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5.3
OSCILLOSCOPE TESTING
North Star HSIO-4
If all four I/O ports fail to communicate
with peripheral devices or fail to pass the
HSIO-4 test, this indicates that the problem
is probably in the power circuitry or the Baud
Rate Generator circuitry. The following
procedure for checking this circuitry requires
the use of an oscilloscope with a bandwidth of
at least 10 Megahertz.
The screw and nut on the top regulator
in the upper left corner (on the
component side of the board) are NOT
at ground potential and should not be
used for oscilloscope or meter
grounds, as this may damage the HSIO-4
board or the HORIZON motherboard.
1.
Turn off the computer.
2.
Place the HSIO-4 board on an extender
board, and turn on the computer. Check for
the following DC voltages:
+5 volts at pin 14 of the 1489 at 8A
+12 volts at pin 14 of the 1488 at 7B
-12 volts at pin
3.
Trace the source of the clock pulses from
pin 49 of the motherboard to the various
signals used to provide baud rates. If the
signals are not as listed in Table 5-1,
refer to the schematic drawings and trace
backward to locate the problem.
71
WARNING
1 of the 1488 at 7B
User/Technical Manual
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