32.768 KHz crystal failure

N

N_Cook

Guest
One of those tiny barrel watch-size ones. Measured 13 ohms across the pins
before and after desoldering. Could not resist grinding the end off to have
a butchers'. Heat from grinding destroyed whatever ohmic path there was.
I've never looked inside one before. Tuning fork type form with 4 complex
tapering tracks, silver looking, on each face, under a x30 microscope.
Presumably silver migration/silver mica cap disease, only a few atoms
bridging a 100 micron gap between tracks to cause failure.
Previously I've come across ceramic resonator and filter failure due to
ohmic , presumed Ag migration .
The closure end with the wires, is the barrel swaged over a tiny paxolin
disc exactly like can type electrolytic capacitor.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
 
On Mon, 29 Jun 2009 16:26:37 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

One of those tiny barrel watch-size ones. Measured 13 ohms across the pins
before and after desoldering. Could not resist grinding the end off to have
a butchers'. Heat from grinding destroyed whatever ohmic path there was.
I've never looked inside one before. Tuning fork type form with 4 complex
tapering tracks, silver looking, on each face, under a x30 microscope.
Presumably silver migration/silver mica cap disease, only a few atoms
bridging a 100 micron gap between tracks to cause failure.
Previously I've come across ceramic resonator and filter failure due to
ohmic , presumed Ag migration .
The closure end with the wires, is the barrel swaged over a tiny paxolin
disc exactly like can type electrolytic capacitor.
Click to expand...
I've never observed that type of failure. I've seen crystals that
resonate at an overtone rather than their rated frequency. Others were
shattered by physical impact (you can hear the shards rattling
inside), and others just wouldn't start oscillating without some
coaxing, either by heating or freezing. I've also shattered a crystal
when I cut up a circuit board with a band saw.

The strangest failure was in an IBM PC whose graphics chip was
outputting H & V sync frequencies that were much higher than normal,
but were not an integer multiple of the correct frequency. I traced
the fault to a crystal oscillator. It was suggested to me that maybe a
quartz dag that was present during manufacturing had later fallen off.
This would reduce the mass of the crystal, resulting in an increase in
its resonant frequency.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
 
Franc Zabkar <fzabkar@iinternode.on.net> wrote in message
news:a37i45lv4f5b1d4kmjn37csr2m9ihbktts@4ax.com...
On Mon, 29 Jun 2009 16:26:37 +0100, "N_Cook" <diverse@tcp.co.uk> put
finger to keyboard and composed:

One of those tiny barrel watch-size ones. Measured 13 ohms across the
pins
before and after desoldering. Could not resist grinding the end off to
have
a butchers'. Heat from grinding destroyed whatever ohmic path there was.
I've never looked inside one before. Tuning fork type form with 4 complex
tapering tracks, silver looking, on each face, under a x30 microscope.
Presumably silver migration/silver mica cap disease, only a few atoms
bridging a 100 micron gap between tracks to cause failure.
Previously I've come across ceramic resonator and filter failure due to
ohmic , presumed Ag migration .
The closure end with the wires, is the barrel swaged over a tiny paxolin
disc exactly like can type electrolytic capacitor.

I've never observed that type of failure. I've seen crystals that
resonate at an overtone rather than their rated frequency. Others were
shattered by physical impact (you can hear the shards rattling
inside), and others just wouldn't start oscillating without some
coaxing, either by heating or freezing. I've also shattered a crystal
when I cut up a circuit board with a band saw.

The strangest failure was in an IBM PC whose graphics chip was
outputting H & V sync frequencies that were much higher than normal,
but were not an integer multiple of the correct frequency. I traced
the fault to a crystal oscillator. It was suggested to me that maybe a
quartz dag that was present during manufacturing had later fallen off.
This would reduce the mass of the crystal, resulting in an increase in
its resonant frequency.

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.
Click to expand...
Certainly not the simple slab with simple silvering on each side. As the
open ends of the tuning fork look ground, on a 30x ,then perhaps literally a
tuning fork , actively tuned to frequency, and the odd trace patterning is
for modulation of capacitance. I don't suppose a 13 ohm build up of Ag over
100 micron gap would be observable, as stable at 13R via soldering/movement
doubtful it was some mechanical breakage/movement.


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
 
N_Cook <diverse@tcp.co.uk> wrote in message
news:h2amhb$kut$1@news.motzarella.org...
One of those tiny barrel watch-size ones. Measured 13 ohms across the pins
before and after desoldering. Could not resist grinding the end off to
have
a butchers'. Heat from grinding destroyed whatever ohmic path there was.
I've never looked inside one before. Tuning fork type form with 4 complex
tapering tracks, silver looking, on each face, under a x30 microscope.
Presumably silver migration/silver mica cap disease, only a few atoms
bridging a 100 micron gap between tracks to cause failure.
Previously I've come across ceramic resonator and filter failure due to
ohmic , presumed Ag migration .
The closure end with the wires, is the barrel swaged over a tiny paxolin
disc exactly like can type electrolytic capacitor.
Click to expand...

