WARNING: DISCONNECT POWER PRIOR TO SERVICING
2-7
2-68.
TROUBLESHOOTING PROCEDURES.
The ECU assembly troubleshooting procedures are
presented in Tables 2-1 through 2-4. Table 2-1 presents the exciter circuit board
troubleshooting. Table 2-2 presents the stereo circuit board troubleshooting. Table 2-3
presents the controller circuit board troubleshooting. Table 2-4 presents the ECU power
supply troubleshooting. Refer to Tables 2-1 through 2-4 to isolate the problem to a
specific circuit. Once the trouble is isolated, refer to the circuit board theory of operation
and schematic diagrams to assist in problem resolution.
TABLE 2-1. EXCITER CIRCUIT BOARD TROUBLESHOOTING
(Sheet 1 of 3)
SYMPTOM
CIRCUITRY TO CHECK
LOCK INDICATOR
1. Refer to the factory test data sheets and ensure
EXTINGUISHED
the exciter circuit board frequency synthesizer
(S1, S2, and J6) is programmed for the correct
operating frequency.
2. Check U25 pin 1 for a 0V to 5V square-wave
signal at FcX4 (carrier frequency times four) or
FcX8 (carrier frequency times eight).
A. If the square-wave signal at U25 is not present,
check for a greater than 13 volt dc signal at the
anode of D23.
1. If the dc voltage is present, defective VCO, Q4,
or U30A.
2. If the dc voltage is not present, defective Q3
or C106.
B. If the square wave signal at U25 is below
FcX4 or FcX8, measure the dc voltage at J8
of the VCO assembly.
1. If the dc voltage at TP7 is greater than 13 volts,
defective VCO.
2. If the dc voltage at TP7 is less than 2 volts,
defective U25, U26A, U26B, Y1, or U24.
C. If the square wave signal at U25 is above FcX4 or
FcX8, measure the dc voltage at TP7 of the VCO
assembly.
1. If the dc voltage at TP7 is greater than 13 volts,
defective U25, U26B, U26A, Y1, or U24.
2. If the dc voltage at J8 is less than 2 volts,
defective VCO.
NO L+R MODULATION
1. Remove the stereo circuit board if present and
OF CARRIER DURING MONO-
place J4 in the left or right channel position
PHONIC OPERATION
as determined by the channel with applied audio.
2. Insert a +10 dBm 1 kHz signal in the appropriate
audio channel and check for audio at U39 pins 3
and 6.
A. If the audio is not present, defective: 1) left
channel - U39, U2A, U2B, U1A, or U1B 2)
right channel - U39, U4A, U4B, U5A, or U5B.
B. If the audio is present, defective U8A, U8B, U9A,
U9B, U14B, or U13.