> The only way to tell really is with a sweep spectrum analyser, and
> those things will not be on the truck due to cost. The cables could
> also be checked for that using a time domain reflectometer, which
> would be even better, but look up the cost of one and you'll see why
> there was not one on the truck. It's simply too expensive.

Never heard of a TDR? CATV systems had a sweep test system for anual
'Proof Of Perfomance' testing at least back to the early '80s.

> It is possible that it is the cables, and you don't need a licensed
> electrician for that in most localities because there is no power
> involved. But finding someone who really knows how to hide the wires
> is not easy. Most higher caliber electricians can do it but they
> usually simply refuse because it is a ballbuster. I can do it, but
> unles you live nearby it is not going to happen.
>
> Do your neighbors have this problem ?

What difference does that make?

> If not get them to run a line
> straight into your existing cables and see if the problem persists.

How do you propose they make sure the signal levels are in the
required range for the cable MODEM?

> It
> will have to be attenuated to the same level you have now to make it a
> valid test.

It would make more sense for the CATV tech to swap ports on the line
tap, or just replace it.

> If it is found to be in the wiring in your unit, which can
> only be proven by others in the same complex using the same modem,
> with a couple of other requirements, it may be a matter of fishing a
> new cable into wherever it splits off into your unit. It is very hard
> to be absolutely sure, and the shotgun approach may be a better idea -
> which is to replace all the cables in your unit.

Sigh. Most in the wall wiring is done by idiots who staple it in
place. My crew had to bust a lot of drywall to replace bad coax, and a
lot was bad becasue 'Bozos 'R' Us' put a staple through the coax, inside
a wall.

> Now is another factor, there is more than one carrier frequency
> involved in cable internet distribution.

Really? Were in the DOCIS standard is this information?

> These two modems might work
> on different frequencies, and due to the nature of the effect of
> standing waves that can make all the difference in the world. So now
> the question is, since they got you hooked up with the other modem,
> why not just leave it that way ? Is there a rational explaination for
> that? They may have reasons we may never know, but it seems to me if
> they want that check every month they should do whatevwer it takes.

The average installer is clueless about cable MODEMs. Some can
barely do more than hook a TV to an existing drop. You need a lead
tech, or a cable internet trained tech.

> So my highly technical ass with all the experience has this advice -
> Tell them to take their service and shove it up where, well make sure
> it doesn't get a sunburn. Tell them the wires are fine with the old
> modem, why change it ? Tell them you are considering other options and
> since they can't provide what you are paying for the contract is null
> and void - they are in breach. You should see some action.
>
> See to them it's not just the monthly check, it's market share.
> Therefore threatening to quit works wonders. Got someone I know a free
> wireless router a few months ago, but she is sharp. Not when it comes
> to computers, but when it comes to money. She was head of the
> purchasing department before she retired and she gets things done.
> Threatening to do business elsewhere has alot more impact to companies
> like this than one might think. Having more customers does alot, it
> can affect stock prices, the D&B rating as well as their advetising
> plans. Use it against them if they don't deliver the goods.

--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

==============================================================================
TOPIC: instructor's solutions manual for Engineering Circuit Analysis 7th Ed.
by William H. Hayt Jr
http://groups.google.com/group/sci.electronics.repair/t/581816848dd6ea1f?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Apr 24 2011 1:22 am
From: ronald manual

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==============================================================================
TOPIC: A specific PCB bad practise, term for it ?
http://groups.google.com/group/sci.electronics.repair/t/8689adb4b80bfe29?hl=en
==============================================================================

== 1 of 3 ==
Date: Sun, Apr 24 2011 1:40 am
From: "Michael A. Terrell"

Smitty Two wrote:
>
> In article <iouqr0$pl0$1@dont-email.me>, "N_Cook" <diverse@tcp.co.uk>
> wrote:
>
> > Where holes are drilled for thru-board components but of diameter far too
> > big , thru-hole plated , but no eyelet/inserts used to fill the gap. So
> > 1N4001 size leads in holes twice their diameter and 1N4148 in holes twice
> > their diameter. So not a case of only one drill size for all. So in area
> > terms about 1 to 4 ratio of lead to solder. Bad enough practise with proper
> > solder but with PbF, ring cracks starting all over.
> > Is it to avoid mutiny by the by-hand board populators ?
>
> It's just careless design. As a contract assembly house, I see stuff
> like that all the time. Surface mount footprints the wrong size for the
> component, radial through holes for axial components, etc. ad infinitum.
> Quoted a one-off prototype board last week at 3 hours, took 17, due to
> documentation (and a slew of other) problems.
>
> EEs should be allowed a pencil and a paper napkin to sketch out the
> schematic, but after that, the board layout and overall product design
> should be turned over to someone who's actually familiar with
> manufacturing practices.

We had a board house add 'thermal rings' to the mounting holes in a
500 MHz synthesizer. It played hell with the modules and sent the phase
noise through the roof but they said that they would no longer make them
the way we needed them. it also dropped the center frequency by about
100 MHz. I had to take some of the copper foil we used to seal the
shields on the modules and cover them, then solder them to the surface
and the plated through holes, till we could get the boards from another
supplier. They routinely made a couple dozen different boards for us,
prior to that. When they decided to change our layouts without
permission, we dropped them.

--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

== 2 of 3 ==
Date: Sun, Apr 24 2011 1:43 am
From: "Michael A. Terrell"

Jim Yanik wrote:
>
> "N_Cook" <diverse@tcp.co.uk> wrote in news:iouqr0$pl0$1@dont-email.me:
>
> > Where holes are drilled for thru-board components but of diameter far
> > too big , thru-hole plated , but no eyelet/inserts used to fill the
> > gap. So 1N4001 size leads in holes twice their diameter and 1N4148 in
> > holes twice their diameter. So not a case of only one drill size for
> > all. So in area terms about 1 to 4 ratio of lead to solder. Bad
> > enough practise with proper solder but with PbF, ring cracks starting
> > all over. Is it to avoid mutiny by the by-hand board populators ?
> >
> >
> >
>
> perhaps PCBs designed for machine parts insertion have those sort of
> "oversize" thru-holes? Perhaps the insertion machine prefers big holes and
> besides,they crimp over the leads anyways.

