sci.electronics.repair - 21 new messages in 11 topics - digest

sci.electronics.repair
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Today's topics:

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TOPIC: hhhhhhhh
http://groups.google.com/group/sci.electronics.repair/t/9dd181d68284fd98?hl=en
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== 1 of 1 ==
Date: Sun, Apr 24 2011 2:24 pm
From: chabaan boussaid

hhhhhhh

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TOPIC: you need for Hardcover Mysteries
http://groups.google.com/group/sci.electronics.repair/t/ff9847587667f50e?hl=en
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== 1 of 1 ==
Date: Sun, Apr 24 2011 2:30 pm
From: chabaan boussaid

In 1964, D.C. socialite Mary Meyer was murdered. At the trial, the revelation of Mary's diary, which detailed an affair with President Kennedy, leads many to conspiracy theories and became the partial basis for Baldacci's best-seller, Absolute Power.

watch preview : http://amzn.to/e21nAH

tour review

==============================================================================
TOPIC: Mopar model 812 car radio, (early 1950's Chrysler product)
http://groups.google.com/group/sci.electronics.repair/t/3135639c17d6af1d?hl=en
==============================================================================

== 1 of 2 ==
Date: Sun, Apr 24 2011 4:00 pm
From: Meat Plow

On Sun, 24 Apr 2011 15:23:00 -0400, Michael A. Terrell wrote:

