Garmin G300 Installation Manual page 90

1. Inspect GSU73 pitot/static plumbing integrity
2. Inspect pitot/static ports and associated equipment
3. If the problem persists replace the GSU 73 with a known good unit
10.4.1 Troubleshooting GSU 73 Engine Indication Failures
See Figure 10-5 for example. The following may help to determine to cause of an Engine Indication
failure.
1. Does cycling power restore operation?
2. Did the operator give it sufficient time to start and initialize?
3. Did the problem begin after a software or configuration load?
4. Did the problem happen on the ground or while airborne?
5. Is only the EGT Red-X'd? If so, the GSU 73 configuration module, configuration module
wiring, thermocouple reference, or applicable thermocouple is defective. Check the wiring
and replace the configuration module or applicable thermocouple.
6. Are there one or more temperatures that drop as the electrical load increases? If a
temperature probe shorts (usually where the bayonet is crimped) a ground loop is created
forcing the reference (lo side) to increase which causes the temperature reading to decrease.
7. Does the EGT temperature slowly drift up and eventually flag? This is an indication of an
(electrical) open in the temperature probe or wiring.
8. Is the air data information on the PFD intermittently Red-X'ing? If the GSU 73 +5VDC
transducer power supply is shorted to ground, it will cause an intermittent air data Red-X
issue to occur.
9. If the AMP indication Red-X'd, check the Alternator Shunt for correct resistance. Refer to
the Cessna Aircraft Manual.
10. If the Trim Indication is Red-X'd. check the Elevator Trim Pot Sensor and wiring.
Page 10-8
Revision A
G300 Installation Manual –Troubleshooting
190-00921-01