Microdyne stopped bending the leads or using the special cutters that
cripmed the leads back in the '80s to reduced damage to the PTH.

> Maybe it's too much trouble to
> drill PCBs for different size thru-holes,and/or not worth the effort.

It's more likely that there was no design review, or the cad operator
was too lazy to verify the hole sizes.

> certainly stocking and inserting eyelets would be an additional,unnecessary
> expense.

--
You can't fix stupid. You can't even put a Band-Aid™ on it, because it's
Teflon coated.

== 3 of 3 ==
Date: Sun, Apr 24 2011 4:09 am
From: "N_Cook"

Michael A. Terrell <mike.terrell@earthlink.net> wrote in message
news:A8qdnSGUA-9Vfy7QnZ2dnUVZ_radnZ2d@earthlink.com...
>
> Jim Yanik wrote:
> >
> > "N_Cook" <diverse@tcp.co.uk> wrote in news:iouqr0$pl0$1@dont-email.me:
> >
> > > Where holes are drilled for thru-board components but of diameter far
> > > too big , thru-hole plated , but no eyelet/inserts used to fill the
> > > gap. So 1N4001 size leads in holes twice their diameter and 1N4148 in
> > > holes twice their diameter. So not a case of only one drill size for
> > > all. So in area terms about 1 to 4 ratio of lead to solder. Bad
> > > enough practise with proper solder but with PbF, ring cracks starting
> > > all over. Is it to avoid mutiny by the by-hand board populators ?
> > >
> > >
> > >
> >
> > perhaps PCBs designed for machine parts insertion have those sort of
> > "oversize" thru-holes? Perhaps the insertion machine prefers big holes
and
> > besides,they crimp over the leads anyways.
>
>
> Microdyne stopped bending the leads or using the special cutters that
> cripmed the leads back in the '80s to reduced damage to the PTH.
>
>
> > Maybe it's too much trouble to
> > drill PCBs for different size thru-holes,and/or not worth the effort.
>
>
> It's more likely that there was no design review, or the cad operator
> was too lazy to verify the hole sizes.
>
>
> > certainly stocking and inserting eyelets would be an
additional,unnecessary
> > expense.
>
>
> --
> You can't fix stupid. You can't even put a Band-AidT on it, because it's
> Teflon coated.

As the drill bits tend to be very brittle carbide rather than HSS I imagine
doubling the drill bit diameter drops the breakage rate by 1/10 or so,
reduced bit replacement costs, plus reduced down-time manual intervention
to rectify stoppages, due to such breakages.

==============================================================================
TOPIC: Hi, WOuld some kind soul help me diagnose my switch mode power supplies?

http://groups.google.com/group/sci.electronics.repair/t/e0182493b4e28ce4?hl=en
==============================================================================

== 1 of 9 ==
Date: Sun, Apr 24 2011 4:26 am
From: "Stephen"

Hi all,

I have three identical Headend UHF channelised amplifiers that all use
identical switch mode power supplies. One is working, the other two are
faulty but appear to have an identical fault as the output voltages are the
same low values on both units.

So I've got my screwdrivers out and a multimeter. Upon taking the backs of
all three units there is a 8 wire ribbon lead between the SMPS board and the
main board, comprising of 1 black wire and 7 grey ones.

There is a 8 wire ribbon cable that connects the SMPS to the main board,
which are the wire numbers in the middle of the image.

There are two columns of output voltages as tabulated below:

Probing for grounds and voltages gives me on both units:

Pin number Good unit 2 Bad Units
pin 1 ground ground (this has zero
resistance to the metal case)
pin 2 ground ground (this has zero
resistance to the metal case)
pin 3 -3.42v 0.4v
pin 4 0v 12.85v
pin 5 8.73v 0.76v
pin 6 18.32v 7.4v
pin 7 0v 8.8v
pin 8 0v 8.5v

There is approx 0.5Hz ripple on the secondary voltage outputs of the two
bad units and the green power indicating LED can be seen to ripple with the
naked eye..

None of the secondary side capacitors are bulging or have brown crud on them
and I'm already aware of the bad caps issue, so I replaced all the secondary
side electrolytics with Panasonic Low ESR FM series capacitors. This has not
made any difference.

I have traced the circuit schematic from the transformer to the output pins
of the SMPS board and the primary side from mains input to the transformer.
I don't know the exact winding configuration of the transformer, and I have
not yet traced the optoisolator board, but this is based on a 3 chip design,
TL400, CNY17 and UC3842AD, One is an opto isolator, one appears to be an
error amplifer/feedback chip and the third is a precision voltage reference.

I'd really appreciate some comment amongst any SMPS experts amongst you all
as to where the problem lies so I can get the two faulty units repaired.

The Primary side is available on
https://picasaweb.google.com/109749938109115860428/Apr242011?authkey=Gv1sRgCKzmsu6muqPFQA#5599104701271247186
and the numbers on the right refer to the pins on the transformer primary

The secondary side is available on
https://picasaweb.google.com/lh/photo/AHQo6tOf_NwmsTV_8owu9IbByfimUi_ZLKkVo27AQGI?feat=directlink
and the numbers on the left hand side refer to the order of connections on
the
transformer secondary

The whole of this side of the circuit is isolated from the primary side,
except for the one feedback wire off pins 1&2 which go off to an
optoisolator on a small daugherboard on the SMPS PCB.

Any comment?

Also there is a diode between two of the secondary windings that would seem
to short ciruit the winding back out onto itself? I have checked my PCB
tracing and its definately the case.