> Meat Plow wrote:
>>
>> On Sat, 23 Apr 2011 15:49:06 -0700, klem kedidelhopper wrote:
>>
>> > On Apr 20, 6:38Â pm, Meat Plow <mhywa...@yahoo.com> wrote:
>> >> On Wed, 20 Apr 2011 11:53:34 -0700, spamtrap1888 wrote:
>> >> > On Apr 20, 11:03Â am, PeterD <pet...@hipson.net> wrote:
>> >> >> On 4/20/2011 1:55 PM, Meat Plow wrote:
>> >>
>> >> >> > On Wed, 20 Apr 2011 05:29:17 -0700, klem kedidelhopper wrote:
>> >>
>> >> >> >> On Apr 20, 6:56 am, "Colin
>> >> >> >> Horsley"<horsley-s...@westnet.com.au> Â wrote:
>> >> >> >>> "klem kedidelhopper"<captainvideo462...@gmail.com> Â wrote in
>> >> >> >>> message
>> >>
>> >> >> >>> news:a5b8ddea-d0b2-40c4-b137-
>> >> >> > f151d4146...@r6g2000vbz.googlegroups.com...
>> >> >> >>> : It seems like everything coming in here lately is other
>> >> >> >>> than TV : repairs. But TV's are getting so cheap now and as a
>> >> >> >>> consequence things : are so slow I hate to turn anything away
>> >> >> >>> these days.This is a six volt : positive ground radio out of
>> >> >> >>> an early 1950's Chrysler product. Tubes : light up but
>> >> >> >>> vibrator will not buzz. I pulled the vibrator and : connected
>> >> >> >>> the coil terminals up to six volts and it does buzz. Not :
>> >> >> >>> conclusive but at the very least it tells me that six volts
>> >> >> >>> is not : reaching the coil. Does anyone have a schematic for
>> >> >> >>> this radio, or do : you know where I might find one? The
>> >> >> >>> owner just bought the car, is : restoring it and really wants
>> >> >> >>> to keep it original, so he'd really like : to have this radio
>> >> >> >>> working. Thanks, Lenny
>> >>
>> >> >> >>> Look here for your vibrator:-
>> >>
>> >> >> >>>http://www.radiosforoldcars.com/vibrators.htm
>> >>
>> >> >> >>> Colin in AUS
>> >>
>> >> >> >> Thanks for all the info guys.I don't know for certain yet if I
>> >> >> >> need a vibrator but I do need to order a schematic. Lenny
>> >>
>> >> >> > Pull the vibrator out of its case and look for welded contacts.
>> >> >> > Lots of times they can be separated and dressed with a relay
>> >> >> > file or fine emery nail file. Sometimes you can even bang on
>> >> >> > the vibrator and loosen the contacts if they aren't stuck
>> >> >> > together badly. I ran across this Youtube video some while
>> >> >> > back. It will help you immensly
>> >>
>> >> >> >http://youtu.be/Fp6PkRTmb8U
>> >>
>> >> >> yes, this can work. I've repaired a few over the years by
>> >> >> disassembling and using an auto points file on the contacts. They
>> >> >> are usually easy to take apart, too.
>> >>
>> >> > Guys, the OP says his vibrator buzzes when he applies 6 volts
>> >> > directly to it. That argues that the vibrator is not the problem,
>> >> > but that there's an open circuit between the power supply and the
>> >> > vibrator.
>> >>
>> >> > I would suspect that either the socket contacts or the pins on the
>> >> > vibrator are corroded.
>> >>
>> >> That's right, missed it. The video I posted can be used to
>> >> troubleshoot it further, the circuits are all pretty basic.
>> >>
>> >> --
>> >> Live Fast Die Young, Leave A Pretty Corpse
>> >
>> > Thanks everyone for the response I
>> > just came home from the hospital after having my hip replaced so I've
>> > been away from my repairs and this group for a few days. Lucky my
>> > shop is in my home so when I do feel like it I can try to get back to
>> > work. I did get the Sams from a guy in another group and I also got
>> > the vibrator to vibrate and the radio to work somewhat before I left.
>> > Possibly it was the rapping on the can that started it up. I also had
>> > some buzzing in the speaker and bridged an electrolytic across one of
>> > the terminals of the three section cap in the radio which improved
>> > it. So I'll replace that and possibly cut the vibrator open when I
>> > feel better. I remember doing that MANY years ago. Wow this thing
>> > draws 6.50 amps at 6,0 volts! I guess it HAS been a long
>> > time....Lenny -
>> > BTW thanks Meat Plow for the redirect to the video. It was a real
>> > good review.
>>
>> Make sure those suppressor caps on the vibrator are changed. Very
>> important not only for the life of the reed switches but also to
>> suppress EMI-RFI. Start with those and the power supply. Remember it's
>> 6 volts so it's going to appear to draw an unusual amount of current
>> over a 12 volt tube radio. Once you get the voltages up to snuff you
>> may want to tweak the receiver by disabling the 455khz osc (that thing
>> should have a superhet receiver) and insert a modulated tone signal of
>> 455khz at the (guessing here) G2 pin of the first tube in the line
>> through an .01 cap. Then a voltmeter at the output. Start with a
>> minimum reading on the VM then adjust the caps and IF cans for max.
>> Need a plastic hex tool for the cans they have two slugs, one for the
>> in and one for the out. Just some tips to spruce up that old goat.
>>
>> I've worked on my fair share of them back when you still found them on
>> cars driven every day.
>
>
> A lot of old car radios used a 262.5 KHz IF to prevent image problems
> at 910 KHz. 262.5 KHz puts them all out of band.

Old being before what year? I was just a young pup learning back in the
70's so I don't recall a 262 IF. Probably too much LSD later on.

--
Live Fast Die Young, Leave A Pretty Corpse

== 2 of 2 ==
Date: Sun, Apr 24 2011 8:44 pm
From: "Michael A. Terrell"

Meat Plow wrote:
>
> On Sun, 24 Apr 2011 15:23:00 -0400, Michael A. Terrell wrote:
> >
> > A lot of old car radios used a 262.5 KHz IF to prevent image problems
> > at 910 KHz. 262.5 KHz puts them all out of band.
>
> Old being before what year? I was just a young pup learning back in the
> 70's so I don't recall a 262 IF. Probably too much LSD later on.

Delco was still using 262.5 in the early '70s. I could repair most
of their mid '60s to mid '70s AM radios in less than 15 minutes. Some
took less than 5 minutes. I still hve most of the H.W. Sams AR series
manuals. The cheap Japanese radios used either 450 or 455 KHz IFs,
which caused problems on 900 or 910 KHz.

