A Video Graphics Array, or VGA, cable links the video output from a computer or laptop to the monitor. A VGA cable has other uses in gaming machines and other electronic equipment. VGA cables terminate with 15, 14 or nine-pin connectors, depending on the type of connector used. Depending on the intended use, some of the pins may be absent. When a cable fails, perform a continuity test on each individual wire.
Select the continuity option on a digital multimeter, often marked with a "sound wave" symbol. Touch the meter probe tips together. The meter display should read zero ohms, indicating that the circuit is complete. Most meters "bleep" when continuity is confirmed.
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Touch one meter probe to the top left pin of one of the connectors. Hold the probe in place while touching the other probe to the identical pin on the other connector. The meter will read zerp if the wire between the two pins is in working order. A reading of "1" or "OL" indicates a broken wire.
Work along the rows of pins, connecting the probes to each pair of pins in turn. Note the positions of pins that fail the continuity test. Compare your results to a pinout diagram for your cable; some pins may intentionally be disconnected.
Check the pinout diagram to discover which color wire is connected to each pin. If the connector can be taken apart, open it and look. Sometimes this will be the only way to work out which wire connects to which pin.
Cut away a 1/2 inch of the cable insulation at the center of the cable. Remove the outer insulation but don't damage the wires inside. If the cable is wrapped in foil or paper, part it to access to the individual wires. Locate the specific wire that failed the test.
Push a needle gently into the suspect wire. Pierce the insulation, but don't push right through to the other side. Connect one meter probe to the needle and the other to the appropriate pin on one of the connectors. Check the continuity. Move the second probe to the other connector and repeat the test. The cable fault lies in the half of the wire that failed the test.
Keep one probe attached to the connector at the broken end of the cable. Progressively move the needle closer to the connector, inserting it and checking the meter each time. When the cable passes the test, the fault lies between that point and the previous test point. Pinpoint the location by performing more tests between the two points.
Cut away the insulation surrounding the break in the cable. Strip 1/8 inch of insulation from each end of the broken wire to leave two short sections of exposed metal.
Twist the two exposed ends together between your fingers, binding them tightly. Conduct a continuity check along the entire length of the repaired wire to confirm that the break is repaired.
Repeat for each damaged wire within the cable. When finished, complete the repair by wrapping electrical insulating tape around all the areas where the insulation was removed.
Things You'll Need
Needle or pin
Before assuming that a cable is at fault, try a different cable that is known to work. If the symptoms persist, then the fault may lie elsewhere. The most common VGA connector has 15 pins, mini-VGA connectors have 14 pins and the old and largely obsolete version has nine pins. The connector pins on a 15-pin connector are identified as:
Top row: 1 to 5 Middle row: 6 to 10 Bottom row: 11 to 15
Repairs to a VGA cable may lead to reduced signal quality.