[time-nuts] FE 5680A Warning
Pete Lancashire
pete at petelancashire.com
Sun Nov 13 18:30:12 UTC 2011
Telcom upgrade, just like where all the Thuderbolts came from
On Sun, Nov 13, 2011 at 9:21 AM, Chuck Forsberg WA7KGX N2469R
<caf at omen.com> wrote:
> Seems like a lot of folks selling these lately.
> Curious minds would like to know why.
>
> On 11/13/2011 07:15 AM, EWKehren at aol.com wrote:
>>
>> Pete
>> That is exactly the same math I did, there is no other choice but it would
>> be nice if some one can help on the C field. I just finished mounting it
>> on
>> a heat sink added a Toshiba 15 V 3 A power supply and a 7805 and will run
>> it for a month with out changing any thing. Will read it twice a day and
>> see how it behaves.
>> Bert
>>
>>
>> In a message dated 11/13/2011 9:24:47 A.M. Eastern Standard Time,
>> bell.peter at gmail.com writes:
>>
>> Yes, I'm quite sure this is how it works - if you scope the snap diode
>> drive you can quite clearly see both the 60MHz and the 5.3MHz from the
>> DDS chip mixed together. My assumption is that the DDS output is
>> subtractively mixed with the 114th harmonic of the 60Mhz inside the
>> cavity: 60*114 = 6.840Ghz - ~5.3Mhz = ~6.8347 GHz clearly puts you in
>> exactly the right ballpark.
>>
>> This would also explain the very fine tuning steps - a 1Hz change on
>> the DDS output would only need a ~1.45mHz change of the unit output
>> frequency (at 10MHz) to bring the loop back into lock.
>>
>> I still have the unit with the bad Rb cell in bits, so I will have a
>> poke around it and see if I can figure out how the drive on the
>> C-Field coil is derived.
>>
>> Regards,
>>
>> Pete
>>
>>
>>
>>
>> On Sun, Nov 13, 2011 at 7:40 PM,<EWKehren at aol.com> wrote:
>>>
>>> Pete
>>> Thank you for your information. I agree with your findings and as I
>>
>> pointed
>>>
>>> out previously it support the math that the AD 9832 is used for tuning.
>>> That allows them to set the Rb at the optimum operating point based on
>>
>> their
>>>
>>> gas mixture. What I like to know is how they control the C field.
>>
>> Again I
>>>
>>> think they picked an optimum point and only vary it slightly for
>>> temperature compensation. I would like to use the C field to fine tune
>>
>> using a
>>>
>>> modified Shera controller. Latest voltage measurements on the C field
>>
>> across the
>>>
>>> coil are 2.5110 and 2.5238 down from 2.5134 and 2.5256.
>>> Bert Kehren
>>>
>>>
>>> In a message dated 11/13/2011 4:38:09 A.M. Eastern Standard Time,
>>> bell.peter at gmail.com writes:
>>>
>>> I can let you know what I've found out about these units - I got given
>>> a couple of dead ones and did a bit of poking around trying to get
>>> them working. I didn't get that far, since one of the units was
>>> easily fixed (the MAX882 3.3V regulator had failed) and the other
>>> seems to have a faulty Rb absorption cell (it works if you swap the
>>> cell from the other unit into it).
>>>
>>> The first is, as you noticed, that they have 3 voltage regulators -
>>> but apparently couldn't spare one to generate the +5V line - they seem
>>> to run (1) The Rb lamp / heater (the one nearest the connector) (2)
>>> the cell heater (the middle one) and (3) the analog electronics @8.8V
>>> (the last one).
>>>
>>> The quickest way to verify this is to apply +15V / GND to pins 1 and 2
>>> of the d-type and then check the voltage on the VCC pin (20) of the
>>> 74ACT240 buffer chip next to the connector - there is no 5V there.
>>> There is also no 5V on pin 5 of the MAX882 - and hence no 3.3V line.
>>>
>>> There is a connection between these points and pin 4 of the d-type -
>>> and applying an external +5V to this pin will bring up the 3.3V line
>>> and allow the unit to lock. When locked, pin 3 on the d-type goes
>>> low, and will sink enough current to operate an LED.
>>>
>>> Pin 5 is also connected to GND, and was (on the original PCB) also
>>> connected to the ground plane along with pin 2. It doesn't seem to be
>>> actually necessary, as the unit will operate with a single ground
>>> connection, but would it would seem to be good practice to use this
>>> pin, too.
>>>
>>> It's been alleged that pin 6 is a 1PPS output - but I can't see
>>> anything on it at all except a constant logic 1 - I tried changing the
>>> 'ACT240 in case the buffer was damaged, but this had no effect, and
>>> the pin is still a constant 1. I suppose it's possible that there is
>>> an extremely narrow -ve going pulse on it, but if there is it's too
>>> narrow for the trigger circuit on my (100MHz) scope to see it.