I'm of the view that the output of pin 4 should be 5 volts due to the
LM7805, so why is the working unit producing 8.73V at this point?

Give the 2.2K series resistor for the LED, and assuming a 10mA current, its
suggesting that the voltage coming out at this point should be 24.2 or is
there something subtle I'm missing? Also there are noi marked values for any
of the inductors.

Regards,

Stephen.

== 2 of 9 ==
Date: Sun, Apr 24 2011 5:26 am
From: "Uffe Bærentsen"

"Stephen" <i.want.spam@spam.com> skrev i en meddelelse
news:rtGdnTSRqdpvlSnQnZ2dnUVZ8tqdnZ2d@brightview.co.uk...

> Probing for grounds and voltages gives me on both units:
>
> Pin number Good unit 2 Bad Units
> pin 1 ground ground (this has zero
> resistance to the metal case)
> pin 2 ground ground (this has zero
> resistance to the metal case)
> pin 3 -3.42v 0.4v
> pin 4 0v 12.85v
> pin 5 8.73v 0.76v
> pin 6 18.32v 7.4v
> pin 7 0v 8.8v
> pin 8 0v 8.5v

What is these resistances:
pin 1 to pin 2
pin 1 to pin 4
pin 1 to pin 7
pin 1 to pin 8

I think you have an issue with the ground/0V.

--
Uffe Bærentsen

== 3 of 9 ==
Date: Sun, Apr 24 2011 7:01 am
From: "Stephen"

Would this be with the ribbon cable disconnected between the main board and
the PSU board?

If so which end should I measure?

"Uffe Bærentsen" <leiti_NOSPAM_@hotmail.com> wrote in message
news:4db41709$0$56778$edfadb0f@dtext02.news.tele.dk...
>
> "Stephen" <i.want.spam@spam.com> skrev i en meddelelse
> news:rtGdnTSRqdpvlSnQnZ2dnUVZ8tqdnZ2d@brightview.co.uk...
>
>> Probing for grounds and voltages gives me on both units:
>>
>> Pin number Good unit 2 Bad Units
>> pin 1 ground ground (this has zero
>> resistance to the metal case)
>> pin 2 ground ground (this has zero
>> resistance to the metal case)
>> pin 3 -3.42v 0.4v
>> pin 4 0v 12.85v
>> pin 5 8.73v 0.76v
>> pin 6 18.32v 7.4v
>> pin 7 0v 8.8v
>> pin 8 0v 8.5v
>
> What is these resistances:
> pin 1 to pin 2
> pin 1 to pin 4
> pin 1 to pin 7
> pin 1 to pin 8
>
> I think you have an issue with the ground/0V.
>
>
>
> --
> Uffe Bærentsen
>
>

== 4 of 9 ==
Date: Sun, Apr 24 2011 7:26 am
From: "Stephen"

"Stephen" <i.want.spam@spam.com> wrote in message
news:zdadnXF1H7GrsCnQnZ2dnUVZ8hWdnZ2d@brightview.co.uk...
> Would this be with the ribbon cable disconnected between the main board
> and the PSU board?
>
>>
With the ribbom cable disconnected, measuring at Main board end:
>> What is these resistances:
>> pin 1 to pin 2 0.05 ohms. this is as expected as pins 1 and 2 are
>> soldered together at the main board
>> pin 1 to pin 4 380kohm
>> pin 1 to pin 7 1.4 Mohm
>> pin 1 to pin 8 1.2 Mohm

With the ribbom cable disconnected, measuring at PSU board end:
>> What is these resistances:
>> pin 1 to pin 2 0.05 ohms. this is as expected as pins 1 and 2 are
>> soldered together at the PSU board
>> pin 1 to pin 4 180Kohm
>> pin 1 to pin 7 1 kohm
>> pin 1 to pin 8 1 kohm

With the ribbom cable CONNECTED, measuring on the ribbon cable:

>> What is these resistances:
>> pin 1 to pin 2 0.05 ohms. this is as expected as pins 1 and 2 are
>> soldered together at the main board
>> pin 1 to pin 4 340 kohm
>> pin 1 to pin 7 1 Kohm
>> pin 1 to pin 8 1 Kohm

All of the above readings are not steady, so I geuss there are capacitors
charging/discharging via the multimeter.

== 5 of 9 ==
Date: Sun, Apr 24 2011 7:44 am
From: "Wicaksono S."

This is a familiar error on UC384x based SMPS, 0.5 Hz ripple indicate
that the UC3842 is repeatedly goes on & off. There is an small
elecrolyte capacitor at UC3842 power supply pin that maybe went dry,
please replace it.