My 30x microscope+camera can only capture about 1mm diameter
http://home.graffiti.net/diverse:graffiti.net/quartz.jpg
overal quartz sliver is 6.5x1.5x0.3mm
White is the silvering with some illumination flare, some connected to one
pin and some connected to the other pin, similar but not the same on the
other side. G is the area of quartz ground down end and face, a bit ,
compared to the lower finger of the "tuning fork".
Area near the notch , dimension between + and + is 0.75mm , half the width.
So minimum gap between silverings about 60 micron.
Width of notch about 0.25mm
There is also silvering along some of the 0.3mm edges, so very complicated
silvering geometries


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/
 
On Mon, 29 Jun 2009 16:26:37 +0100, "N_Cook" <diverse@tcp.co.uk>wrote:

One of those tiny barrel watch-size ones. Measured 13 ohms across the pins
before and after desoldering. Could not resist grinding the end off to have
a butchers'. Heat from grinding destroyed whatever ohmic path there was.
I've never looked inside one before. Tuning fork type form with 4 complex
tapering tracks, silver looking, on each face, under a x30 microscope.
Presumably silver migration/silver mica cap disease, only a few atoms
bridging a 100 micron gap between tracks to cause failure.
Previously I've come across ceramic resonator and filter failure due to
ohmic , presumed Ag migration .
The closure end with the wires, is the barrel swaged over a tiny paxolin
disc exactly like can type electrolytic capacitor.
Click to expand...
It is a tuning fork reference. Bulova type, transistor switched to
oscillate at 360 hz.
 
It is a tuning fork reference. Bulova type, transistor switched to
oscillate at 360 hz.
Click to expand...
Non-sequitur. The Bulova Accutron, dating back more than 45 years, used a
rather large tuning fork. I still have my father's.
 
On Tue, 30 Jun 2009 08:25:19 -0700, "William Sommerwerck"
<grizzledgeezer@comcast.net>wrote:

It is a tuning fork reference. Bulova type, transistor switched to
oscillate at 360 hz.

Non-sequitur. The Bulova Accutron, dating back more than 45 years, used a
rather large tuning fork. I still have my father's.
Click to expand...
I have one made in 1965, solid gold.
 
On Tue, 30 Jun 2009 15:09:10 +0100, "N_Cook" <diverse@tcp.co.uk>wrote:

N_Cook <diverse@tcp.co.uk> wrote in message
news:h2amhb$kut$1@news.motzarella.org...
One of those tiny barrel watch-size ones. Measured 13 ohms across the pins
before and after desoldering. Could not resist grinding the end off to
have
a butchers'. Heat from grinding destroyed whatever ohmic path there was.
I've never looked inside one before. Tuning fork type form with 4 complex
tapering tracks, silver looking, on each face, under a x30 microscope.
Presumably silver migration/silver mica cap disease, only a few atoms
bridging a 100 micron gap between tracks to cause failure.
Previously I've come across ceramic resonator and filter failure due to
ohmic , presumed Ag migration .
The closure end with the wires, is the barrel swaged over a tiny paxolin
disc exactly like can type electrolytic capacitor.





My 30x microscope+camera can only capture about 1mm diameter
http://home.graffiti.net/diverse:graffiti.net/quartz.jpg
overal quartz sliver is 6.5x1.5x0.3mm
White is the silvering with some illumination flare, some connected to one
pin and some connected to the other pin, similar but not the same on the
other side. G is the area of quartz ground down end and face, a bit ,
compared to the lower finger of the "tuning fork".
Area near the notch , dimension between + and + is 0.75mm , half the width.
So minimum gap between silverings about 60 micron.
Width of notch about 0.25mm
There is also silvering along some of the 0.3mm edges, so very complicated
silvering geometries
Click to expand...
So it's not a tuning fork but rather a crystal.
 
Meat Plow wrote:
So it's not a tuning fork but rather a crystal.
Click to expand...

That cut is referred to as a 'Tuning fork crystal', because of the
long, thin shape.

<http://www.google.com/search?q=tuning+fork+watch+crystal&rls=com.microsoft:en-us&ie=UTF-8&oe=UTF-8&startIndex=&startPage=1>

A 32768 hz crystal is used by some MPU ICs with a built in PLL
multiplier. The MC68340, of the MC68020 family is one example.

Improper loading can cause it to run at the wrong frequency, and a
10:1 scope probe will detune it. I had to use a special Tektronics FET
input scope probe to troubleshoot a design problem on a custom embedded
controller.

These crystals are fragile, and need to be mounted so that they can't
vibrate. Most, if not all datasheets recommend laying them flat to the
PC board and soldering the top end of the cap to a pad on the PC board,
but a lot of designers fail to do this.


--
You can't have a sense of humor, if you have no sense!
 
On Wed, 01 Jul 2009 10:31:01 -0400, "Michael A. Terrell"
<mike.terrell@earthlink.net>wrote:

Meat Plow wrote:

So it's not a tuning fork but rather a crystal.


That cut is referred to as a 'Tuning fork crystal', because of the
long, thin shape.

http://www.google.com/search?q=tuning+fork+watch+crystal&rls=com.microsoft:en-us&ie=UTF-8&oe=UTF-8&startIndex=&startPage=1

A 32768 hz crystal is used by some MPU ICs with a built in PLL
multiplier. The MC68340, of the MC68020 family is one example.

Improper loading can cause it to run at the wrong frequency, and a
10:1 scope probe will detune it. I had to use a special Tektronics FET
input scope probe to troubleshoot a design problem on a custom embedded
controller.

These crystals are fragile, and need to be mounted so that they can't
vibrate. Most, if not all datasheets recommend laying them flat to the
PC board and soldering the top end of the cap to a pad on the PC board,
but a lot of designers fail to do this.
Click to expand...
Very familiar with xtal controlled phase locked loop circuits for
decades, just never heard that description.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top