Epson Stylus PHOTO 1270 Service Manual page 68

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