Bob,
The vendor has said that they did not want the unit back. So...
I opened it up. Crudely, I admit. I learned a few things. I was concerned
about the outer case heating up too much when I was trying to remove the
solder. Turns out that the outer case doesn't touch anything except the pins,
so it can get pretty hot without any damage. Unfortunately, I used a bit of
brute force to remove the casing after scraping away as much of the solder as
I could and after cracking the solder seal with a hammer and screw driver.
Even using more heat, I'm not sure of the best way to remove the case. Neither
solder wick nor a vacuum desoldering tool is likely to remove all of the
solder between the top case and the bottom.
Even so, I got the case off. Somewhat bent, even bent the bottom circuit board
a bit. I discovered that there is a 2mm hole in the top that allows a variable
resistor to be adjusted. You need a pretty long, small screwdriver / adjusting
tool to do that, but that is probably for setting the center point. I would
try to remove the solder rather than drilling, or drill upside down to prevent
solder flakes from falling inside.
Also, I found that the -D on my part number appears to correspond to the board
revision, which is marked "Rev D". So the -C and -D parts probably have the
same specifications. And, on the inside there is a marking "92.0" which I
believe would be the set point for this specific crystal. So if I took the
crystal out, I would know where to design the set point for a custom unit
(currently beyond my skills, but who knows...).
From there, I removed the bottom casing. That caused additional damage, some
lifted traces and even one very small part (tiny, SMD, who knows?).
But, I then soldered wires directly to the board, making patches for the
lifted traces.
I plugged it in.
I turned it on.
Success!
I gave it 12v which should supply 2A, but it dropped the voltage down to just
over 9V. Even so, I got a nice sine wave out at around 4.999790Mhz according
to my (uncalibrated) scope and around 800mV (into 50 ohm, DC). That was with
nothing attached to the adjustment pin. After some time, the frequency
stabilized at 5.000014Mhz and the voltage came back up to 10v. When I attached
the adjustment pin to ground, there was no change. When I attached the
adjustment pin to Vref (which is at 6.15v), the frequency dropped to
5.000010Mhz. So apparently, these units adjust negatively. But also have a
very wide adjustment range of 4Hz (8e-7). I am assuming that the adjustment
range is 0..6v. I attached the adjustment pin to +10v and the frequency
dropped another 3Hz for a 1.4e-6 adjustment range.
I don't expect that this specific unit will be very useful given the damage
that I caused opening it up. But, probably there were just bad connections
internally, so if I were much more careful in the disassembly, I could
probably have fixed it. Something to keep in mind for the next unit.
I may be wrong for what the variable resistor does. Turning it made no
difference in the frequency.
I also suspect, but don't know that the difference from 5Mhz is due to the
frequency counter being uncalibrated. It could also because I damaged the unit
or just because it is very far off from where it should be.
Still, I learned a lot, and well worth the time spent.
Mike
Hi
The one advantage you have in testing a used OCXO is you have a pretty good
idea of how
you are going to use it. If phase noise does not matter to you … no need to
test. I’d always check
that it tunes on freq with reasonable EFC range left over. I’d also make sure
that it warms up
properly (oven works) and that it has a reasonable output. What goes on the
list past that …
it depends on what you need.
The gear you have will check aging and get it set on frequency fine. It will
check it for “wander”
as your lab heats up and cools down. With a GPSDO and a simple phase lock, a
DVM may be
all you really need to do most of that. You will not have a proper ADEV, but
you will know it works
pretty well (or not ..).
A lightbulb oven / bench / fridge /freezer proces can give you a wide range TC
if you need it.
If you do get into phase noise, a sound card system will get you going. For
ADEV, the 10811’s
tune far enough that a single mixer system with your 53131 will give you good
data. Both
of those will involve some building, but not a lot of money.
There is one thing about the 10811’s: They are not sealed units. They tend to
soak up humidity
when stored in most parts of the country. You may want to run them for a month
or three
before doing any fancy testing.
Bob
On Feb 18, 2016, at 7:40 AM, Adrian Godwin <[email protected]> wrote:
I have a small collection of 10811 and similar oscillators here, collected
from hamfests rather than china (and mostly pre-ebay).
What sort of testing regime would you put them through ? I don't have
anything as exotic as a timepod but I do have an HP53131A, the Tait Rb
source, and a KS-24361 set up. And always keen to get hints on the
acquisition of new toys !
On Thu, Feb 18, 2016 at 12:09 PM, Bob Camp <[email protected]> wrote:
Hi
It is *much* better to have an OCXO that you do not need to test to death.
There is simply to much testing to do. A modern factory does not test the
quality into the product (of any sort) they design in and build it in. The
same
is true of the normal customer for virtually any component. They make sure
the parts come from somebody they can trust and save a lot of testing time.
That said, yes, I have a pile of scrap parts sitting in front of me as I
type this.
It’s a hobby. Time does not count. It lets me play with all sorts of toys
doing
the testing. I occasionally learn things in the process. Mostly I learn
that
my hope of a 100% perfect batch is still a dream ….
Bob
On Feb 17, 2016, at 9:56 PM, [email protected] wrote:
Bob,
In this case, I know how it was taken off the board - it wasn't. They
just cut
the board around it. I had to remove it myself. Nice thing about that,
is that
I got a nice plastic, pre-formed part that fits between the board and the
OCXO, probably as an insulator.
You are also right about the number of things that you need to test to
make
sure that one of these is fully functional. However, this is a "starter"
OCXO
for me and I don't yet have the equipment to perform the tests. The best
that
I can do is to make sure that, when powered up
1. I see something that sort of looks like a sine wave at a reasonable
magnitude.
2. My 2465B CT frequency counter thinks that it is somewhere near 5Mhz.
3. If I apply gnd, or VRef to the adjustment pin I see the frequency
change
at least a small amount.
Without more equipment, there isn't much more that I can do to test.
Unless
you have some suggestions?
Mike
Hi
Best guess is these things get taken off the board with either a big
torch or a charcoal fire.
You can ask Mr Google to dig up pictures of the process. Depending on
just how quick
they are, the insides of the OCXO can easily be reflowed. The
likelihood of it reflowing and
cooling back to a reliable joint … not real good.
Bob
On Feb 17, 2016, at 5:16 AM, Andrea Baldoni <[email protected]>
wrote:
On Tue, Feb 16, 2016 at 07:58:21PM -0500, [email protected] wrote:
I just received a 5Mhz OCXO from eBay (MTI 260-0624-D OCXO). After
testing it,
it is clear that it is defective.
1. It never heats up.
2. The reference voltage is zero.
3. Only noise is seen on the output pin.
I had the same issue with some of them. It's very likely that the
internal
solder connections from pins to PCB are broken, at least, the one for
power.
It happens because the inner oven is heavy and there isn't any thermal
insulator (besides air) to keep it from moving.
Wheter the crystal has been damaged or not, it's unknown. I had one
where the
crystal actually fell off from its supports too.
I posted a link to photos of the internals, time ago. The link is dead
now
and I don't think to have the photos anymore but perhaps someone
downloaded
them.
Best regards,
Andrea Baldoni
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Best regards,
Timenut mailto:[email protected]
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