HP 30242 Installation And Service Manual page 38

Principles of Operation
MAU PO'VER CONTROL CIRCUIT. The MAU power control circuit provides three functions:
12-Volt Switch
The Z- 8 OB MPU can turn the 12V to the AUI on or off.
12-Volt Current Protect
If the current to the AUI goes above 1.
2A, the power control circuit causes the + 12V to turn off, thus
protecting the LANIC and the system from shorts in the AUI cable or the MAU. The Z-80B will
detect the fault and attempt to restart MAU power. If the attempt fails, the Z- 80B notifies the host
system of the fault.
12-Volt Sense
The Z-80B can determine if power to the AUI is on or off. However, it is not able to accurately
measure the exact voltage being supplied. The IEEE 802. 3 standard requires VP
(+
12V) to be greater
than 11. 28 volts. It is possible that the + 12-volt power supply may be adjusted low enough such that
less than 11. 28 volts is present at the LANIC edge under load. This will cause difficulty for the
HP
30241A MAU only when AUI cables near the maximum length are used. If faulty MAU operation is
suspected, and MAU replacement has not corrected the problem, the VP voltage should be checked.
The VP voltage can be checked by attaching an accurate voltmeter between the + 12V and GNO test
points on the LANIC. If the voltage under load is found to be less than 11. 28V, the system + 12V
power supply must be checked and adjusted to the upper end of the allowable range. If the power
supply is already set at the upper end of its range, the LANIC may need to be replaced. Consult the
appropriate
CE Handbook
for details.
LEOs.
The LANIC uses 15 LEDs to monitor activities on the card and the LAN network. The locations of the
LEOs are shown in Section 2, figure 2-1; the labels and functions of the LEOs are shown in figure 3-3.
The seven LEOs labeled A through G monitor activity on the AUI interface. The eight LEDs labeled H
through Nand
*
monitor LANIC MPU activity. A great deal of information about the state of the
network and the LANIC and system software can be gained by studying the LEOs. They are provided as
an aid in problem detection and resolution.
Each of the 15 LEOs is labeled with two different labels. The single alphabetic labels are helpful for
quick reference to the LEDs; the two-letter mnemonics are intended to remind users of the function
being indicated by the LED.
Feb 85
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