Chapter 8 169
Power Supply/Midplane Troubleshooting
A6 Midplane Description
A6 Midplane Description
Purpose
The Midplane links the following major assemblies:
• A3 CPU Assembly
• A5 Power Supply Assembly
• A7 Motherboard
• A9 L.O. Assembly
Refer to Figure 8-3. The Midplane Assembly (5) plugs into the Motherboard. The
CPU, Power Supply, and L.O. Assemblies plug directly into the Midplane board
from the rear of the instrument. The Digital I.F. Assemblies plug into the CXA
from the rear of the instrument into the Motherboard itself.
The Midplane Assembly itself has the following circuits:
• Power supply dithering. This triangle wave of approximately 100 Hz goes
directly to the A5 Power Supply and is used to frequency modulate the power
supply switching frequency for the purpose of lowering any power supply
related sidebands.
• +3.3 volt analog linear power supply (+3.3 A)
• -5.2 volt analog linear power supply (-5.2 A)
• Circuit to phase lock the CPU clock to the instrument's 10 MHz reference
• Non-volatile memory for storage of software license keys
• Power Supply test points and status LED's
• Complex Programmable Logic Device (CPLD) used as instrument local bus
(ILB) buffer to A9 L.O. Assembly.
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