photo Technician's Bench
Yaw Damper Quick Bench Test

by Butch Nimmo, Tech Rep

Many S-TEC dealers don't have sufficient yaw damper sales activity to justify the purchase of our yaw damper bench test set. The ability to perform a quick bench test can be a valuable troubleshooting tool during initial installation of a yaw damper system, or whenever a yaw damper system is suspected of a malfunction.

The following procedure and parts list gives you the capability to perform a quick bench test of the yaw damper amplifier, with minimal investment.

Items you will need include an S-TEC PN 9524 breakout box, 0-28 VDC power supply, DVM, 30°/60°/90° triangle, 5 K potentiometer, assorted pin plugs, 22 gauge wire, and a 25 pin to 50 pin adapter cable. The 5K potentiometer, as well as all of the component parts necessary to fabricate the adapter cable, are available from S-TEC. You may contact our sales department to purchase these parts.

Fabricate the adapter cable using all 25 positions of the 25-pin receptacle. Connect each pin of the 25-pin receptacle to the same pin position in the 50-pin receptacle (i.e. 1 to 1 thru 25 to 25). 

YAW DAMPER QUICK BENCH TEST PARTS LIST

P/N           DESCRIPTION         QTY 
3411          50 Pin "D" Recpt.     1
3423          25 Pin "D" Recpt.     1
5208          "D" Crimp Socket     50
5504          50 Pin Cover          1
5519          25 Pin Cover          1
6127          25 Pin  Lock Lever    1
37082209      22 Ga. Wire         A/R
2115023001-1  5K Potentiometer      1
A quick bench test of the yaw damper amplifier can be performed using the following procedure:

1. Connect the 50 pin plug on the 9524 breakout box to the 50-pin receptacle of the Adapter cable.
2. Connect the 25-pin receptacle of the adapter cable to the yaw damper amplifier.
3. Solder 18" 22 GA wires to each of the terminals of the 5 K potentiometer and cover solder connection with shrink tubing. Terminate each wire with a pin plug.
4. Connect the 5K potentiometer to the breakout box per Figure 1.
5. Connect a jumper, pin 24 to 20.
6. Connect the DVM (+) to pin 11.
7. Connect the DVM (-) to pin 5.
8. Apply the proper voltage (14/28) to pin 4 and ground to pin 19.
9. Hold the yaw amplifier so that it is in a vertical position with the "up arrow" at12 o'clock (0°).
10. The DVM should read 0.0± .30 VDC. If it does not, no further testing is required. The unit should be returned to S-TEC for repair.
11. Move the DVM (+) lead to pin 1. Move the DVM (-) lead to pin 2. Adjust the 5K potentiometer for 0± .10 VDC.
12. Tilt the yaw damper amplifier 30° clockwise using the triangle for reference. The DVM should read one of the following voltages depending on which P/N is being tested: 

	
    P/N                     Voltage
    0121, 0121-2, 0121-4    -4.0± .50 VDC (14V units)
                            -8.0± 1.0 VDC (28V units) 
    0121-1                  -5.5±  .60 VDC (14V units)
                            -11.0± 1.20 VDC (28V units)
13. Tilt the Yaw Damper amplifier 30° counter clock wise using the triangle for reference. The DVM should read one of the following: 
                      
    P/N                     Voltage
    0121, 0121-2, 0121-4    +4.0±. 50 VDC  (14V units)
                            +8.0± 1.0 VDC (28V units)        
    0121-1                  +5.5± 60 VDC (14V units)
                            +11.0± 1.20 VDC (28V units)
14. Remove the jumper from pin 24 and pin 20. The DVM should indicate a pulsing DC voltage.
15. Return the yaw damper amplifier to the vertical (0°) position.
16. Move the DVM (+) lead to pin 3. Move the DVM (-) lead to pin 6.
17. Apply the proper voltage (14/28) to pin 13. The DVM should read: 
    13+ 1.0 VDC (14V units)
    27± 1.0 VDC (28V units)
This simple test allows for quick verification of proper yaw damper amplifier basic operation. Keep the 25 to 50 pin adapter cables handy. We will use it again in an upcoming issue of the approach when we perform a quick bench test of the ST-360 altitude selector/alerter.

Figure 1

Figure 1 
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