Cisco GS7000 Operating instructions

Troubleshooting
This troubleshooting section lists common problems and their solutions. If a troubleshooting procedure directs
you to replace a module of the 1.2 GHz GS7000 Remote PHY Device (RPD) 2X2 Segmentable Node, see
Removing and Replacing Modules.
•No RF Output at Receiver RF Test Point: Optical Power LED on Receiver Module is off, on page 1
•No RF Output: Fiber Optic Light Level is Good, Receiver Optical Power LED is on, on page 3
•Poor C/N Performance, on page 4
•Poor Distortion Performance, on page 6
•Poor Frequency Response, on page 8
•No RF Output from Reverse Receiver, on page 9
•Reference: 2x2 RPD Module LEDs, on page 10
No RF Output at Receiver RF Test Point: Optical Power LED on
Receiver Module is off
Follow this troubleshooting flowchart. Also see the notes following the chart.
Troubleshooting
1

These notes apply to the previous troubleshooting flowchart.
DescriptionNote
For low input receiverFor standard receiver
This unit will have no RF output.This unit will have no RF output.1
The receiver will not function below this DC
level which is equal to -10 dBm.
• The optimum light level input is -10 to -2
dBm.
• For every 1 dBm change in optical input
power, the RF output will change by 2 dB.
• Excessively high light input levels (> -2
dBm) will cause distortions and/or damage
the photo diode.
The receiver will not function below this DC
level which is equal to -10 dBm.
• The optimum light level input is -6 to 2
dBm.
• For every 1 dBm change in optical input
power, the RF output will change by 2 dB.
• Excessively high light input levels (> +2
dBm) will cause distortions and/or damage
the photo diode.
2
Troubleshooting
2
Troubleshooting
No RF Output at Receiver RF Test Point: Optical Power LED on Receiver Module is off

No RF Output: Fiber Optic Light Level is Good, Receiver Optical
Power LED is on
Follow this troubleshooting flowchart. Also see the notes following the chart.
These notes apply to the previous troubleshooting flowchart.
Troubleshooting
3
Troubleshooting
No RF Output: Fiber Optic Light Level is Good, Receiver Optical Power LED is on

DescriptionNote
For low input receiverFor standard receiver
If the green LED is Off, it is outside optical
input range. Green (On) indicates that light is
present and the optical input value is higher than
-14 dBm.
If the green LED is Off, it is outside optical
input range. Green (On) indicates that light is
present and the optical input value is higher than
-10 dBm.
1
The recommended RF output level at the output
of the receiver module is 27 dBmV (+7.0 dBmV
as measured at the -20 dB RF test point). This
setup is recommended to achieve the best
possible performance with 8 dB setting.
The recommended RF output level at the output
of the receiver module is 27 dBmV (+7.0 dBmV
as measured at the -20 dB RF test point). This
setup is recommended to achieve the best
possible performance.
2
• Assumes 2.5% OMI/CH or 20% composite.
• Assumes 1310 nm wavelength / Add one dB for 1550.
• Assumes 0dB attenuator switch setting unless noted, if otherwise subtract attenuator value from reading.
• Assumes -4dB optical input, if otherwise add or subtract 2dB RF for each 1dB optical input.
Note
Poor C/N Performance
Follow this troubleshooting flowchart. Also see the notes following the chart.
Troubleshooting
4
Troubleshooting
Poor C/N Performance

These notes apply to the previous troubleshooting flowchart.
DescriptionNote
RF drive level to the laser must be set to the laser manufacturer’s specification.1
It is possible that the distribution module is set up incorrectly. See the pad and equalizer selection
charts in Appendix A for correct pad and equalization. The C/N performance will suffer if the
RF levels are too low into the first gain stage or the interstage.
2
Troubleshooting
5
Troubleshooting
Poor C/N Performance

DescriptionNote
It is important to monitor the DC level at the receiver module because in the process of cleaning
the connectors, the transfer of light through each connector may improve or degrade. The DC
reading should degrade if there is a reflection in the path depending on the severity of the core
mismatch. Scratches on the surface of the fiber of the connector can cause reflections. Scratched
connectors must be replaced.
3
For low input receiver
For standard receiver4
Attenuate the light to simulate the amount of
light that should be at the node and rerun the
C/N performance. Add components into the
path one at a time until the problem is found.
Change jumpers, couplers, fibers and connectors
one at a time, taking C/N measurements after
each change.
A phenomenon called “shot noise” will occur
if the light level is too high into the receiver.
This is noise generated by the photo diode when
the light is converted back to RF. An optical
input level exceeding -2 dBm at the detector
will also generate distortions.
Attenuate the light to simulate the amount of
light that should be at the node and rerun the
C/N performance. Add components into the
path one at a time until the problem is found.
Change jumpers, couplers, fibers and connectors
one at a time, taking C/N measurements after
each change.
A phenomenon called “shot noise” will occur
if the light level is too high into the receiver.
This is noise generated by the photo diode when
the light is converted back to RF. An optical
input level exceeding +2 dBm at the detector
will also generate distortions.
• Assumes 2.5% OMI/CH or 20% composite.
• Assumes 1310 nm wavelength / Add one dB for 1550.
• Assumes 0dB attenuator switch setting unless noted, if otherwise subtract attenuator value from reading.
• Assumes -4dB optical input, if otherwise add or subtract 2dB RF for each 1dB optical input.
Note
Poor Distortion Performance
Follow this troubleshooting flowchart. Also see the notes following the chart.
Troubleshooting
6
Troubleshooting
Poor Distortion Performance