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

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

== 1 of 2 ==
Date: Sun, Apr 24 2011 4:46 pm
From: Father Haskell

On Apr 24, 1:00 am, "Phil Allison" <phi...@tpg.com.au> wrote:
> "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.

8 x 1 sheet metal screw with wire end bent 180 and clamped
between two washers.

>
> > 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

So you control volume by controlling input?

== 2 of 2 ==
Date: Sun, Apr 24 2011 5:51 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.

8 x 1 sheet metal screw with wire end bent 180 and clamped
between two washers.

So you control volume by controlling input?

** You after help is just like picking fights ?

Cos you are being damn rude.

.... Phil

==============================================================================
TOPIC: Are you getting bored...............so try it...............its Amazing.
..................
http://groups.google.com/group/sci.electronics.repair/t/1a2f9f7fcf654dc9?hl=en
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== 1 of 1 ==
Date: Sun, Apr 24 2011 4:54 pm
From: "N.SAMEENA BEGUM"

http://123maza.com/65/yours67/

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TOPIC: Annoying Clock on Microwave
http://groups.google.com/group/sci.electronics.repair/t/408849711f765a28?hl=en
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== 1 of 4 ==
Date: Sun, Apr 24 2011 5:09 pm
From: KR

On Apr 23, 5:36 am, "William Sommerwerck" <grizzledgee...@comcast.net>
wrote:
> > The only reason I can guess for the poor timekeeping is that the
> > circuitry/board running the clock is used on their 220 volt 50 Hz
> > versions without modification, so the makers decided not to use
> > line sync for the clock, and probably didn't want to spring for
> > a crystal oscillator either, so used an RC one instead.
>
> A chip would likely be designed to work at either frequency, with a jumper
> making the selection.

IF it is set to 50HZ and you are on a 60HZ supply - then it would run
faster, not slower.

Open it up and see if there is some sort of trimmer capacitor there
near the clock chip, adjust it and see what happens. Might have to
fiddle with it
over some time to get it right

== 2 of 4 ==
Date: Sun, Apr 24 2011 5:32 pm
From: "William Sommerwerck"

"KR" <kenreed1999@gmail.com> wrote in message
news:19295b80-cb87-416b-930b-05ae71bd9761@x37g2000prb.googlegroups.com...
On Apr 23, 5:36 am, "William Sommerwerck" <grizzledgee...@comcast.net>
wrote:

>>> The only reason I can guess for the poor timekeeping is that the
>>> circuitry/board running the clock is used on their 220 volt 50 Hz
>>> versions without modification, so the makers decided not to use
>>> line sync for the clock, and probably didn't want to spring for
>>> a crystal oscillator either, so used an RC one instead.

>> A chip would likely be designed to work at either frequency,
>> with a jumper making the selection.

> IF it is set to 50HZ and you are on a 60HZ supply -- then it
> would run faster, not slower.

That has nothing whatever to do with the point I was making.

> Open it up and see if there is some sort of trimmer capacitor
> near the clock chip, adjust it and see what happens. Might
> have to fiddle with it over some time to get it right.

I find it impossible to believe that /any/ microwave oven would use a
crystal or resonator -- which costs money -- when the power frequency is
/right there/, and free.

== 3 of 4 ==
Date: Sun, Apr 24 2011 8:45 pm
From: "Michael A. Terrell"

