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WARNING: Disconnect primary power prior to servicing.
Operator Guide
3.5 Emergency Operating Procedures
3.5.1 Multiple PA Failures in a Foursome
!
WARNING:
THE PA MODULES ARE DESIGNED TO HANDLE VERY HIGH TEMPERATURES
AND MAY BE EXTREMELY HOT. DO NOT TOUCH THE MODULES WITH BARE
HANDS AFTER THE TRANSMITTER HAS BEEN RUNNING, ESPECIALLY IN HIGH
AMBIENT TEMPERATURE ENVIRONMENTS.
If two PAs were to fail in a single group of four or Foursome, the resulting system
imbalance could result in a power foldback to approximately 84% of nominal power
output. Since a single PA failure in a foursome does not create an imbalance severe
enough to cause foldback, one of the PA modules with a bad PA should be taken
out, turned over and re-inserted, placing the bad PA in a different foursome. For
example, if PA amplifiers B1 and B2 have failed, pull out the A2/B2 PA module,
turn it over and plug it back in so that the bad PA is in position A2 instead of B2.
There are still 2 failed PAs, B1 and A2, but now each one is in a different foursome.
This will restore balance to the system and the transmitter will still be able to
operate at or near full power output by automatically increasing the drive to the
remaining PAs (via the APC voltage). For more information on Foursomes refer to
Section IV, Overall System Theory, under the heading “8-Way Combiner”.
For quick reference, the foursome groupings are as follows:
(See Figure 4-5 and Figure 4-6 on page 4-12)
• A1, A2, A3 and A4 - Front Right Foursome
• B1, B2, B3 and B4 - Front Left Foursome
• A5, A6, A7 and A8 - Rear Left Foursome
• B5, B6, B7 and B8 - Rear Right Foursome
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