On Apr 24, 6:26 pm, "Stephen" <i.want.s...@spam.com> wrote:
> Hi all,
>
> I have three identical Headend UHF channelised amplifiers that all use
> identical switch mode power supplies. One is working, the other two are
> faulty but appear to have an identical fault as the output voltages are the
> same low values on both units.
>
> So I've got my screwdrivers out and a multimeter. Upon taking the backs of
> all three units there is a 8 wire ribbon lead between the SMPS board and the
> main board, comprising of 1 black wire and 7 grey ones.
>
> There is a 8 wire ribbon cable that connects the SMPS to the main board,
> which are the wire numbers in the middle of the image.
>
> There are two columns of output voltages as tabulated below:
>
> Probing for grounds and voltages gives me on both units:
>
> Pin number Good unit 2 Bad Units
> pin 1 ground ground (this has zero
> resistance to the metal case)
> pin 2 ground ground (this has zero
> resistance to the metal case)
> pin 3 -3.42v 0.4v
> pin 4 0v 12.85v
> pin 5 8.73v 0.76v
> pin 6 18.32v 7.4v
> pin 7 0v 8.8v
> pin 8 0v 8.5v
>
> There is approx 0.5Hz ripple on the secondary voltage outputs of the two
> bad units and the green power indicating LED can be seen to ripple with the
> naked eye..
>
> None of the secondary side capacitors are bulging or have brown crud on them
> and I'm already aware of the bad caps issue, so I replaced all the secondary
> side electrolytics with Panasonic Low ESR FM series capacitors. This has not
> made any difference.
>
> I have traced the circuit schematic from the transformer to the output pins
> of the SMPS board and the primary side from mains input to the transformer.
> I don't know the exact winding configuration of the transformer, and I have
> not yet traced the optoisolator board, but this is based on a 3 chip design,
> TL400, CNY17 and UC3842AD, One is an opto isolator, one appears to be an
> error amplifer/feedback chip and the third is a precision voltage reference.
>
> I'd really appreciate some comment amongst any SMPS experts amongst you all
> as to where the problem lies so I can get the two faulty units repaired.
>
> The Primary side is available onhttps://picasaweb.google.com/109749938109115860428/Apr242011?authkey=...
> and the numbers on the right refer to the pins on the transformer primary
>
> The secondary side is available onhttps://picasaweb.google.com/lh/photo/AHQo6tOf_NwmsTV_8owu9IbByfimUi_...
> and the numbers on the left hand side refer to the order of connections on
> the
> transformer secondary
>
> The whole of this side of the circuit is isolated from the primary side,
> except for the one feedback wire off pins 1&2 which go off to an
> optoisolator on a small daugherboard on the SMPS PCB.
>
> Any comment?
>
> Also there is a diode between two of the secondary windings that would seem
> to short ciruit the winding back out onto itself? I have checked my PCB
> tracing and its definately the case.
>
> I'm of the view that the output of pin 4 should be 5 volts due to the
> LM7805, so why is the working unit producing 8.73V at this point?
>
> Give the 2.2K series resistor for the LED, and assuming a 10mA current, its
> suggesting that the voltage coming out at this point should be 24.2 or is
> there something subtle I'm missing? Also there are noi marked values for any
> of the inductors.
>
> Regards,
>
> Stephen.

== 6 of 9 ==
Date: Sun, Apr 24 2011 8:14 am
From: "Stephen"

Do you mean the 22uF 50v capacitor that is on the area next to the
daugherboard? It is actually near to the connecting pins between the PSU
board and the daughterboard.

reason I ask is that there are no electrolytics at all on the daughterboard
which contains the UC384x, all there are is the three IC's and a load of
surface mount components?

Regards

Stephen.

"Wicaksono S." <w_saono@lycos.com> wrote in message
news:3efc4e2d-0c00-42b8-86b2-674cd04288db@w9g2000prg.googlegroups.com...
This is a familiar error on UC384x based SMPS, 0.5 Hz ripple indicate
that the UC3842 is repeatedly goes on & off. There is an small
elecrolyte capacitor at UC3842 power supply pin that maybe went dry,
please replace it.

On Apr 24, 6:26 pm, "Stephen" <i.want.s...@spam.com> wrote:
> Hi all,
>
> I have three identical Headend UHF channelised amplifiers that all use
> identical switch mode power supplies. One is working, the other two are
> faulty but appear to have an identical fault as the output voltages are
> the
> same low values on both units.
>
> So I've got my screwdrivers out and a multimeter. Upon taking the backs of
> all three units there is a 8 wire ribbon lead between the SMPS board and
> the
> main board, comprising of 1 black wire and 7 grey ones.
>
> There is a 8 wire ribbon cable that connects the SMPS to the main board,
> which are the wire numbers in the middle of the image.
>
> There are two columns of output voltages as tabulated below:
>
> Probing for grounds and voltages gives me on both units:
>
> Pin number Good unit 2 Bad Units
> pin 1 ground ground (this has zero
> resistance to the metal case)
> pin 2 ground ground (this has zero
> resistance to the metal case)
> pin 3 -3.42v 0.4v
> pin 4 0v 12.85v
> pin 5 8.73v 0.76v
> pin 6 18.32v 7.4v
> pin 7 0v 8.8v
> pin 8 0v 8.5v
>
> There is approx 0.5Hz ripple on the secondary voltage outputs of the two
> bad units and the green power indicating LED can be seen to ripple with
> the
> naked eye..
>
> None of the secondary side capacitors are bulging or have brown crud on
> them
> and I'm already aware of the bad caps issue, so I replaced all the
> secondary
> side electrolytics with Panasonic Low ESR FM series capacitors. This has
> not
> made any difference.
>
> I have traced the circuit schematic from the transformer to the output
> pins
> of the SMPS board and the primary side from mains input to the
> transformer.
> I don't know the exact winding configuration of the transformer, and I
> have
> not yet traced the optoisolator board, but this is based on a 3 chip
> design,
> TL400, CNY17 and UC3842AD, One is an opto isolator, one appears to be an
> error amplifer/feedback chip and the third is a precision voltage
> reference.
>
> I'd really appreciate some comment amongst any SMPS experts amongst you
> all
> as to where the problem lies so I can get the two faulty units repaired.
>
> The Primary side is available
> onhttps://picasaweb.google.com/109749938109115860428/Apr242011?authkey=...
> and the numbers on the right refer to the pins on the transformer primary
>
> The secondary side is available
> onhttps://picasaweb.google.com/lh/photo/AHQo6tOf_NwmsTV_8owu9IbByfimUi_...
> and the numbers on the left hand side refer to the order of connections on
> the
> transformer secondary
>
> The whole of this side of the circuit is isolated from the primary side,
> except for the one feedback wire off pins 1&2 which go off to an
> optoisolator on a small daugherboard on the SMPS PCB.
>
> Any comment?
>
> Also there is a diode between two of the secondary windings that would
> seem
> to short ciruit the winding back out onto itself? I have checked my PCB
> tracing and its definately the case.
>
> I'm of the view that the output of pin 4 should be 5 volts due to the
> LM7805, so why is the working unit producing 8.73V at this point?
>
> Give the 2.2K series resistor for the LED, and assuming a 10mA current,
> its
> suggesting that the voltage coming out at this point should be 24.2 or is
> there something subtle I'm missing? Also there are noi marked values for
> any
> of the inductors.
>
> Regards,
>
> Stephen.

