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32.768 KHz crystal failure

N

N_Cook

Jan 1, 1970
0
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.
 
F

Franc Zabkar

Jan 1, 1970
0
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
 
N

N_Cook

Jan 1, 1970
0
Franc Zabkar said:
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

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.
 
N

N_Cook

Jan 1, 1970
0
N_Cook said:
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
 
W

William Sommerwerck

Jan 1, 1970
0
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.
 
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