>>>
>>> Pin 7 outputs a 10MHz sine wave - about 800mV p-p unloaded. I haven't
>>> put it into an analyzer, but it looks pretty good.
>>>
>>> Pin 8 and 9 are connected to the MAX3232 on the board, and from them
>>> onto the serial port on the DS80C323 CPU. Pin 8 is RXD, pin 9 is TXD
>>> (from the unit's point of view). This serial port accepts the commands
>>> described in the FEI document that's floating around the net for
>>> trimming the oscillator. They appear to operate as described.
>>>
>>> Internally, the main VXCO runs at 60MHz - it's buffered and fed into
>>> the Xilinx XC9572XL PLD on the back of the board. This chip appears
>>> to contain mostly frequency dividers - it generates the 10MHz output,
>>> 20MHz for the MCLK to the DDS chip (although with a slightly nasty
>>> 40:60 duty cycle) a 416.6666Hz drive for the fselect pin on the DDS
>>> chip, a 833.33333Hz drive for the lock in amp. There are also a bunch
>>> of signals that go to the test connector, and are presumably used for
>>> factory programming.
>>>
>>> The output of the DDS is about 5.3MHz with FM on it at a 416.666Hz
>>> rate - this is mixed in with the 60MHz output from the VCXO to give
>>> the drive signal to the snap diode in the physics package.
>>>
>>> There are 3 pots on the board - the one that's normally accessible via
>>> a hole in the case seems to be intended as a C-field adjust, but does
>>> nothing on the units I have - the other one near it appears to trim
>>> something in the photocell amplifier circuit. The one on the other
>>> side of the board (near the VCXO) sets the bias on the snap diode
>>>
>>> That's all I've got, since I then worked out that I didn't have an
>>> electronics problem - hope it helps.
>>>
>>> Regards,
>>>
>>> Pete Bell
>>>
>>>
>>> On Sun, Nov 13, 2011 at 1:46 AM, Don Latham<djl at montana.com> wrote:
>>>>
>>>> I just bought a couple of 5680A's that have the same FEI p/n. They are
>>>> pop-riveted to a heavy double-sided board., obviously cut off from a
>>>> longer board. I've removed one of these from it's board/heatsink.
>>
>> There
>>>>
>>>> are two pots on the board, only one of them can be trimmed with the
>>
>> case
>>>>
>>>> on. The sinewave forming filter and maybe countdown chips are not
>>
>> there,
>>>>
>>>> and never were. There are three identical voltage regulators on the
>>>> heatsink spine.
>>>> I'll be doing some more reverse engineering on these units; they were
>>
>> so
>>>>
>>>> cheap I had to have a couple! If only FEI was more helpful! hey must
>>>> have moved on from these, and could put one manual out there?
>>>> Oh Well!
>>>> Don
>>>>
>>>> EWKehren at aol.com
>>>>>
>>>>> The FE 5680A's advertised as NEW are not NEW! A friend that made
>>>>> me
>>>>> aware of the sale did notice clear signs of use, so I did a closer
>>>>> inspection
>>>>> under a Microscope and found clear indications that the unit has
>>>>> been
>>>>> bolted down in the past. Does work fine and I am looking at ways to
>>>>> go
>>>>> directly
>>>>> to the C field to disciplin the Rb. Does any one have info that would
>>>>> help
>>>>> to do so.
>>>>> Bert Kehren Miami
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts at febo.com
>>>>> To unsubscribe, go to
>>>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>> and follow the instructions there.
>>>>>
>>>>
>>>> --
>>>> "Neither the voice of authority nor the weight of reason and argument
>>>> are as significant as experiment, for thence comes quiet to the mind."
>>>> R. Bacon
>>>> "If you don't know what it is, don't poke it."
>>>> Ghost in the Shell
>>>>
>>>>
>>>> Dr. Don Latham AJ7LL
>>>> Six Mile Systems LLP
>>>> 17850 Six Mile Road
>>>> POB 134
>>>> Huson, MT, 59846
>>>> VOX 406-626-4304
>>>> www.lightningforensics.com
>>>> www.sixmilesystems.com
>>>>
>>>>
>>>>
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts at febo.com
>>>> To unsubscribe, go to
>>>
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>
>>>> and follow the instructions there.
>>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to
>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts at febo.com
>>> To unsubscribe, go to
>>
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>
>>> and follow the instructions there.
>>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>> _______________________________________________
>> time-nuts mailing list -- time-nuts at febo.com
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
> --
> Chuck Forsberg WA7KGX N2469R caf at omen.com www.omen.com
> Developer of Industrial ZMODEM(Tm) for Embedded Applications
> Omen Technology Inc "The High Reliability Software"
> 10255 NW Old Cornelius Pass Portland OR 97231 503-614-0430
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
More information about the Time-nuts_lists.febo.com
mailing list