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Troubleshooting Bus

Troubleshooting the Ockam Bus

The Ockam bus supplies power from the CPU to all indicators and interfaces. The bus also carries signals in both directions between the CPU and the indicators and interfaces. In effect, all the boxes of the system are connected together by the bus cable and connectors.

Bus voltageTroubleshooting the bus is easier with a voltmeter. The bus carries DC power, and measuring it makes it faster to determine if the bus is OK.

There are three general types of problems that can happen:

Open Bus – Some parts of the system are off

An open bus causes some parts of the system to be disconnected from the other parts. Those components downstream of the open from the processor will be deprived of both power and signals. If they are indicators, it is evident which ones they are, and therefore approximately where the open may be.

If only interfaces are downstream of the open, the only way you might notice is if some of your functions stop changing. See Configuration to determine which interfaces might be disconnected.

Starting at a dead bus location, measure the voltage at the connector. If it is dead, move to the next connector toward the processor.

Most opens occur at the connectors at either end of the cable. Inspect the connector and the cable for frayed wire or evidence of corrosion. A properly installed connector can withstand 2 lb. of pull. If you suspect a connector, try pulling on it.

Vibration can also cause the center conductor to break due to fatigue. If you have a bad cable, you can use an ohm meter to check the continuity between the center contacts and shells of the connectors at both ends.

Tee connectors can fail if they get wet due to plating action from the supply voltage. Salt water is more of a problem than fresh water. Look for corrosion on or inside the connectors.

Shorted Bus – All the components are off except the processor

A shorted bus shorts out the bus power supply, removing power and signals from all indicators and interfaces. All indicators will be blank, but the processor has power. The short can be in a cable, a tee connector or one of the boxes of the system.

To find a short, disconnect the bus at processor. Confirm that 9 volts are present on the processor connector. If no voltage is present at the processor, it should be returned for service.

Reconnect each cable and component in turn, checking the far end of each cable for voltage. Continue this process until you isolate the problem to a single element.

If the problem is in a cable, inspect the two connectors and the cable itself for a crushed area. If the problem is a tee, it will have to be replaced. If the problem is in one of the boxes, it should be returned for service.

Intermittent bus

Intermittents can be either opens or shorts (see above), but can also produce false signals if the shorts or opens are of short duration, or the short is not complete. If the symptoms are the same as open or shorted, diagnose them as described above.

Intermittents which produce false signals give occasional TEST Error code 13, create displays with odd characters or cause outputs to react strangely. These symptoms are usually the result of arcing or conduction through water that has gotten into the Ockam Bus cables and connectors. It indicates that the Ockam bus needs overhauling. You should inspect all cables and replace any that are wet, have corrosion or frayed wires or get warm.

 

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