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Troubleshooting
Troubleshooting Unlocks
Troubleshooting Unlocks
The phase lock loop refers to 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 frequency 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 signals are slightly out of phase,
the phase comparator circuit adjusts the frequency loop signal until the two 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.
There are four phase lock circuits in the frequency generation loop that can generate error
messages. These phase lock loops are located on the A6 Frac–N, A5 Sampler, and A7 Reference.
There is also one other phase lock loop on the A11 Pulse/Analog Modulation Generator that can
generate an error message when the signal generator is in phase modulation mode.
508 A6 Frac–N Loop Unlock
A 508 Frac–N unlock message indicates a failure of the A6 Frac–N.
1. Check P33–15 on the A31 Motherboard for the 10 MHz sync. approximately 2 V
pp
.
2. If the signal is present replace the A6 Frac–N.
3. If the signal is not present, troubleshoot back to the A7 Reference.
513 1 GHz Out of Lock
A 513 1 GHz Out of Lock message indicates a failure on the A7 Reference.
• Replace the A7 Reference.
514 Reference Oven Cold
The Reference Oven Cold Error message indicated the reference has not been connected to electrical
power for 30 minutes. This message appears when the signal generator is unplugged or the
reference assembly is removed. The message is controlled by a timer and should turn off after 30
minutes. This is not a failure unless the message does not go off after 30 minutes. If it continues to
be displayed after 30 minutes, replace the A7 Reference.
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