The suggestions you have received here are all pretty good. I would
add, however, that you ought to "just do it." These kinds of jobs,
while tedious, are often easier than you think. Just dive in, and in
an hour, or a few hours, you'll be done and can move on.
That said, I remember reading, in the early 80s about a Cray
supercomputer that contained thirty MILES of twisted pair 30 gauge
wire wrap wire, all the same color. Talk about yer nightmares.
Are the cables still connected to controls or whatever at one end? If so,
any continuity test might be confused by sneak paths through the controls
(multiple conductors will be connected through closed contacts or low
impedance relay coils).
If there are terminal blocks available, its best to disconnect one conductor
at a time and test it at the (disconnected) far end of a cable. That
doesn't take as much time as it sounds. I use a continuity tester with an
audible signal and brushing the probe over all the free conductors a few
times, listening for the beep narrows it down pretty rapidly.
Paul Hovnanian email@example.com
On Mon, 27 Sep 2010 11:19:39 -0700, "Paul Hovnanian P.E."
Yep, this is the point everybody missed. The operator panel is all
soldered up and I don't want to take anyting apart in there. it would
ruin it. I don't need to just trace a wire from one end to the other,
I need to know which wire is connected to which switch.
Well, not *everybody* missed the point.
Does your ohmmeter have a 'beep' continuity mode?
(This goes a lot faster than my explanation implies.)
Start by shorting the two probes together to confirm the
meter will beep properly.
Place one probe on pin 1 and move the other probe to pin 2 - 50
in sequence. Record all beeps. Move your probe from pin 1 to pin 2
and repeat your scan with your other probe.
If a pin beeps to any other pin, write that down.
'Pin 5 to pin 32' for example.
Eventually you will find a pin that beeps to a lot
of other pins. (Often, many of the even - numbered pins or odd -
numbered pins.) If these pins also beep to a ground point on the
control panel, you have good evidence to support the theory that
you found your ground connections.
Confirm this by switching to normal 'ohms' mode and check the
'beeping' connections once more. You should see that there is
no difference in resistance between 'shorted probes' and your
suspected connections. Remove any connection from your list that
appears to exceed that resistance by say 0.7 ohm or more.
Example: With probes shorted together, you see that the meter
reads 0.2 ohm. All the valid connections will read no more
than say 0.9 ohm. (Practically speaking, your valid readings
should also be in the 0.2 ohm - 0.5 ohm range).
A pin reading higher resistance should be dropped from your
list (unless it is just a dirty connection that you can polish
and bring under 0.9 ohm).
Use alligator clips to connect your beeping ohmmeter to your
ground connection and hold the other probe in sequence to each
of the pins that did not beep.
Press each button on the control panel till you hear your meter
beep. Write down the pin number and button logo.
You can run this inspection in about 1% of the time it would take
to build your terminal strip.
That is how I do it.
We didn't miss it, you didn't give much background detail so I posted
a generalized cable tracing procedure.
Is this unit completely passive, only lights and switches, or does it
contain active circuitry? Even relays count, coils with kickback
diodes have a polarity and you may have to energize them to find the
How easily can you connect to it? Are you holding meter probes on pins
or can you plug in a wired connector and make solid hands-free
Passive, several lamps, pushbuttons, rotary switches, and a few
toggles. One MPG (manual pulse generator - like an encoder)
Right now I have two 30' cables with an end on it that plugs into a
Fanuc 6 computer board header. The cables are at least 20' too long.
Somebody suggested all the spares are likely tied to ground. It looks
like on the computer end only. I don't have the compter here right now
and i can't find any conductors going to ground. I'll get the computer
back and focus on finding the spares first. Like somebody said, this
will cut the problem in half.
From there, I guess I'm planning on hooking each wire up to an Opto22
input. They have an LED that will light when they see power. Its only
fifty wires, once its all connected i should be able to toggle an
input and see which opto fires.
If you can put stripped, numbered wires in the mate of that Fanuc
connector you can check resistance between each wire and all the
others, clipped together.
Closed switch contacts are shorts which open when you flip that
switch, lamps should show a filament resistance. You might be able to
make them glow slightly by powering them with a battery and series
limiting resistor or light bulb. But be sure the voltage and current
from the battery won't hurt anything. A car side marker bulb might
After you marked and eliminated the bulbs and closed contacts, the
open contact wires should be easier.
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