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Square wave signal restored by resistor

gunship800

Jul 20, 2012
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20221130_185946.jpg

A square wave signal failed for whatever reason. Installing a 1k ohm resistor across the signal and 12+ restored the signal again. What's the electronic theory behind this, or how did it repair whatever failed? What failure point should I look for inside the unit that caused this?
 

Harald Kapp

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Nov 17, 2011
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What's the electronic theory behind this,
That depends on what you mean by
A square wave signal failed

Possibly the signal was deteriorated by rounded edges (no longer square) due to capacitive loading (e.g. long wires) and the sources driving capability not being a match to charge this capacitance quickly. By adding a pull-up resistor you assist the driver in pulling the line high (towards 12 V). You thus restored the "squareness" of the signal up to a point where it is recognized by the receiver.

Not much more to analyze without knowing more details about the circuits and possibly seeing oscilloscope diagrams of the signal before and after adding that resistor.
 

danadak

Feb 19, 2021
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Output circuit is an open drain circuit that discharged parasitic C so
output decayed quickly and w/o pullup never could show a high level
again without it ?

1670157881216.png

Just a thought.


Regards, Dana.
 

davenn

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Sep 5, 2009
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View attachment 57149

A square wave signal failed for whatever reason. Installing a 1k ohm resistor across the signal and 12+ restored the signal again. What's the electronic theory behind this, or how did it repair whatever failed? What failure point should I look for inside the unit that caused this?

Your post is severely lacking info with which to help you
Danadak has had a good guesstimate but without further info from you, it's impossible to help further

WHAT is in the box on the left ? what is it ? show photos, part numbers etc
 
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