[time-nuts] FTS-4060M/S24

Mark Sims holrum at hotmail.com
Thu Jun 19 18:54:06 EDT 2008


I recently bought a FTS-4060M/S24 cesium beam unit.  It is a rather stripped down model,  with 1MHz on the front panel and only 1/5/10MHz/Fault BNC's on the back (does not even have the monitor port on the back).

It looks like the tube is good.  I can scan though the resonance peaks.  Turning MOD off changes the beam current, etc.  I am pretty sure I have the control voltage properly centered and think I may have the beam current centered (no way to tell for sure since I can't find that mysterious E26 test point).  No telling how long it was in storage.  It was made in 1987.  The beam current seems to jitter around 1 meter tick.  I've had it on about 48 hours now.

There are a few issues with it.  First the crystal oven monitor reading stays at 5V.  The unit has an FTS-2000A OCXO.  This is basically a smaller OCXO that is mounted on a carrier and has a small connector PCB attached that converts the pinouts to match the Datum 1000 OCXO.  The OCXO does seem to stabilize at the proper freq.  All the other monitor voltages seem OK.

Second,  when powered up the unit seems to not perform the auto alignment.  The control voltage stays at 5V.  You can manually force it to start aligning (LOOP off,  ALARM+ALIGN buttons,  ALIGN,  LOOP on).  This also turns on the ALARM light.  You can get it out of ALARM mode by (LOOP off,  ALARM+ALIGN,  LOOP on,  ALARM).

Third,  the unit never displays LOCK and the ALIGN light never goes out.  It does appear to either be locked or close to lock.  The output tracks a Thunderbolt +/- 1nS (the resoultion of my current counter) over long enough periods (l24 hours) of time to probably rule out OCXO holdover performace.

Any ideas?

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