Section 6 - Maintenance And Troubleshooting; Periodic Maintenance; Clock Adjustment; Troubleshooting - Radyne DMD20 Installation And Operation Manual

DMD20 Universal Satellite Modem
Section 6 – Maintenance and Troubleshooting
This section discusses unit maintenance and troubleshooting for the DMD20 Universal Satellite
Modem.
The DMD20 contains a Lithium Battery. DANGER OF EXPLOSION exists
if the battery is incorrectly replaced.
equivalent type recommended by the manufacturer.
batteries in accordance with local and national regulations.

6.0 Periodic Maintenance

There is no external fuse on the DMD20. The fuse is located on the power supply assembly
inside the case, and replacement is not intended in the field.

6.0.1 Clock Adjustment

The DMD20 allows for internal VCO speed adjustment from the front panel. Clock adjustment
should be performed only when an internal clock source has insufficient accuracy for the custom
modem application.

6.1 Troubleshooting

Should a unit be suspected of a defect in field operations after all interface signals are verified,
the correct procedure is to replace the unit with another known working DMD20. If this does not
cure the problem, wiring or power should be suspect.
The following is a brief list of possible problems that could be caused by failures of the modem or
by improper setup and configuration for the type of service. The list is arranged by possible
symptoms exhibited by the modem.
Symptom
The Modem will not
acquire the incoming
carrier:
TM103 – Rev. 1.1
Possible Cause
There is an improper receive
input to modem.
The Receive Carrier Level is too
low.
Maintenance and Troubleshooting
Replace only with the same or
Dispose of used
Action
Check that the Receive Cabling
is correct.
Check the following:
The Receive Cabling is correct.
The downconverter is properly
set and that the LNA is turned
on.
Use a spectrum analyzer to
locate and measure the Receive
Level, which should not be below
-65 dBm absolute (-50 dBm is
nominal).
6-1