Operation 27
CG635 Synthesized Clock Generator
Table 17: Troubleshooting Tips
Symptom Resolution
STOP LED flashing and output
not oscillating
Output is in stopped state. To put back into running
state, sequentially press ‘SHIFT’, ‘RUN’
CMOS output not oscillating
The front-panel CMOS output is forced to a low
state at frequencies above 250 MHz. Try setting the
frequency below 250 MHz.
RS-485 output not oscillating
The rear panel RS-485 output is disabled above
105 MHz. Try setting the frequency below
105 MHz.
PRBS outputs not functioning
Make sure PRBS is enabled. Press ‘SHIFT’,
‘PRBS ON’ to enable. The PRBS is also disabled
above 1.55 GHz. Try setting the frequency below
1.55 GHz.
UNLK LED flashes once a
second
An optional rubidium oscillator is installed but it is
not yet stable. Wait 10 minutes to give the
rubidium time to warm up and stabilize.
No GPIB communication
Check that GPIB communication is enabled.
Sequentially press ‘SHIFT’, ‘GPIB’, ‘Hz’. Also
check that the GPIB address is set correctly. See
the ADDRS secondary function.
No RS-232 communication
Check that RS-232 communication is enabled.
Sequentially press ‘SHIFT’, ‘RS-232’, ‘Hz’. Also
check that the communication parameters are set to
9600 baud, 8 bits, no parity, one stop bit and
RTS/CTS hardware flow control. When connecting
to a PC, make sure you are using a standard PC
serial cable, not a “null-modem” cable.
Doesn’t respond to key presses
and REM LED is on
The CG635 has been placed in remote mode by the
GPIB bus. Press ‘STEP SIZE’ to put the CG635
back into local mode.
ERR LED flashes
The CG635 has received characters over the
remote interface, but the command parser has
determined that the command is invalid. Check the
command syntax and make sure you are appending
a command terminator.