These notes apply to the previous troubleshooting flowchart.
DescriptionNote
Recommended RF input levels are:
• Headend transmitter module: 14 dBmV
Based on 79-channel loading. The input will increase as the channel loading decreases.
Note
1
Troubleshooting
7
Troubleshooting
Poor Distortion Performance

DescriptionNote
For low input receiver
For standard receiver2
The range for optical light input level is -10 to
-2 dBm which converts to 0.1 to 0.6 V DC. The
optimum operating range is -6 dBm to -2 dBm
which converts to 0.25 to 0.6 V DC. Levels
higher than -2 dBm can cause the photo diode
to generate distortions, which add to the
distortion performance of the link, effectively
degrading the distortion performance.
The range for optical light input level is -6 to
+2 dBm which converts to 0.25 to 1.6 V DC.
The optimum operating range is -3 dBm to +2
dBm which converts to 0.5 to 1.6 V DC. Levels
higher than +2 dBm can cause the photo diode
to generate distortions, which add to the
distortion performance of the link, effectively
degrading the distortion performance.
Attenuate the light to simulate the amount of light that should be at the 1.2 GHz GS7000 Node
and rerun the distortion performance. If the distortion performance improves, there is too much
light. An inline optical attenuator or a coupler with a higher loss can reduce the light, or the laser
may have to be replaced with a lower launch power.
3
Attenuate the RF input level into the amplifier by increasing the pad value at the OIB. If the
distortion perform improves, there is too much RF.
4
Poor Frequency Response
Follow this troubleshooting flowchart. Also see the notes following the chart.
Troubleshooting
8
Troubleshooting
Poor Frequency Response

These notes apply to the previous troubleshooting flowchart.
DescriptionNote
Be sure all unused ports are properly terminated into 75 ohms to prevent mismatches. The
frequency response is cumulative and reflects the response of each active device in the link:
• The frequency response for the transmitter is dependent on the transmitter manufacturer's
specification.
• The frequency response of the node is ±1.0 dB from 52 MHz to 1218 MHz (for optical
receiver and amplifier combined).
1
It is possible that the RF amplifier is set up incorrectly. Always check to see that padding and
equalization is correct to ensure proper levels at the inputs to each gain stage. See the pad and
equalizer selection charts in Technical Information for correct pad and equalization.
2
No RF Output from Reverse Receiver
Follow this troubleshooting flowchart.
Troubleshooting
9
Troubleshooting
No RF Output from Reverse Receiver

Reference: 2x2 RPD Module LEDs
This section contains LED definition for the 2x2 RPD module. It provides a coarse-grained indication of
device connectivity to field technicians during their installation or repair of the RPD.
NotesState IndicatedLED Pattern or ColorLED
Required - Indicates power goodPower-on - InitializingGreen - 2 Hz Flash
Pattern
System
LEDs
Required - Indicates remote SSHv2 session
possible
IP acquired via DHCP,
synchronizing and acquiring
configuration
Green - 4 Hz Flash
Pattern
No faults detectedSystem status good -
Connections good
Green - Steady
Loose connection, connector faults, water
ingress at connector, wavelength mismatch,
etc.
Connection fault - No physical
connection to CIN or RF
interfaces
Red - 2 Hz Flash
Pattern
Wrong DHCP configuration, unreachable
hosts, failed authentication with CCAP
Core, etc.
Configuration fault - Failed
synchronization or failed to
receive configuration from
Principal CCAP Core
Red - 4 Hz Flash
Pattern
Indicates hardware fault, always indicated
by a steadily illuminated LED.
System fault - Device cannot
initialize
Red - Steady
Vendor-defined LED behavior. May
indicate high error rates in CIN or RF
ports, marginal operating conditions, etc.
Warning - RPD operational but
operation is imperfect
Amber - Various
Indicates connection state
Per [IEEE 802.3x]Flash PatternCIN
LEDs
Indicates possible port failure or a port
which has been configured to be disabled
Ethernet port failure or port
administratively disabled
Unilluminated
At least one pilot and/or alignment tone
active
Power-on - Downstream RF
initializing
2 Hz Flash PatternD-RF
LEDs
Awaiting downstream channel set
configuration
Channel or channels activated4 Hz Flash Pattern
Downstream channels operationalDownstream channel set
configuration obtained
Steadily Illuminated
Fault detected in RF port or RF port muted
by CCAP Core
RF port fault or RF port muteUnilluminated
Troubleshooting
10
Troubleshooting
Reference: 2x2 RPD Module LEDs