Installation guide

Troubleshooting
Troubleshooting Unlocks
1-72
623 Demod Unlock
A 623 Demod Unlock message indicates a problem with the Voltage Control Oscillator’s (VCO) phase-lock loop
on the A9 Digital Demodulator (Option 501, 502, 503, 504 with Option 300).
❏ Check the 10 MHz signal on the A23 Motherboard at J2 pins 26 and 91 using an oscilloscope.
The signal period should be 100 ns with an amplitude of approximately 1.0 Vp-p or greater.
— If the signal is good, replace the A9 Digital Demodulator (Option 501, 502, 503, 504 with Option 300).
(Refer to “A9 Digital Demodulator (Option 501, 502, 503, 504 with Option 300)” on page 2-24.)
— If the signal is bad, troubleshoot one of the following two assemblies:
— either the A23 Motherboard
(Refer to “Self-Tests 21xx for the A23 Motherboard” on page 1-66.)
— or the A18 Reference
(Refer to “Self-Tests 8xx for the A18 Reference” on page 1-50.)