Installation guide

Troubleshooting
Troubleshooting Unlocks
1-68
Troubleshooting Unlocks
The phase lock loop refers to that part of the frequency generating circuit used to maintain the phase
relationship between the frequency generation loop and a reference frequency. By maintaining the phase
relationship, the frequency accuracy of the signal generator is guaranteed.
To maintain accuracy, the phase lock loop compares the phase of a signal from the reference assembly to the
phase of the frequency loop signal. If the two signals are slightly out of phase, the phase comparator circuit
adjusts the frequency loop signal until the signals are in phase. If the phase comparator circuit cannot adjust
the phase of the frequency loop signal to agree with the reference signal, the phase comparator rails and
generates an unlocked message. The unlock message is immediately displayed on the front panel display.
Troubleshoot multiple Loop unlock messages in the following order:
1. “514 Reference Oven Cold” on page 1-68
2. “515 10 MHz Signal Bad” on page 1-68
3. “512 Reference Unlocked” on page 1-69
4. “513 1 GHz Out of Lock” on page 1-69
5. “508 Frac-N Loop Unlock (Option 501, 502, 503, 504)” on page 1-69
or “508 Frac-N Loop Unlock (Option UNJ and Option 506)” on page 1-69
6. “520 Sampler Unlocked (Option UNJ and Option 506)” on page 1-70
7. “521 YO Loop Unlocked (Option UNJ and Option 506)” on page 1-71
8. “516 Baseband Generator Unlock” on page 1-71
9. “623 Demod Unlock” on page 1-72
514 Reference Oven Cold
A 514 Reference Oven Cold message indicates that the reference has not been connected to electrical power
for 5 minutes. This message appears when the signal generator is unplugged or the A18 Reference is
removed. The message is controlled by a timer and should turn off after 5 minutes. This is not a failure unless
the message does not go off after 5 minutes.
❏ Check that the message goes away after 5 minutes.
— If the message continues to be displayed after 5 minutes, replace the A18 Reference.
(Refer to “A18 Reference” on page 2-42.)
515 10 MHz Signal Bad
A 515 10 MHz Signal Bad message indicates a problem with the output of the 10 MHz reference oscillator on
the A18 Reference.
❏ Check the display for this unlock message.
— If the message is present, replace the A18 Reference.
(Refer to “A18 Reference” on page 2-42.)