[time-nuts] One sure way to kill your FE-5680A or FE-5650A

Skip Withrow skip.withrow at gmail.com
Tue Jun 7 17:22:13 EDT 2016

We recently had a customer that purchased an FEI FE-5650A (basically a
repackage version of the FE-5680A) and reported that it worked for several
hours, then died.  We promptly sent another unit, and he reported that it
died as well.  He had nothing but power hooked to the unit.

On return of the first unit, it was examined and found to have corrupted
code.  The corrupted code problem was thought to be associated with doing
bad things to the serial port (like framing errors), and we still believe
this to be the case.  However, the customer said only power was connected
to the unit.

I was asking some questions about how he was powering the unit, when he
said he turned on the power supply (a large HP variable supply) and turned
the voltage up to +15V (our 5650's are single supply).  Ah hah, slowly
ramping the voltage up on these oscillators appears to be a no no.

The second oscillator has now been examined and it too was confirmed to
have corrupted code.  So, the word of warning is - DO NOT slowly ramp the
supply voltage of FE-5680A and FE-5650A oscillators.  I can't say what
slowly is, but this guy was good at killing them.  If I get some time I may
try to repeat the results.

My advice was to set the supply at 15V and just turn it off and on.  I have
not heard from him since.

If anyone out there has a 5680A or 5650A that does not lock, the code issue
is very likely the problem.  I have seen several 5680 units as well as a
few 5650 units with this problem.  The good news is that they can be
fixed.  I would happily do this for any time-nut that has one if return
postage is included with the unit.  The bad news is that we don't know the
nature of the code problem that trashes the software (stack overflow, error
handling routine, etc.) so units can only be restored to their original
condition that still has the bug in the code.

Otherwise, the 5650 and 5680 are great values to get rubidium performance
at very reasonable prices.  I have 1000's of hours on them and 100's of
power cycles, with a lot of serial port use, so if treated correctly they
are reliable units.

Skip Withrow
RDR Electronics, Inc.


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