System Maintenance Manual GTN 6XX/7XX Part 23 AML STC 190-01007-A1Page 4-6 Rev. 54.6 Transient Voltage Suppressor (TVS) (If Installed)After a suspected lightning strike, each TVS and TVS assembly (if installed) must be replaced. Refer toSection 6.8.1 for information on installing in-line TVSs.4.6.1 GTN TVS1 Check (GTN #1 Only)NOTEThe GTN should be the only LRU connected to the NAV/GPS circuit breaker. If otherequipment is connected to the NAV/GPS circuit breaker it must also be disconnected priorto conducting the following check. No other TVS devices should be on this circuit. If theTVS being checked is not isolated, erroneous readings may result.For a dual GTN installation, only GTN #1 will have the TVS protection. The following checks will onlyapply to GTN #1. Reference the appropriate GTN power interconnect drawings. To check the TVS on theGTN power inputs, the following steps should be followed:1. Remove the GTN as described in Section 6.1.2. Open the GTN’s circuit breaker and use a multi-meter to perform a diode check between P1001-19and ground:a) The meter should indicate open with the red lead on P1001-19 and the black lead on ground.b) The meter should indicate a diode drop of between 2.0V and 2.5V with the red lead onground and the black lead on P1001-19.i. If the diode drop is outside of the above range, replace the TVS.ii. If the meter indicates a short during steps 2a or 2b, replace the TVS.iii. If the meter indicates an open in both directions, check the continuity of the fuse.iv. If the fuse is open, replace the fuse and repeat the check.v. If the fuse is good, check the wiring for faults. If the wiring is good, replace the TVS.3. Verify continuity between P1001-19 and P1001-20.4. Reinstall the GTN as described in Section 6.1 and reset the GTN’s circuit breaker.
