G8MNY  > TECH     01.07.25 07:00z 67 Lines 2600 Bytes #199 (0) @ WW
BID : 35869_GB7CIP
Read: GUEST
Subj: Wiring & Form Tapping out
Path: ED1ZAC<ED1ZAC<GB7CIP
Sent: 250701/0653Z @:GB7CIP.#32.GBR.EURO #:35869 [Caterham Surrey GBR]
From: G8MNY@GB7CIP.#32.GBR.EURO
To  : TECH@WW

By G8MNY                                     (New Aug 07)
(8 Bit ASCII graphics use code page 437 or 850, Terminal Font)

Here is some basic methods of tapping out/fault finding wires in large
multicore cables or forms (car looms?).

DC BUZZER
If full DC access is easily available then a simple DC buzzer test will do OK.

                      Large cable
       Selected wire ððððððððððððð   Buzzer³
                ÚÄÄÄÄððððððððððððð<ÄÄÄ[]ÄÄÄ´ÞÄ¿batt
                ³    ððððððððððððð         ³  ³
                ³                             ³
     Return pathÀÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÙ
    via earth/sheath/spare wire.

For in between connectors a Pin can be inserted into single wires to make
connection to confirm the identity or prove the fault, but doing so will damage
the insulation!

UNBALANCED AC TESTING
When no access to the wire is possible then AC testing can be done with a large
AF signal and sensitive AF Amp and headphones as the phone engineers use..

                      Large Cable
       Selected wire ððððððððððððð Probe    Amp
               oÄÄÄÄÄðððððððððððððÀ=========´>ÄÄÄÄo Detecting
Series Headphone)    ððððððððððððð  Screen ³ ³     )Headphone
               o                     Lead  ³ ³    o 
 1kHz osc ÄÄÄÄÄÙ                           ÀÄÁÂÄÄÄÙ
      _³_                                    _³_
      ///                                    ///

Here the cable is not in audio pairs, the return path is via earth. The probe
is just an unscreened wire/rod connected to a short screened lead to the Amp.
The Amp is very high gain (10,000x e.g. a 741) & tailored for 1kHz.

The osc can be a steady tone or a pulsed tone, 3V AC is a good level to use.

When you hear the loudest tone in the detecting headphone from the cable, earth
that lead, and if the tone then goes, the send headphone gets louder, if not it
is just a loud crosstalk keep searching.

BALANCED TESTING
                      Large Cable
       Selected wire ððððððððððððð Probe    Amp
               oÄÄÄ==ðððððððððððððÀ=========´>ÄÄÄÄo Detecting
Series Headphone) ³  ððððððððððððð  Screen ³ ³     )Headphone 
               o  ³                 lead   ÀÄÁÄÄÄÄo
 1kHz osc ÄÄÄÄÄÙ  ³
 floating ÄÄÄÄÄÄÄÄÙ

Here the cable is in audio pairs. When you hear the loudest tone in the
detecting headphone from the cable, short that pair of wires together, and if
the tone then goes, the send headphone gets louder, if not it is just a loud
crosstalk pair (fault?) keep searching.



Why don't you write an interesting bul?

73 De John, G8MNY @ GB7CIP


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