William Sommerwerck wrote:
>
> "KR" <kenreed1999@gmail.com> wrote in message
> news:19295b80-cb87-416b-930b-05ae71bd9761@x37g2000prb.googlegroups.com...
> On Apr 23, 5:36 am, "William Sommerwerck" <grizzledgee...@comcast.net>
> wrote:
>
> >>> The only reason I can guess for the poor timekeeping is that the
> >>> circuitry/board running the clock is used on their 220 volt 50 Hz
> >>> versions without modification, so the makers decided not to use
> >>> line sync for the clock, and probably didn't want to spring for
> >>> a crystal oscillator either, so used an RC one instead.
>
> >> A chip would likely be designed to work at either frequency,
> >> with a jumper making the selection.
>
> > IF it is set to 50HZ and you are on a 60HZ supply -- then it
> > would run faster, not slower.
>
> That has nothing whatever to do with the point I was making.
>
> > Open it up and see if there is some sort of trimmer capacitor
> > near the clock chip, adjust it and see what happens. Might
> > have to fiddle with it over some time to get it right.
>
> I find it impossible to believe that /any/ microwave oven would use a
> crystal or resonator -- which costs money -- when the power frequency is
> /right there/, and free.

They would use the same crystal as the microprocessor, and run the
clock in software.

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

== 4 of 4 ==
Date: Sun, Apr 24 2011 10:53 pm
From: John Tserkezis

Jeff Liebermann wrote:

>> Sorry, my email addy doesn't show it, but I'm in Australia. I've
>> verified that timing codes are NOT sent by ANY networks here.

> Are you talking about analog TV or digital TV? With analog, it was at
> the discretion of the station. With digital, it's inscribed into the
> ATSC (US) and DVB-T (everyone else) standards. Unfortunately, I don't
> know enough about either of these to explain how to get to these time
> codes.

I was talking about analogue. Digital here has only appeared in the
last decade or so, and even then, early on, there were no boxes you
could actually buy to do that. (funny though, the politicians could get
wide screen TVs and set top boxes donated quite easily to them - for
"testing purposes" you understand).

It's only the last few years the prices have come down to something
that's actually reasonable.

On the analogue side, we had *electronics* here that was compatible
with a variety of systems around the world for a LONG time, non of which
were compatible with our TV stations.

> In the US, the local PBS station (KTEH) went the other way. They
> claim to be sending time code signals, but none of my 3 assorted VCR
> boxes would find it.

At least you had TV stations that WERE transmitting codes, we didn't.
Not till digital anyway.

> on page 22 under "automatic time setting". The problem is that there
> has been no firmware update to deal with the 2007 change in daylight
> savings time.

Arrg. Don't start me on daylight savings. I'm actively unimpressed
unless the device supports USER DEFINABLE dst rules.

> My Tivo 2 can also use a PBS station for date and time, when connected
> to an antenna.

TiVo is another thing that failed miserably in Australia. The group in
charge of keeping things running in Australia and New Zealand is down to
7 people (from 100+?) and will only keep the current licence holders
going till that runs out.
Shame really. If it actually worked like it does in the US, it would
be quite viable. Except they knobbled a lot of the functionality, and
charged more for the privileged.

>> I suppose this comes down to the question of is mains locking "good
>> enough"?

> It's marginal. Loss of power means loss of clock, with no automatic
> method of restoring the real time. No thanks.

That's pretty much my attitude. Mains locking is cheaper to implement
than crystal locking, and if mains locking was better than crystal then
no-one would implement cyrstal locking in the first place.
But it IS better, AND you get very viable long term battery backed
timekeeping with crystals too. That leaves no reason for mains locked
clocks to be implemented at all, outside of "novelty" clocks. Really,
is saving two cents really worth it when you're pissing off your
customers that much?

>> Since I can't get a clear answer from anyone, I'm staying with crystals
>> or NTP where applicable.

> Perhaps a wind up clock would suffice?

I don't do windups. Outside of antiques that is.
But an antique isn't a timepiece, it's an example of a combination of
the limited technology of the day, doing a job that a two dollar Chinese
wrist-strapped device can today.
--
None of you exist, my Sysop types all this in.