== 7 of 9 ==
Date: Sun, Apr 24 2011 8:19 am
From: Kripton

agree with that ...
search for a small capacitor 10-47µF next to the uc3842 and change it...
regards,

On 2011-04-24 16:44:15 +0200, "Wicaksono S." <w_saono@lycos.com> said:

> This is a familiar error on UC384x based SMPS, 0.5 Hz ripple indicate
> that the UC3842 is repeatedly goes on & off. There is an small
> elecrolyte capacitor at UC3842 power supply pin that maybe went dry,
> please replace it.
>
> On Apr 24, 6:26 pm, "Stephen" <i.want.s...@spam.com> wrote:
>> Hi all,
>>
>> I have three identical Headend UHF channelised amplifiers that all use
>> identical switch mode power supplies. One is working, the other two are
>> faulty but appear to have an identical fault as the output voltages are t
> he
>> same low values on both units.
>>
>> So I've got my screwdrivers out and a multimeter. Upon taking the backs o
> f
>> all three units there is a 8 wire ribbon lead between the SMPS board and
> the
>> main board, comprising of 1 black wire and 7 grey ones.
>>
>> There is a 8 wire ribbon cable that connects the SMPS to the main board,
>> which are the wire numbers in the middle of the image.
>>
>> There are two columns of output voltages as tabulated below:
>>
>> Probing for grounds and voltages gives me on both units:
>>
>> Pin number Good unit 2 Bad
> Units
>> pin 1 ground
> ground (this has zero
>> resistance to the metal case)
>> pin 2 ground
> ground (this has zero
>> resistance to the metal case)
>> pin 3 -3.42v
> 0.4v
>> pin 4 0v
> 12.85v
>> pin 5 8.73v
> 0.76v
>> pin 6 18.32v
> 7.4v
>> pin 7 0v
> 8.8v
>> pin 8 0v
> 8.5v
>>
>> There is approx 0.5Hz ripple on the secondary voltage outputs of the t
> wo
>> bad units and the green power indicating LED can be seen to ripple with t
> he
>> naked eye..
>>
>> None of the secondary side capacitors are bulging or have brown crud on t
> hem
>> and I'm already aware of the bad caps issue, so I replaced all the second
> ary
>> side electrolytics with Panasonic Low ESR FM series capacitors. This has
> not
>> made any difference.
>>
>> I have traced the circuit schematic from the transformer to the output pi
> ns
>> of the SMPS board and the primary side from mains input to the transforme
> r.
>> I don't know the exact winding configuration of the transformer, and I
> have
>> not yet traced the optoisolator board, but this is based on a 3 chip desi
> gn,
>> TL400, CNY17 and UC3842AD, One is an opto isolator, one appears to be an
>> error amplifer/feedback chip and the third is a precision voltage referen
> ce.
>>
>> I'd really appreciate some comment amongst any SMPS experts amongst you a
> ll
>> as to where the problem lies so I can get the two faulty units repaired.
>>
>> The Primary side is available onhttps://picasaweb.google.com/109749938109
> 115860428/Apr242011?authkey=...
>> and the numbers on the right refer to the pins on the transformer primary
>>
>> The secondary side is available onhttps://picasaweb.google.com/lh/photo/A
> HQo6tOf_NwmsTV_8owu9IbByfimUi_...
>> and the numbers on the left hand side refer to the order of connections o
> n
>> the
>> transformer secondary
>>
>> The whole of this side of the circuit is isolated from the primary side,
>> except for the one feedback wire off pins 1&2 which go off to an
>> optoisolator on a small daugherboard on the SMPS PCB.
>>
>> Any comment?
>>
>> Also there is a diode between two of the secondary windings that would
> seem
>> to short ciruit the winding back out onto itself? I have checked my PCB
>> tracing and its definately the case.
>>
>> I'm of the view that the output of pin 4 should be 5 volts due to the
>> LM7805, so why is the working unit producing 8.73V at this point?
>>
>> Give the 2.2K series resistor for the LED, and assuming a 10mA current, i
> ts
>> suggesting that the voltage coming out at this point should be 24.2 or is
>> there something subtle I'm missing? Also there are noi marked values for
> any
>> of the inductors.
>>
>> Regards,
>>
>> Stephen.

--
---
Kripton

== 8 of 9 ==
Date: Sun, Apr 24 2011 8:22 am
From: Kripton

On 2011-04-24 13:26:49 +0200, "Stephen" <i.want.spam@spam.com> said:

