The TS-450/690 may not calibrate properly against WWV (JJY) when using
the calibration cable that is supplied with early versions of these sets,
(Serial numbers below 311XXXX) and when an antenna that is shorted for
DC is used. A dipole with a balun is a prime example of DC shorted antenna.
This failure is antenna specific; i.e. multiband beams and other similar
antennas do not cause this failure.
A new calibration cable is available that provides proper DC isolation.
Failure to use the new style cable will result in a PLL unlock condition
when calibration is attempted. A temporary countermeasure that can be used
until the new cable is obtained is to use a two conductor shielded wire.
A minor circuit modification that adds a 100 pf isolation capacitor should
also be performed. Please refer to the diagrams below for modification notes.