[time-nuts] FE 5680A Warning

Pete Lancashire pete at petelancashire.com
Sun Nov 13 13:30:12 EST 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
>>>>
>>>>
>>>>
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>>>>
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>
> --
> 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
>
>
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