Troubleshooting the RADS-AT™

The following is a listing of common troubleshooting tips for the RADS-AT™. If you are unable to resolve a problem and require technical assistance, please contact Signal Processing Systems Customer Service at 1-800-826-2124 or contact one of our Aviation Systems Field Engineers.

1. CADU Unique Troubleshooting
   Most of the CADU unique errors can be attributed to damaged databases. This failure has two common causes. The first, a CADU overstuffed with data and script files and the second, a low lithium battery. The troubleshooting is similar for both problems. A reformat of the CADU will rebuild the directory structure and database to start clean.
   
   If the problem reoccurs within a short period of time (one to two weeks), the lithium battery is a likely suspect. The battery must be replaced. It cannot be charged. This is a procedure that can only be performed at an authorized repair facility.

2. DAU Unique Troubleshooting
   DAU failures are primarily found in the power-up self-calibration. When the DAU is turned on, it will wait for the CADU to give the current time and date to set its internal clocks. During this time, the DAU can be forced into a self test by an external terminal through a test cable. Once the CADU sends the DAU the date and time, the DAU will compare it with the most recent self-test. If it has been more than 24 hours since the last test, the DAU will perform a thorough test. Otherwise, it will perform the filter sweep only. If any one of these tests fail, the DAU will not allow a measurement to be taken. Approximately 90% of the DAU circuitry is tested in the self-test, including a sweep of the filters and redundant voltage, frequency and ground reference tests.

3. System Measurement Troubleshooting
   The most common types of failures during measurement are listed below, along with their most probable causes. This is not a complete list, but is meant to be more of a guide as to which direction to follow while isolating or replacing system components.

   3.1 DAU Not Ready or CADU Still Setting Up DAU

   a. A measurement was attempted too soon after the DAU was powered up. Normally it takes about 30 seconds for the DAU to self-test. However, if there are supplemental files in the CADU that need to be downloaded to the DAU (called overlay files), this communication can take up to two minutes.

   b. The DAU is hung up. This primarily occurs when the system is installed on an aircraft that starts from a battery rather than an Auxiliary Power Unit (APU). The DAU is turned on before the engines is powered up and the bus voltage drops when the engine is started. Occasionally the voltage will drop to a level which will lock up communication, but not low enough to cycle power on the DAU and start another reboot. The DAU needs to be shut off for a few seconds, then turned back on. The CADU then needs to be rebooted to start the process over again. This problem can also occur on APU-equipped aircraft in warm weather.

   c. The CADU-to-DAU cable is damaged. If the cable has been stressed (usually near the connectors), the wires can be damaged internally to the cable with no signs of external failure. The cable should be rung out and replaced if necessary.

   NOTE: If one of the wires happens to be a power wire, then the communications chips in the CADU and/or DAU may be damaged as well. Replacement of the cable may be too late.

   d. The tracker cable is damaged. The CADU senses the DAU by a requisite voltage level on the CADU-to-DAU cable. If the tracker cable is internally shorted on the power line, the short may be substantial enough to drag system power down to the point that the CADU does not recognize the DAU. Disconnect the UTD cable at the DAU, reboot both units and try the measurement again.

   e. Failure of the CADU or DAU processor board. These two boards communicate with each other through the CADU-to-DAU cable.

   3.2 Tachometer Out Of Bounds, Too High/Low Failure
   
   This is one of the most common types of errors. When working with the main rotor, usually the magnetic pick-up is used. Possible failures are:

   a. Magnetic pick-up cable failure. If the cable is not left with enough slack during installation, then the connector can be pulled off of the cable, when the collective is raised.

   b. Magnetic pick-up failure. Though durable they can fail. There are a couple of quick checks to verify the operation of a pick-up. There should be about 1 kOhm resistance between the two pins. If it reads more than 10 kOhm, then the pick-up is probably open or on its last leg. If an oscilloscope is handy, the operator can connect the oscilloscope across the two leads of the pick-up and wave a ferrous material (penknife or screwdriver) over the top. An operational pick-up will show a pulse.

   c. Gap too large or too small. If the gap is too large, the tachometer may fail. If it is too small, the striker plate may strike the magnetic pick-up causing it to ring, which will give a tachometer too high or tachometer out of bounds error.

   d. Corruption by other ferrous material. The use of wrong attachment screws on the swashplate.

   e. Optical pick-up cable failure. With power applied to the DAU, point the tachometer at the reflective tape. Is there a red light on the back of the sensor? Move to operational distance. Is there still a light?

   f. At installation, does the sensor see the tape? It works best off axis.

   g. Old tape still on the blade or other reflective material (blade label or other shiny surface).

   h. Tachometer on the wrong channel of the DAU.

   i. DAU internal failure. This could be due to noisy power supply or acquisition board.

   3.3 Track Signal Corrupted, Track Sensor Fault, Blades Apparently moving at the Wrong Speed, Blade Chords Different and Track First In/First Out (FIFO) Overrun

   a. Switch DAU to the night mode. This is the easiest first fix. It will disregard chord width errors and help with low light level conditions.

   b. Check the quality of the contrast. Do the leading edges of the blades need to be painted? Is there a possibility of InfraRed (IR) corruption (white concrete, white hangar, UTD looking into the sun,etc..)?

   c. Check that the UTD is installed properly. The arrow should be in the direction of the rotor rotation.

   d. Is the UTD cable damaged? Repeated door closings on the same spot will break the cable or cause too much tension at the UTD connector.

   e. Water intrusion in the UTD. Usually can be seen by looking down through the clear lens. If the UTD is prior to Revision K (found on the UTD ID plate), there is a possibility of water intrusion.

   f. Failure of the DAU processor board. DAU will have to be returned to the factory for repair.

   g. Corrupted CADU database. Reformat the CADU RAM amd reload the script files.

   A list of error codes can be found in the RADS-AT™ Operator's Manual.