Service manual

EPSON Stylus Photo 870/1270 Revision B
TROUBLESHOOTING Overview 68
9 Is the switching FET
(Q1) defective?
Check the electrical continuity of the switching
FET by trying the four patterns below. If the
main switching FET is good, the results should
be as shown under the figure.
NOTE:
Be sure to pay attention to the polarity.
10 Is an NPN junction
transistor defective?
Check the electrical continuity of an NPN
junction transistor on the power supply board.
NOTE:
Be sure to pay attention to the polarity.
Table 3-10. Isolating the Faulty Part on the Power Supply Board
Step Checkpoint Action
G
D
S
+
-
G
D
S
+
-
G
D
+
-
G
D
+
-
tr18
Step 1: Off
Step 2: On
Step 3: Off Step 4: Off
+
+
+
+
-
B
E
C
NPN Tr
B
C
E
B
C
E
B
C
E
B
C
E
-
-
-
tr19
Step 1: On Step 2: Off
Step 3: Off
Step 4: On
11 Is a PNP junction
transistor defective?
Check the electrical continuity of a PNP junction
transistor on the power supply board in the
same manner described in the previous step.
NOTE:
Be sure to pay attention to the polarity.
12 Is the regulator IC
(IC51) defective?
Using an oscilloscope, check the output
waveform at Pin 8 of IC51. The output
waveform should be as shown below:
Table 3-10. Isolating the Faulty Part on the Power Supply Board
Step Checkpoint Action
+
+
+
+
-
B
C
E
B
C
E
B
C
E
B
C
E
-
-
-
tr20
B
E
C
PNP Tr
Step 1: Off
Step 2: On
Step 3: Off
Step 4: On
To Pin 8
(Output)
To GND
IC51
Output Waveform