108 S-Series Oscilloscopes Service Guide
7 Theory of Operation
Motherboard Assembly
The motherboard assembly provides all system control and interface functions for
the oscilloscope. It consists of the Windows-based motherboard, the hard disk
drive, and the bulk power supply.
Motherboard
The motherboard contains a microprocessor, a hard disk drive interface, ROM,
RAM, keyboard and mouse interfaces, connections to the front panel assembly,
and serial and parallel interfaces.
It is common for the motherboard to be revised during the life of the oscilloscope,
so if a motherboard is replaced during a repair procedure, check to make sure it
matches the image on the hard drive. It is important for the hard disk drive image
to match the motherboard. If they do not match, the oscilloscope may not have
the correct Windows software drivers.
Disk drive
The hard disk drive is a high-capacity, removable, solid state, shock-resistant unit
that stores the oscilloscope operating system, the oscilloscope application,
compliance application information, calibration data, other data files, drivers for
the boards and oscilloscope, and user data files.
The hard disk drive can also be used to store and recall oscilloscope setups and
waveforms.
Power supply
The power supply is a safety-approved +12 V bulk supply. It transforms AC power
to the main +12 V 40A supply and a 2A +5 V supply. The +5 V supply is used only
by supervisory circuits that monitor and control all other supplies. In the event of a
safety shutdown from the supervisory circuits, LEDs turn on to indicate the cause
of the shutdown. They remain lit for a few seconds until the motherboard reboots.
The +12 V bulk supply is used to create all other supplies in the instrument. +12 V
is turned on by the power switch on the front panel. It is turned off under software
control when a shutdown is requested, or by the supervisory circuits when a fault
occurs.
The oscilloscope runs from 100-120 V at AC input frequencies of 50, 60, and 400
Hz. It runs from 100-240 V at 50 and 60 Hz. Maximum input power is 380 W.
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