Cessna 177 SERIES Service Manual page 277

16-50. TROUBLE SHOOTING (Cont).
TROUBLE
PROBABLE CAUSE REMEDY
INSTRUMENT LIGHTS WILL Defective wiring.
2. Test circuit until short is lo-
NOT LIGHT (THRU 1974
cated. Repair or replace wiring.
MODELS). (Cont.)
3.
Test for open circuit. Repair
or replace wiring. If no short or
open circuit is found, proceed to
step 4.
Defective rheostat.
4. Check voltage at instrument
light with master switch on.
Should read battery voltage with
rheostat turned full clockwise
and voltage should decrease as
rheostat is turned counterclockwise.
If no voltage is present or voltage
has a sudden drop before rheostat
has been turned full counterclock-
wise, replace rheostat.
Lamp burned out.
5. Test lamp with ohmmeter or
new lamp. Replace lamp.
INSTRUMENT LIGHTS WILL Short circuit wiring.
1. Inspect circuit breaker. If
NOT LIGHT (1975 MODELS circuit breaker is open, proceed
& ON). to step 2. If circuit breaker is
OK, proceed to step 3.
Defective wiring.
2. Test circuit until short is lo-
cated.
Repair or replace wiring.
3. Test for open circuit. Repair
or replace wiring. If no short or
open circuit is found, proceed to
step 4.
Faulty section in dimming 4. Lights will work when control
potentiometer.
is placed in brighter position.
Replace potentiometer.
Faulty light dimming 5.
Test both transistors with
transistor. new transistor. Replace faulty
transistor.
Faulty selector switch.
6. Inspect. Replace switch.
INSTRUMENT LIGHTS WILL Open resistor or wiring in 1. Test for continuity. Replace
NOT DIM (1975 MODELS & ON). minimum intensity end of resistor or repair wiring.
potentiometer.
Shorted transistor. 2. Test transistor by substitution.
Replace defective transistor.
Change 6 16-17