84 Chapter 2
Block Diagrams
Miscellaneous
Miscellaneous
A14 Fan Control Board
Three fans are used to cool the various assemblies in the instrument.
The fan speed varies with internal instrument temperature; as the
internal temperature increases, the fan speed also increases. The front
panel power switch line that turns the power supply on and off is input
from the fan control board. An over-temperature circuit is provided that
will turn off the instrument if necessary.
A15 Daughter Board
The daughter board plugs into the A21 motherboard. It serves the
following functions:
• Supplies the 10 MHz reference signal to the A17 (RF), A19
(Synthesizer), A12 (Analog IF), and A18 (Frequency Reference
Assembly) boards. The 10 MHz reference signal comes from the A18
board.
• If the 1 to 30 MHz external reference is selected, the A15
daughterboard will output the external reference signal to the A18
board.
• Triggering signals for external equipment are input into the A15
daughter board.
A21 Motherboard
The A21 motherboard provides the following functions:
1. Provides a load to the power supply assembly for the +9 V, −5.2 V,
−15 V, +5.2 V supply lines. This allows a minimum set of PC board
assemblies to be present for power supply operation. See the power
supply troubleshooting section of this manual for a list of minimum
assemblies required. This will help isolate power supply problems.
2. The on/off switch is located here.
3. Provides regulated +12 V and −12 V supplies to the processor board.
4. Provides interconnections between many assemblies.
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