Hi Garren,
Yes, you're right. Silly me, I made the mistake of believing what was
written in the manual which says 2-12 volts. When I measure it, I see
~2-16 volts. Let that be a warning to you. This isn't the first time
that manual has led me astray! I should have known better.
Did you notice that the voltage changes as you adjust the capacitor on
the side? If the adjustment is at it's limit, you may have to change
capacitors A3C11 and maybe A3C12 to get the oscillator back on
frequency. It's explained in the manual. :-) Let it settle for at
least a few days and see which direction the crystal control voltage
moves. If it falls you're fine. If it rises higher, you may want to
look at the capacitors. If you have to change the capacitors, be sure
to use NP0/C0G type capacitors.
Bob's comments regarding the C-field are right on the money. It's for
fine tuning after you have a stable lock. It won't help you obtain or
maintain a lock. You won't be able to adjust it without a known, stable
10 MHz reference source like the Tbolt and some good measurement equipment.
Ed
On 2/10/2013 9:27 AM, Garren Davis wrote:
Hi Ed,
The voltage swings from 2v to 17v. Doesn't that mean I have about 4 to 5 volt
margin if it's locked at 12 volts?
I had to adjust the capacitor out almost all the way to get it to lock. If I
need to adjust it more can I use the C-field adjustment or should I stay away
from that?
Garren
On Feb 9, 2013, at 10:48 PM, "Ed Palmer" <[email protected]> wrote:
Hi Garren,
Congrats on your repair. Since the crystal control voltage is spec'd as ~1 to
12 Vdc, you're apparently holding onto lock by the narrowest of margins. You
definitely want to adjust the oscillator to bring that voltage closer to the
middle of it's range.
Ed
On 2/9/2013 11:38 AM, Garren Davis wrote:
Found my problem with the FRK. R31 on the Osc board was burned and open. This
was caused by a shorted C16. Replaced and it is now locked. The lock voltage is
12.7v. Is this good or should it be lower?
Garren
On Feb 9, 2013, at 6:10 AM, "Bob Camp" <[email protected]> wrote:
Hi
How old is the FRK? Does it look like it's been run without a heat sink for
very long? They tend to get flaky if run for a while (many months) without heat
sinking. There's nothing mysterious about it. The MTBF of the parts gets
noticeably worse as the unit heats up.
Bob
On Feb 9, 2013, at 1:09 AM, Garren Davis <[email protected]> wrote:
Well for some reason the 10 Mhz stopped working on the FRK. Don't know why.
Started up the thunderbolt. It acquired satellites but then the DAC voltage
went to -5 volts. It's been there for an hour. Will this change after the unit
stabilizes? Going to bed. Will check it tomorrow.
Garren
On Feb 8, 2013, at 8:25 PM, "Ed Palmer" <[email protected]> wrote:
Hi Garren,
I suggest that you get the Thunderbolt working first. Without a known 10 MHz
source to compare to, you're flying blind. Once the Tbolt is running, you
should be able to check the frequency of the FRK by feeding both into your
scope. Trigger on the Tbolt and watch what the FRK does. You should see the
trace scrolling in one direction, then slow down, then stop, then scroll the
other direction. The 'stop' point is at 10 MHz. The frequency sweeps a total
of 20-30 Hz so it's easy to see. If you don't see the 'stop' point, the FRK
isn't getting to 10 MHz. Now use the best frequency counter you've got to
measure the Tbolt. Regardless of the calibration of your counter, the number
your counter gives you becomes your 'new' 10 MHz. Now measure the FRK to see
if it's running fast or slow.
You should check the temperature of the lamp. It's easy to get at by removing
the cover in the center of the heat sink. Probably best to remove the cover
and then power down before you go poking around inside! The temperature of the
cavity is also important, but getting to it is more of a hassle - don't go
there if you don't have to.
Of course, check for the normal things like internal power supply voltages,
ripple, current drain (both initial and steady-state), etc.
Regarding your second message, yes, the adjustment under the heat sink near the
edge is the C-field. That won't help you at this point. The adjustment in the
center of one side is the VCO. You could try adjusting it, but like I said,
you're flying blind at this point. You won't know if you're adjusting closer
to 10 MHz or further away.
Good luck,
Ed
On 2/8/2013 6:12 PM, Garren Davis wrote:
Been lurking on the list for a while and finally started playing with a FRK-L
rubidium frequency standard. I've had this thing for a while and decided to
power it up and see what it would do. I do not get a lock. What I see is the
lamp voltage at 8.54 volts which I think is good but the xtal control voltage
swings from 2 volts to 15 volts and back to 2 volts and keeps cycling like
that. I don't have a good frequency counter but I have a 3 Ghz 40 G/sample
scope and it shows that the 10 MHz signal is there. I just don't know how
accurate it is. Has anyone seen a problem like this? Can anyone point me to a
place to start debugging this? I have the schematics and test tools. I am a
test engineer so I'm not afraid to poke around in the guts of this thing.
Hopefully I can get this thing running. I also have a thunderbolt that I'll get
running this weekend. I don't know how deep I'll get into this time-nuts thing
but I have this nice scope and a Wavecrest sitting in my garage and I
'd like to put them to use. Any help would be appreciated.
Garren
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