Service manual
Circuit Descriptions
3-2
Power-off
The power-off sequence is software controlled. The power-off sequence is initiated when
the key is pressed, battery time-out occurs, or the battery is too low to
continue. At power-off, the software begins housekeeping tasks such as turning off the
printer, disabling the keyboard, and turning off the display, if present. When the
housekeeping is complete, the software instructs the System Gate Array to turn off the
Switched 5V supply. The details of how the power supply shuts down are described later
in this chapter in the power supply description.
2Circuit Descriptions
The M177XA family of cardiographs has a common set of major subassemblies: a Power
Supply board, a CPU Assembly board, and a Keyboard (including a Display on the
200/200i/300pi). The design also includes a thermal print mechanism. The power supply
design requires a battery for all operations. Option #A05 adds a storage and transmission
board.
Option #A10 adds an interface board for communication to the HP StressWriter system.
The CPU assembly is the same for all cardiographs except that some models of the
PageWriter 200/200i CPU assembly have an extra ROM to accommodate the ECG
measurements and interpretation software. The subassemblies, including the CPU
assembly and its major circuit groups, are shown in Figure 3-1.
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