> Hi all,
>
> I have three identical Headend UHF channelised amplifiers that all use
> identical switch mode power supplies. One is working, the other two are
> faulty but appear to have an identical fault as the output voltages are the
> same low values on both units.
>
> So I've got my screwdrivers out and a multimeter. Upon taking the backs of
> all three units there is a 8 wire ribbon lead between the SMPS board and the
> main board, comprising of 1 black wire and 7 grey ones.
>
> There is a 8 wire ribbon cable that connects the SMPS to the main board,
> which are the wire numbers in the middle of the image.
>
> There are two columns of output voltages as tabulated below:
>
> Probing for grounds and voltages gives me on both units:
>
> Pin number Good unit 2 Bad Units
> pin 1 ground ground (this has zero
> resistance to the metal case)
> pin 2 ground ground (this has zero
> resistance to the metal case)
> pin 3 -3.42v 0.4v
> pin 4 0v 12.85v
> pin 5 8.73v 0.76v
> pin 6 18.32v 7.4v
> pin 7 0v 8.8v
> pin 8 0v 8.5v
>
> There is approx 0.5Hz ripple on the secondary voltage outputs of the two
> bad units and the green power indicating LED can be seen to ripple with the
> naked eye..
>
> None of the secondary side capacitors are bulging or have brown crud on them
> and I'm already aware of the bad caps issue, so I replaced all the secondary
> side electrolytics with Panasonic Low ESR FM series capacitors. This has not
> made any difference.
>
> I have traced the circuit schematic from the transformer to the output pins
> of the SMPS board and the primary side from mains input to the transformer.
> I don't know the exact winding configuration of the transformer, and I have
> not yet traced the optoisolator board, but this is based on a 3 chip design,
> TL400, CNY17 and UC3842AD, One is an opto isolator, one appears to be an
> error amplifer/feedback chip and the third is a precision voltage reference.
>
> I'd really appreciate some comment amongst any SMPS experts amongst you all
> as to where the problem lies so I can get the two faulty units repaired.
>
> The Primary side is available on
> https://picasaweb.google.com/109749938109115860428/Apr242011?authkey=Gv1sRgCKzmsu6muqPFQA#5599104701271247186
and
>
> the numbers on the right refer to the pins on the transformer primary
>
> The secondary side is available on
> https://picasaweb.google.com/lh/photo/AHQo6tOf_NwmsTV_8owu9IbByfimUi_ZLKkVo27AQGI?feat=directlink
and
>
> the numbers on the left hand side refer to the order of connections on
> the
> transformer secondary
>
> The whole of this side of the circuit is isolated from the primary side,
> except for the one feedback wire off pins 1&2 which go off to an
> optoisolator on a small daugherboard on the SMPS PCB.
>
> Any comment?
>
> Also there is a diode between two of the secondary windings that would seem
> to short ciruit the winding back out onto itself? I have checked my PCB
> tracing and its definately the case.
>
> I'm of the view that the output of pin 4 should be 5 volts due to the
> LM7805, so why is the working unit producing 8.73V at this point?
>
> Give the 2.2K series resistor for the LED, and assuming a 10mA current, its
> suggesting that the voltage coming out at this point should be 24.2 or is
> there something subtle I'm missing? Also there are noi marked values for any
> of the inductors.
>
> Regards,
>
> Stephen.

you can make a quick esr analog meter to check all your caps
sure the small chemical capacitor next to the uc3842 is dry ...
my web site contains easy and more complex esr meter to build yourself
regards,

http://kripton2035.free.fr/esr-repository.html

--
---
Kripton

== 9 of 9 ==
Date: Sun, Apr 24 2011 8:44 am
From: "Stephen"

UPDATE: I have re-measured thge output voltages on the good working unit.

So here are the correct values:

> Probing for grounds and voltages gives me on both units:
>
> Pin number Good unit 2 Bad Units
> pin 1 ground ground pin 2
> ground ground
> pin 3 -3.42v -0.4v
> pin 4 30.2 12.85v
> pin 5 8.73v 0.76v
> pin 6 18.32v 7.4v
> pin 7 23.7v 8.8v
> pin 8 23.7v 8.5v

Also pins 7 & 8 are soldered together at the PSU end, pins 1 & 2 are
soldered toegether at both the PSU and the main board.

The UC3842AD, TL400 and the CNY17 are on a small daughterboard, which also
has a load of surface mount tantalum capacitors and resistors.

Asfar as electroyltics go, there is one on the main board, which is a capxon
22uF 50V job. is this likely to be the capacitor thats gone dry?

"Stephen" <i.want.spam@spam.com> wrote in message
news:rtGdnTSRqdpvlSnQnZ2dnUVZ8tqdnZ2d@brightview.co.uk...
> Hi all,
>
> I have three identical Headend UHF channelised amplifiers that all use
> identical switch mode power supplies. One is working, the other two are
> faulty but appear to have an identical fault as the output voltages are
> the same low values on both units.
>
> So I've got my screwdrivers out and a multimeter. Upon taking the backs of
> all three units there is a 8 wire ribbon lead between the SMPS board and
> the main board, comprising of 1 black wire and 7 grey ones.
>
> There is a 8 wire ribbon cable that connects the SMPS to the main board,
> which are the wire numbers in the middle of the image.
>
> There are two columns of output voltages as tabulated below:
>
> Probing for grounds and voltages gives me on both units:
>
> Pin number Good unit 2 Bad Units
> pin 1 ground ground (this has zero
> resistance to the metal case)
> pin 2 ground ground (this has zero
> resistance to the metal case)
> pin 3 -3.42v 0.4v
> pin 4 0v 12.85v
> pin 5 8.73v 0.76v
> pin 6 18.32v 7.4v
> pin 7 0v 8.8v
> pin 8 0v 8.5v
>
> There is approx 0.5Hz ripple on the secondary voltage outputs of the two
> bad units and the green power indicating LED can be seen to ripple with
> the naked eye..
>
> None of the secondary side capacitors are bulging or have brown crud on
> them and I'm already aware of the bad caps issue, so I replaced all the
> secondary side electrolytics with Panasonic Low ESR FM series capacitors.
> This has not made any difference.
>
> I have traced the circuit schematic from the transformer to the output
> pins
> of the SMPS board and the primary side from mains input to the
> transformer. I don't know the exact winding configuration of the
> transformer, and I have not yet traced the optoisolator board, but this is
> based on a 3 chip design, TL400, CNY17 and UC3842AD, One is an opto
> isolator, one appears to be an error amplifer/feedback chip and the third
> is a precision voltage reference.
>
> I'd really appreciate some comment amongst any SMPS experts amongst you
> all
> as to where the problem lies so I can get the two faulty units repaired.
>
> The Primary side is available on
> https://picasaweb.google.com/109749938109115860428/Apr242011?authkey=Gv1sRgCKzmsu6muqPFQA#5599104701271247186
> and the numbers on the right refer to the pins on the transformer primary
>
> The secondary side is available on
> https://picasaweb.google.com/lh/photo/AHQo6tOf_NwmsTV_8owu9IbByfimUi_ZLKkVo27AQGI?feat=directlink
> and the numbers on the left hand side refer to the order of connections on
> the
> transformer secondary
>
> The whole of this side of the circuit is isolated from the primary side,
> except for the one feedback wire off pins 1&2 which go off to an
> optoisolator on a small daugherboard on the SMPS PCB.
>
> Any comment?
>
> Also there is a diode between two of the secondary windings that would
> seem
> to short ciruit the winding back out onto itself? I have checked my PCB
> tracing and its definately the case.
>
> I'm of the view that the output of pin 4 should be 5 volts due to the
> LM7805, so why is the working unit producing 8.73V at this point?
>
> Give the 2.2K series resistor for the LED, and assuming a 10mA current,
> its
> suggesting that the voltage coming out at this point should be 24.2 or is
> there something subtle I'm missing? Also there are noi marked values for
> any
> of the inductors.
>
> Regards,
>
> Stephen.
>
>