==============================================================================
TOPIC: Problem with Atmel micro in a Kaon TV decoder
http://groups.google.com/group/sci.electronics.repair/t/d5fa629ff20dbe40?hl=en
==============================================================================

== 1 of 2 ==
Date: Sun, Apr 24 2011 6:20 pm
From: Jeroni Paul

On 24 abr, 04:01, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
> Hmmm. May have to sleep on this one.
>
> Does the processor's oscillator stay running while the device is in
> standby? The 89S52 does have a sleep mode where it turns the oscillator
> off but if it is responsible for waking up the rest of the device then
> I'd guess that it must stay running.
>
> If the oscillator stays running, given that the problem behavior also
> occurs when it goes to wake up the rest of the system from a state where
> it itself has already initialized, then it does sound like a firmware
> problem. Might be something like: wait for N timer ticks and if X has
> not happened then perform error recovery; but the actual time between N
> ticks can range from (N-1) to (N+1) if the waiting started just before
> or just after a tick event.
>
> --
> Rich Webb Norfolk, VA

The oscillator is running all the time. Don't know if it goes to some
idle mode but signals from the IR sensor and buttons change INT0 input
(pin 8 of TQFP package).

I tried to downgrade to an older firmware and the behavior is the
same. I think flashing another firmware only changes the firm for the
video decoder and not the code in the Atmel.

I thought maybe stopping the oscillator for a second or two while in
the wait loop will fix the problem. I tried to manually ground the
crystal output (I can see the dashes stop moving) and when it works it
doesn't reboot, but sometimes will go crazy probably due to poor or
intermittent contact I do with a wire to the crystal solder joint.

== 2 of 2 ==
Date: Sun, Apr 24 2011 7:32 pm
From: Rich Webb

On Sun, 24 Apr 2011 18:20:19 -0700 (PDT), Jeroni Paul
<JERONI.PAUL@terra.es> wrote:

>On 24 abr, 04:01, Rich Webb <bbew...@mapson.nozirev.ten> wrote:
>> Hmmm. May have to sleep on this one.
>>
>> Does the processor's oscillator stay running while the device is in
>> standby? The 89S52 does have a sleep mode where it turns the oscillator
>> off but if it is responsible for waking up the rest of the device then
>> I'd guess that it must stay running.
>>
>> If the oscillator stays running, given that the problem behavior also
>> occurs when it goes to wake up the rest of the system from a state where
>> it itself has already initialized, then it does sound like a firmware
>> problem. Might be something like: wait for N timer ticks and if X has
>> not happened then perform error recovery; but the actual time between N
>> ticks can range from (N-1) to (N+1) if the waiting started just before
>> or just after a tick event.
>>
>> --
>> Rich Webb Norfolk, VA
>
>The oscillator is running all the time. Don't know if it goes to some
>idle mode but signals from the IR sensor and buttons change INT0 input
>(pin 8 of TQFP package).
>
>I tried to downgrade to an older firmware and the behavior is the
>same. I think flashing another firmware only changes the firm for the
>video decoder and not the code in the Atmel.
>
>I thought maybe stopping the oscillator for a second or two while in
>the wait loop will fix the problem. I tried to manually ground the
>crystal output (I can see the dashes stop moving) and when it works it
>doesn't reboot, but sometimes will go crazy probably due to poor or
>intermittent contact I do with a wire to the crystal solder joint.

Something like that might be an option. If you could identify a pin that
changes state when it begins the operate sequence that's giving you
trouble, use that event to slow down the clock just long enough to get
past the difficult spot.

Something like (block diagram; use fixed-pitch)

.-------.
| |
| |
|12 MHz o-----o-------------------.
| | | |
'-------' ? |
| |
.-----o----. .------o------.
| | | |
.----o one-shot o-------o divide by 2 o------.
| | | | | |
| '----------' '-------------' |
| |
.-o--------------------------------------------o---------.
| the pin X1 |
| |
| 89S52 |
| |
'--------------------------------------------------------'
(created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

Where the event on "the pin" fires the one-shot (could be a counter
that's run from the 12 MHz clock or maybe the old standby, a 555). That
enables the divide by 2 so you briefly run at 6 MHz, slowing everything
down.

Of course, an external clock and a crystal oscillator won't play well
together. But this would probably want a small daughter board, anyway,
and you could disconnect the crystal altogether and run with a canned 12
MHz oscillator.

