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Archived: External Power Supply with PB8H SSR Backplane Causes LEDs to be Half-Lit When Computer is Off

This document has been archived and is no longer updated by National Instruments

Hardware: Signal Conditioning Other>>SSR Series

Problem: The PB8H (70RCK8) SSR backplane shows the current state of the DAQ board's digital lines. When the board is connected to the computer's 5 V line, the LEDs turn off when the computer turns off. But when an external power supply is connected, they are half-lit when the computer is off, and then work properly when it is powered on.

Solution: This is correct behavior. When the board is off, the lines are in a high impedance state. The LEDs are accurately reflecting the state of the digital lines when the computer is off--their state is indeterminate.

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Report Date: 12/17/1998
Last Updated: 10/15/2003
Document ID: 1GGEOELL

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