==============================================================================
TOPIC: OT: Has anyone tried this product for heat-sink compound?
http://groups.google.com/group/sci.electronics.repair/t/6163429af05daf16?hl=en
==============================================================================

== 1 of 6 ==
Date: Sun, Apr 24 2011 6:22 am
From: Bob Villa

http://www.permatex.com/products/automotive/automotive_gasketing/gasket_makers/auto_permatex_ultra_copper_maximum_temperature_rtv_silicone_gasket_maker.htm

It would "seem" to have good properties for filling minute gaps;
copper for heat transfer; can't dry-out; not a bonding type on
silicone.

Thanks
bob_v

== 2 of 6 ==
Date: Sun, Apr 24 2011 6:48 am
From: "N_Cook"

Bob Villa <pheeh.zero@gmail.com> wrote in message
news:0a0e4aa2-74a4-4c20-bb66-5b2b021bec7f@u15g2000vby.googlegroups.com...
>
http://www.permatex.com/products/automotive/automotive_gasketing/gasket_make
rs/auto_permatex_ultra_copper_maximum_temperature_rtv_silicone_gasket_maker.
htm
>
> It would "seem" to have good properties for filling minute gaps;
> copper for heat transfer; can't dry-out; not a bonding type on
> silicone.
>
> Thanks
> bob_v

What is it like when it ends up on your clothing if assemblers use handfulls
of the stuff rather than ,all that is necessary, pin-head amounts. Let alone
large area bolted together Al to Al , H/S to chassis etc - can anyone
explain why its necessary there at all let alone handfulls of it

== 3 of 6 ==
Date: Sun, Apr 24 2011 7:22 am
From: Bob Villa

On Apr 24, 8:48 am, "N_Cook" <dive...@tcp.co.uk> wrote:
> Bob Villa <pheeh.z...@gmail.com> wrote in message
>
> news:0a0e4aa2-74a4-4c20-bb66-5b2b021bec7f@u15g2000vby.googlegroups.com...
>
> http://www.permatex.com/products/automotive/automotive_gasketing/gask...
> rs/auto_permatex_ultra_copper_maximum_temperature_rtv_silicone_gasket_maker.
> htm
>
>
>
> > It would "seem" to have good properties for filling minute gaps;
> > copper for heat transfer; can't dry-out; not a bonding type on
> > silicone.
>
> > Thanks
> > bob_v
>
> What is it like when it ends up on your clothing if assemblers use handfulls
> of the stuff rather than ,all that is necessary, pin-head amounts. Let alone
> large area bolted together Al to Al , H/S to chassis etc - can anyone
> explain why its necessary there at all let alone handfulls of it

It handles the same (consistency wise) as any thermal grease. It's gel-
like but "hardens" to a flexible but non-bonding constituent.

== 4 of 6 ==
Date: Sun, Apr 24 2011 9:00 am
From: Jeff Liebermann

On Sun, 24 Apr 2011 06:22:19 -0700 (PDT), Bob Villa
<pheeh.zero@gmail.com> wrote:

>http://www.permatex.com/products/automotive/automotive_gasketing/gasket_makers/auto_permatex_ultra_copper_maximum_temperature_rtv_silicone_gasket_maker.htm
>
>It would "seem" to have good properties for filling minute gaps;
>copper for heat transfer; can't dry-out; not a bonding type on
>silicone.

I've never tried it. However, looking at the MSDS sheet at:
<http://www.permatex.com/documents/msds/01_USA-English/81878.pdf>
there doesn't seem to be any copper in the mix. I can't even figure
out which of the ingredients give it the copper color. Also, the data
sheet includes all kinds of interesting characteristics, but
conveniently leaves out thermal conductivity.
<http://www.permatex.com/documents/tds/Automotive/81878.pdf>

Since 80% of the contents are silicon greases, and the rest is a mix
of silicon dioxide (ceramic) and mica, it would appear that the
thermal conductivity is primarily controlled by these additives. Both
are good thermal conductors, but in order to be really superior, the
flakes or gains need to touch and overlap in order to conduct the
heat. With less than 20% concentration, that's not going to happen.