It wants a clocked flip-flop somewhere there so that it changes speed
cleanly.

--
Rich Webb Norfolk, VA

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

== 1 of 2 ==
Date: Sun, Apr 24 2011 6:25 pm
From: who where

On Sat, 23 Apr 2011 16:24:17 +0100, "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 was always my understanding that the "oversized" PTH was a
deliberate choice. If significant current needs to pass to both
planes, a (proper, of course, not RoHS) solder plug enhances the
through-plating's capability.

== 2 of 2 ==
Date: Sun, Apr 24 2011 8:48 pm
From: "Michael A. Terrell"

who where wrote:
>
> On Sat, 23 Apr 2011 16:24:17 +0100, "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 was always my understanding that the "oversized" PTH was a
> deliberate choice. If significant current needs to pass to both
> planes, a (proper, of course, not RoHS) solder plug enhances the
> through-plating's capability.

It makes more sense to just specify a thicker plating on the PTH.
Solder his a higher resistance, and is much weaker.

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

==============================================================================
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 2 ==
Date: Sun, Apr 24 2011 6:32 pm
From: who where

On Sun, 24 Apr 2011 22:03:16 +0100, "Stephen" <i.want.spam@spam.com>
wrote:

>OK, I'll get some 22uF 50V 105 degree C ones ordered in then Do they have to
>be low ESR? if so I'' go for the Panasonic FM series that I used to replace
>the secondary output electrolytics.
>
>If a capacitor has gone dry, wouldn't there be a clue like bulging tops,
>leaking brown crud, and a horrible smell when they get hot?

Those symptoms occur some time *after* the cap's performance degrades
to the point of compromising the PSU.

Agree with the others, the small cap on the UC3842 is the most likely
candidate. Note that it *may* be a surface mount type and not an
aluminium electrolytic.

== 2 of 2 ==
Date: Mon, Apr 25 2011 12:50 am
From: Kripton

On 2011-04-24 23:03:16 +0200, "Stephen" <i.want.spam@spam.com> said:

> If a capacitor has gone dry, wouldn't there be a clue like bulging tops,
> leaking brown crud, and a horrible smell when they get hot?
>
> Regards,
>
> Stephen

you can make a quick esr analog meter to check all your caps
the small capacitor next to the uc3842 aways fails to an esr meter
even a cheap build from scratch analog one.

my web site contains easy and more complex esr meter to build yourself
regards,

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

--
---
Kripton

==============================================================================
TOPIC: HAKKO SOLDERING STATION WANTED
http://groups.google.com/group/sci.electronics.repair/t/0981538b62f81654?hl=en
==============================================================================

== 1 of 1 ==
Date: Sun, Apr 24 2011 6:42 pm
From: justme

Or, similar. Gotta be cheap.

Thanks

==============================================================================
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 3 ==
Date: Sun, Apr 24 2011 7:17 pm
From: Jeff Liebermann

On Sun, 24 Apr 2011 21:29:01 +0100, "N_Cook" <diverse@tcp.co.uk>
wrote:

>Did you try silipads in your comparison study ? where they around in 93 ?

Memory fault and I goofed. It was about 1983. I thought I had
scanned and posted the manual for the Intech M3600 radio, but I guess
not.

<http://www.bergquistcompany.com/thermal_materials/sil-pad.htm>
Yes. They were a total disaster. Berquest and Thermalloy were making
them in one thickness and material type at the time. I don't recall
what it was, but might be able to find the data in my "archives". What
Sil-pads were good for was the ease of handling, consistency, and
cleanliness. I would have used them if they were suitable. Well, I
did use them for TO-3 and other non-RF power devices. However, this
was a performance problem, not a manufacturing exercise. The price
you pay for the benefits of silpads is a modest thermal resistance,
which was unacceptable.

