Epson DFX-8000 Service Manual page 173

REV.-A
5.3 POWER SUPPLY BOARD UNIT COMPONENT REPAIR
This section describes the power supply circuit operation check and component repair of the
BOPS/BOPSE board. Before starts the troubleshooting of the other units, you should be check the
operation of power supply unit.
Table 5-3 shows the troubleshooting procedures for the power supply board unit
Problem
Symptom
Voltage is
(fuse) is
not output blown right
correctly. after
replacement.
None of the
output volt-
ages are
normal.
not normal.
Table 5-3. Power Supply Board Unit Component Repair
Cause
The line filter
circuit ele-
The rectifier
circuit ele-
DB 1 (diode
bridge) is
bad.
The surge
cut circuit is
bad.
switching
transistors
are bad.
The rectifier
diode DT1 is
bad.
Checkpoint
Check if any of C 1 – C7 or R 1 is
shorting the AC line.
Check if DB 1 has shorted or if any
of the elements connected be-
tween the positive and negative
terminals of DB 1, C9, C 10, Q 1,
. When DB 1 shorts, it may be be-
cause a short has occurred in a
latter stage of DB 1.
Verify that approximately 300V of
DC voltage is output between the
positive terminal (pin 3) and the
negative terminal (pin 4) of DB 1.
The output voltage of DB 1 may
be constrained due to a prob-
lem with an element in DB 1's
latter stage.
Measure the AC voltage between
DB 1 pin 2 and L2 pin 4, and verify
that it is approximately OV.
Either TY 1 is bad, or any of the
components (R4, C8, D 1, or T 1 )
that switch TY1 are bad.
Observe the drive waveforms of
the switching transistors at IC 1 pin
8 and pin 11. (See Figure 5-1 1.)
The drive waveforms of pins 8
and 11 have a phase difference,
but the signal levels are the
same.
When DTC (pin 4) is at 100'Yo
(more than 3.5 V), the drive
waveforms are not output.
Observe the waveforms at the pri-
mary side (9 to 11 ) of transformer
Tl, and verify that Q1 and Q2 are
switching. (See Figure 5-1 2.)
Verify that the DC voltage (approxi-
. If no DC voltage is output,
check the secondary (output) of
T1.
5 - 1 2
Solution
Replace the abnor-
mal element(s).
Replace DB 1 and the
abnormal element(s).
Replace DB1 and the
abnormal element(s).
Replace TY 1 and the
abnormal element(s).
Replace IC 1.
Replace Q1 and Q2,
or the surrounding el-
(including
Replace DT1 or the
surrounding
element(s).