Note the thermal conductivity of silicon grease as compared to various
metals, which are about 100 times more thermally conductive:
<http://upload.wikimedia.org/wikipedia/commons/1/1e/Thermal_conductivity.svg>
--
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

== 5 of 6 ==
Date: Sun, Apr 24 2011 10:12 am
From: Bob Villa

On Apr 24, 11:00 am, Jeff Liebermann <je...@cruzio.com> wrote:
> On Sun, 24 Apr 2011 06:22:19 -0700 (PDT), Bob Villa
>
> <pheeh.z...@gmail.com> wrote:
> >http://www.permatex.com/products/automotive/automotive_gasketing/gask...
>
> >It would "seem" to have good properties for filling minute gaps;
> >copper for heat transfer; can't dry-out; not a bonding type on
> >silicone.
>
> I've never tried it. However, looking at the MSDS sheet at:
> <http://www.permatex.com/documents/msds/01_USA-English/81878.pdf>
> there doesn't seem to be any copper in the mix. I can't even figure
> out which of the ingredients give it the copper color. Also, the data
> sheet includes all kinds of interesting characteristics, but
> conveniently leaves out thermal conductivity.
> <http://www.permatex.com/documents/tds/Automotive/81878.pdf>
>
> Since 80% of the contents are silicon greases, and the rest is a mix
> of silicon dioxide (ceramic) and mica, it would appear that the
> thermal conductivity is primarily controlled by these additives. Both
> are good thermal conductors, but in order to be really superior, the
> flakes or gains need to touch and overlap in order to conduct the
> heat. With less than 20% concentration, that's not going to happen.
>
> Note the thermal conductivity of silicon grease as compared to various
> metals, which are about 100 times more thermally conductive:
> <http://upload.wikimedia.org/wikipedia/commons/1/1e/Thermal_conductivi...>
> --
> Jeff Liebermann je...@cruzio.com
> 150 Felker St #D http://www.LearnByDestroying.com
> Santa Cruz CA 95060http://802.11junk.com
> Skype: JeffLiebermann AE6KS 831-336-2558

The reason I think it's a possible a good substitute is...it squeezes
down to an extremely thin film. If surfaces are nearly perfect...there
would be almost nothing between them.
Thanks for your input.

== 6 of 6 ==
Date: Sun, Apr 24 2011 10:43 am
From: boardjunkie1

On Apr 24, 2:22 pm, Bob Villa <pheeh.z...@gmail.com> wrote:
> http://www.permatex.com/products/automotive/automotive_gasketing/gask...
>
> It would "seem" to have good properties for filling minute gaps;
> copper for heat transfer; can't dry-out; not a bonding type on
> silicone.
>
> Thanks
> bob_v

Wow....really? You actually *want* to glue the parts to the heatsink?
Whatta mess that would make.

==============================================================================
TOPIC: Challenge of Repairing vs Trashing
http://groups.google.com/group/sci.electronics.repair/t/3cd5c17c8ebe1b1c?hl=en
==============================================================================

== 1 of 3 ==
Date: Sun, Apr 24 2011 8:56 am
From: Robert Macy

Have one of those small aluminum tube LED flashlights, approx 3 inch
long. During use on a cold night [40F], it suddenly started
flickering, rather than constantly on. After putting in a new battery,
the same.

Now no matter where even warm office, LED flashlight flickers.

Rate 'appears' to be 8-12/sec with a 70-30/80-20 ON cycle.

Any ideas if it's possible to fix?

== 2 of 3 ==
Date: Sun, Apr 24 2011 9:15 am
From: "Dave M"

Robert Macy wrote:
> Have one of those small aluminum tube LED flashlights, approx 3 inch
> long. During use on a cold night [40F], it suddenly started
> flickering, rather than constantly on. After putting in a new battery,
> the same.
>
> Now no matter where even warm office, LED flashlight flickers.
>
> Rate 'appears' to be 8-12/sec with a 70-30/80-20 ON cycle.
>
> Any ideas if it's possible to fix?

Therese things are so simple, it's almost embarrassing to ask how to fix
them. Temperature isn't the cause of the problem.
Most likely the on-off switch has pitted contacts. Disassemble the switch
and burnish of file the contacts until the pitting is gone.
Another possibility is that the switch contacts have lost "springiness" and
are barely making contact. Dissasemble the switch and bend them until there
is sufficient force to make firm contact.
If there is no switch (the head and the tube are screwed together to turn
the flashlight on), disassemble the flashlight and clean the dirt or other
stuff that's keeping the pieces from making good contact.
Last, see if the button of solder in the head that contacts the battery, has
taken a depression so that it's not making contact with the battery. If so,
put another good blob of solder on it to make vetter contact.
--
David
dgminala at mediacombb dot net

== 3 of 3 ==
Date: Sun, Apr 24 2011 10:23 am
From: nesesu

On Apr 24, 9:15 am, "Dave M" <dgminala4...@mediacombb.net> wrote:
> Robert Macy wrote:
> > Have one of those small aluminum tube LED flashlights, approx 3 inch
> > long. During use on a cold night [40F], it suddenly started
> > flickering, rather than constantly on. After putting in a new battery,
> > the same.
>
> > Now no matter where even warm office, LED flashlight flickers.
>
> > Rate 'appears' to be 8-12/sec with a 70-30/80-20 ON cycle.
>
> > Any ideas if it's possible to fix?
>
> Therese things are so simple, it's almost embarrassing to ask how to fix
> them. Temperature isn't the cause of the problem.
> Most likely the on-off switch has pitted contacts. Disassemble the switch
> and burnish of file the contacts until the pitting is gone.
> Another possibility is that the switch contacts have lost "springiness" and
> are barely making contact. Dissasemble the switch and bend them until there
> is sufficient force to make firm contact.
> If there is no switch (the head and the tube are screwed together to turn
> the flashlight on), disassemble the flashlight and clean the dirt or other
> stuff that's keeping the pieces from making good contact.
> Last, see if the button of solder in the head that contacts the battery, has
> taken a depression so that it's not making contact with the battery. If so,
> put another good blob of solder on it to make vetter contact.
> --
> David
> dgminala at mediacombb dot net

Not so sure about that. I have noticed that my cheap 3 LED flashlight
puts out a moderate RFI when on. Presumably there is a switcher of
some sort that ups the 1.4V from a single AA cell to run the 3 LEDs.
If the OP's one has asimilar switcher, it could have failed in the
cold [poor Pb free solder joint?] and remained faulty when warmed back
up again.

Neil S.

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