This log summarises the documents I have found about the FE-5680 family.

• The auction: http://www.ebay.com/itm/301905937814
  (the provided informations are not well organised but they can be somehow understood)
• The manufacturer: http://freqelec.com/rb_osc_fe5680a.html (no useful info there)
• Some threads where this unit is examined: http://www.eevblog.com/forum/testgear/fe-5680b-1pps-to-10mhz/
• Clint's inspiring hacks : http://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.html
• EEVblog#236 - FE-5680A Rubidium Standard Teardown (there are a few other 5680-related videos on youtube, have a look)
• Some appearances in the time nuts forum https://www.febo.com/pipermail/time-nuts/2015-September/094009.html
• http://time-nuts.febo.narkive.com/0Fm6P0bH/fe-5680a-1-pps-photo
• https://drive.google.com/file/d/0B9NVwHoWDHKMWklwcU5qQlBtc2c/view?usp=sharing
  The references lead to other resources !
  http://gerrysweeney.com/build-a-10mhz-rubidium-frequency-standard-and-signal-distribution-amp-for-my-lab/
  http://www.rhodiatoce.com/pics/time-nuts/FE-5680A/FE-5680A_schematics_v0.1.pdf
  http://www.wa6vhs.com/Test equipment/FREQUENCY STANDARDS/FE-5680A/5680 TECH MANUAL.pdf