Fluke 5500A, Service Manual

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5500A
Service Manual
2-8
2-7. Main CPU Assembly (A9)
The Main CPU (A9) attached to the rear panel assembly communicates with the
following assemblies:
•
Inguard CPU on the DDS assembly (A6)
•
Display assembly CPU
•
Serial and IEEE interfaces
•
External amplifier (5725A)
The main CPU memory is Flash ROM.
Each analog assembly has the same bus structure:
•
One or more Chip Select lines
•
Common data bus that connects to the motherboard, latched in by latches
•
A Fault line that sets all modules to a safe state in case of malfunction
Signals to the front panel jacks are routed by output relays on the motherboard.
2-8. Power Supplies
AC line voltage is applied through a line filter to a power module in the rear panel that
provides switching for four line voltages. The outputs of the power module are wired
directly to the primaries of the mains transformer. The safety ground wire is attached
from the power module to the rear panel.
Major internal grounds are SCOM, which is tied to OUTPUT LO and the guard shell,
ICOM, which is the internal ground for the current function, and GCOM, which is the
outguard common and is tied to earth ground.
2-9. Outguard Supplies
The motherboard generates the outguard power supplies: +12VG, -12VG, and +5VG. All
the transformer connections for the outguard supplies come through one bundle of wires
connected to the motherboard with P1. A row of test points is provided in front of the fan
for the raw and regulated supplies. The supplies are fused on the motherboard. It is
unlikely the fuses will blow unless there is another fault since the regulators will current
limit below the fuse ratings. The outguard supplies are used only by the CPU assembly
(A9) and Encoder (A2) assemblies.
2-10. Inguard Supplies
The inguard supplies are located on the Voltage assembly (A8). The transformer
connections (inguard SCOM referenced) are connected to the Motherboard (A3) via
J209. Fuses for each of the supplies are located on the Motherboard. It is unlikely the
fuses will blow unless there is another fault since the regulators will current limit below
the fuse ratings.
Filter capacitors for the high-current supply for the Current assembly (A7) are located
on the Filter assembly (A12).
The inguard SCOM referenced supplies are +15 V, -15 V, +5 V, -5 V, and +5RLH. The
+5 V and +5RLH supplies share the same raw supply. The +5RLH supply is used
exclusively as a relay driver and is nominally about 6.3 V. Test points for these supplies
are located in a row across the top of the Voltage assembly. The 65 V supplies are
rectified and filtered on the Motherboard but regulated on the Voltage assembly (A8).