Okay, I pulled the black box cover off and was greeted by a picture of how
things should be made. After some considerable time staring at the veritable
work of art, I thought I saw the crystal hiding behind the foam. So I gently
removed the foam and marked on the xtal is 79 degrees C. Cool, Well actually
that's hot! So I have powered it up for 30 minutes and measured the
temperature with a very accurate temperature gun I use for measuring preheating
on rework jobs. Huh, its sitting dead on 60 degree's. I think therein, lies
our problem, the crystal never reaches turning point. According to the fine
manual, Increasing R8 lowers the temperature. Therefore, If I decrease R8 It
should theoretically, increase the temperature?
The conundrum is, Shall I just change R8 value or perhaps there is something
else wrong.
What do you think Guys, R8 or something else?
I am not going further without some of the abundant collective wisdom and
experience contained in the time-nuts members!
-marki
-----Original Message-----
From: Mark C. Stephens
Sent: Friday, 24 May 2013 2:01 AM
To: Discussion of precise time and frequency measurement
Subject: RE: [time-nuts] 9390 GPS RX
Ed,
Okay, Lying there I couldn't stop thinking about its lone Ball.
So I setup the jig, Powered it up and yep, after half an hour the frequency is
doing the up/down swing thing. Interesting, I just happened to come across
that page that reckons you can rejuvenate a lamp with a heat gun. So I
thought, hmm that's easy, let's try that, so I did, and the frequency is not
swinging so quickly now. Could be an symptom, but I think coincidence.
Anyway, next I connected a DVM to the xtal volts output monitor pin as per the
manual.
Uhuh, its swinging in tandem with the frequency swing of the 10 Mhz output
swing.
Gets to 2V and then swings down to -2V
Nowhere near the 8V defined in the manual.
So I tried adjusting the trimmer as per the manual.
Nope won't go above 2V at the fully clockwise limit of the trimmer.
So that is where I am at. Looks like I will have to pull it apart and fix it
then.
Does it sound/look like the crystal has gone out of adjustable range?
-marki
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Mark C. Stephens
Sent: Friday, 24 May 2013 12:22 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 9390 GPS RX
Hey Ed, Well I have its Ball (just one? ;) Efratom out on the bench.
Seems they built this stuff to service, huh? Nice.
I managed to make a mating connector out of 2.54mm pitch header strip as per
your suggestion.
Whew, that was my biggest concern!
Anyway, its after midnight and I have a full day ahead, Looking forward to
getting this old gal working again.
I can't help giving the 9390 a reassuring pat every time I walk past it ;) its
sitting there merrily running off the house standard although PDOP hasn't gone
below 4 which has me a tad worried.
It seems, I have become quite attached to this 9390 :p
-marki
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf
Of Ed Palmer
Sent: Thursday, 23 May 2013 1:16 AM
To: [email protected]
Subject: Re: [time-nuts] 9390 GPS RX
On 5/22/2013 4:58 AM, Mark C. Stephens wrote:
It's a 9390-55024
I have plugged my counter into the Efratom rubidium oscillator thing and
disconnected the EFC.
It is actually wobbling ~ +/-650Hz, peaking as much as +/- 1KHz.
So, hazarding a guess, something is very wrong inside the black box thing.
Is it really wobbling around randomly, or is it sweeping up and down.
Your counter could be fooling you by taking 'snapshots' at intervals dependent
on the gate time setting. If the frequency is wobbling randomly that would
likely mean an actual fault in the FRK rather than something that needs
adjusting. If it's sweeping up and down, that means that it's searching for
the rubidium signal, but not finding it.
Every rubidium will do that, but it should find the signal within 5 - 10
minutes. That could mean an adjustment or a fault depending on the actual
frequency range that it's sweeping over. Obviously, you want the frequency
range to be 10 MHz +- something.
My biggest fear is, wherever will I get the 'Winchester' connector used on this
oscillator?
That's easy. Improvise! Go into your box of junk connectors and find a female
connector that uses pins of approximately the same diameter.
Remove the sockets from the connector body, solder wires onto them, insulate
them with tape or heat shrink and slide them over the pins on the FRK
connector. For example, RS-232 sockets are a bit big, but could be squashed
down. Floppy disk connectors are usually really easy to remove from the body.
I'm not sure if they'd work, but you get the idea. It doesn't have to be neat
or elegant. It's just temporary for a test.
Ed
What I mean is, for a proper bench job, according to the manual, I'd have to
remove the whole rubidium from the 9390 and put it on the clean bench for
disassembly.
Then I can connect various voltmeters to monitor the various signals, and if
needed, replace parts and re-align.
However, I am unwilling to lop off the connector in the 9390, to only have to
put it back on/in after Mr. Balls Efratom is back to normal.
The other way, I suppose is to bodge up wires from the inside of the connector
to some sort of temporary Jig for the service job.
Reading the Most Interesting FRK.PDF, it sounds like the crystal oscillator
assembly has issues, whether the crystal oven is broken or similar.
That is a really interesting document, worth the read, even just for
the heck of it ;)
-marki