We were trying to squeeze as much power out of a pair of transistors,
that would normally dissipate about 175 watts each. This had to pass
through a 30 mm^2 base to a much larger heat sink. Almost any thermal
resistance between the xsistor base and heat sink would raise the
xsistor temperature enough to initiate a thermal shutdown. Under
ideal circumstances, the heat sink should be very close to the
temperature of the transistor base. It was, but when a few degrees of
differential temperature translates into many watts LESS of RF output,
any difference was considered a bad thing. The transistors could
produce almost any RF power output desired, if only they could be kept
sufficiently cool. The other incentive was above a certain junction
temperature (which I've forgotten), thermal runaway is a real problem.

There was another problem with silpads. The base of the xistor was a
round disk with ears. We had several bases, but this was the problem
maker:
<http://www.qsl.net/df7tv/datasheets/sd1487.pdf>
When we torqued down on the mounting screws, the sil-pad material
tended to bunch together near the mounting holes, resulting in the
base taking the shape of a "bow" with less pressure in the middle. Of
course, the place where we needed the most compression was in the
middle. I contrived a layered spacer that sorta worked, but it
increased the thermal resistance even more by increasing the gap.

Incidentally, I also tried beryllium oxide insulators, mica
insulators, aluminum foil, brass shims, and various home made mixes of
aluminum oxide dust. All of them worked when properly applied and
with proper compression. However, direct metal to metal polished
contact worked best.

--
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

== 2 of 3 ==
Date: Sun, Apr 24 2011 7:28 pm
From: Jeff Liebermann

On Sun, 24 Apr 2011 19:27:39 +0000 (UTC), Meat Plow
<mhywattt@yahoo.com> wrote:

>The best compound is one of micronized silver and ceramic particles.
>After all you are trying to fill microscopic voids between device and
>heatsink so they need to fit.

If you must use a compound, I suggest a mix of some kind of grease
that will vaporize when the heat is applied (hopefully leaving little
residue), and diamond dust:
<http://en.wikipedia.org/wiki/Material_properties_of_diamond#Thermal_conductivity>
Silver is good, but diamonds are much better.

However, the ultimate in thermal conductivity is still metal to metal.
A good example are the diodes used in automotive alternators and
industrial power equipment. These diodes are press fitted with an
arbor press into the heat sink. Metal to metal at it best with not
even microscopic gaps. I tried to get the RF power xsistor vendors
interested in an interferenc fit package, but because I didn't have a
sufficiently large purchase order, they weren't interested.

--
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

== 3 of 3 ==
Date: Sun, Apr 24 2011 8:07 pm
From: "Barry"

"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_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

This stuff is NOT a silicone grease but rather a room temperature
vulcanizing silicone rubber. There is no copper in it, and it is a poor
heat conductor. General Electric used to be the manufacturer, but it
appears that they have sold out to a Chinese company. If memory serves
it used to be either RTV-60, RTV-650, or RTV-106. I cannot remember
which is the two-part and which is the one-part material. MG Chemicals
is a distributor for Momentive Performance Materials, the _obviously_
Chinese company that makes it now. They do make two higher thermal
conductivity silicones known as TSE3331 and TSE3941. The former is a
grey potting and encapsulating compound while the latter is a white
adhesive.

As Jeff Liebermann <jeffl@cruzio.com> pointed out, the smoother the
surfaces are and the closer they fit, the better the heat transfer will
be. All the silicone heat transfer grease does is fill the microscopic
void spaces (dead air space is a good thermal insulator).

Working around chemists, I had easy access to silicone vacuum stopcock
grease. I have used it in a pinch for thermal grease and it worked well.
You can find a similar grease in the plumbing department of Lowes and
Home Depot. It is used to lubricate valve stems, rubber seals, and those
ungodly expensive ceramic Price-Pfister faucets. It will work far better
than any Permatex product as a heat transfer grease.

Oh, and one other reason to not use Permatex in this application. This
silicone is an acetoxy cure which means it releases corrosive acetic acid
when it cures.

Dr. Barry L. Ornitz WA4VZQ ham_call_letters at live.com

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