[time-nuts] FE-5680 frequency jump

[Bob Quenelle]

I’ve been running an FE-5680 for maybe a total of 50 hours over the last several months.  I found that an offset setting of 180 made it track GPS and (previously-set) LPRO-101 10 MHz signals.  Even with power cycling, after about 1/2 hour, with an offset setting of 180 the FE-5680 was stable.  The last time I turned on the FE-5680, it drifted with a setting of 180 and needed a new setting of –415 to track the other signals.  That’s a change of 595 counts and with a resolution of 6.8 uHz per count, a frequency change of 4 mHz (0.004 Hz) and 0.4 ppb.   Operation at the new setting is stable for now.  The lock signal indicates lock and the power supply voltage is still 15V.  I haven’t checked lamp voltage or VCXO voltage as that requires opening the case. 

Before I start poking around, thought I’d ask if anyone has seen a similar symptom.  Time to open it up?

Thanks,
Bob