Installation manual

GEM INSTALLATION MANUAL DOCUMENT No. 070906 REV. 1.3
INSIGHT
INSTRUMENT CORP. 19 BOX 122, FORT ERIE, ONTARIO, L2A 5M6
Symptom: No CHT in one or more columns.
Cause: Faulty probe. Turn top knob on GEM to the probe analysis page to check probe
Integrity. For 8 foot harness on probe analysis page resistance should be 8 - 3 EGT / 1 - 6
CHT. For 24 foot harness on probe analysis page resistance should be 26 - 10 EGT / 4 - 18
CHT.
Symptom: Display goes out during engine start.
Cause: Voltage transient or over voltage condition. The display should not be turned on during engine
start. An Avionics Master or separate power switch should be installed to apply power to the display.
Symptom: Display is unstable.
Cause: Noisy or defective magneto or ignition harness. Check operation on left and right
magnetos. The temperature should rise slowly and may stabilize slightly or completely on one or
the other magneto. Single magneto operation will pinpoint the problem to one ignition harness,
unless both are faulty. Verify that the probe wires and GEM series system harness are isolated
from the ignition harness. If necessary, repair or replace the faulty ignition harness to eliminate
ignition related interference.
Symptom: Display is unstable.
Cause: Magneto ungrounded or defective P-lead. Check ignition harness for proper shielding,
grounding, and loose spark plug caps. Check magnetos for proper grounding or evidence of arcing.
Disconnect magneto P-leads one at a time. If this eliminates or reduces the problem, replace the P-
lead. A faulty ignition harness will typically cause all EGT readings to “dance” up and down. The GEM
series Display will detect this type of fault long before standard test methods, thus eliminating the
potential of more serious problems.
Symptom: Display is unstable.
Cause: Noisy or defective alternator, defective generator or faulty ground connection. Try operation
with alternator or generator off. Alternator related interference may indicate faulty commutator.
Symptom: Display is affected by radio transmissions.
Cause: Proximity of probe and/or display unit to the radio power wiring and away from radios and
antenna coax. Check radio rack connector for missing 50 ohm matching device. The 50 ohm
matching device is a thick washer-like component part that is installed underneath the connector
end cap. The end cap will have to be unsoldered to check for the matching device. This seemingly
unimportant component is supplied with all connectors and is required for proper operation of the
connector. Utilize shielded-twisted pair for power leads.