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POWER SUPPLY TROUBLESHOOTING GUIDE
It is highly recommended that a variable isolation
transformer which can monitor current be used.
(Alternatively a variable AC source which monitors
current will do). Read directions below before
power is added!
CHECK
Check Fuse (F601) is blown out
or not.
If fuse is blown out,
do repair method #1.
NO
Check whether the primary
rectifying DC of the Switching
power supply has an output.
(Reading should be about 168V.)
YES
Voltage of the 105V line higher
than normal?
NO
The transformer of the power
supply makes a higher sound or
the oscillation wave form is
abnormal.
(E.g. intermittent oscillation)
Connect the positive probe of
oscilloscope to the pin 16 of
T601, then connect the negative
probe to the pin 12. Observe the
waveform and check to see if the
waveform is out of limit of value
shown in Fig. 1.
NO
There is no problem on the SW
power supply.
Voltage approx. 5 Vp-p
0 V
T = Approx. 6 to 14 µsec.
Oscilloscope setting: 1 V/DIV.
Repair method #1
(Power must be off)
Short circuit in the secondary side. check diode D613,
D614, D616, D617 and D618, switching transistor
(Q601), control transistor (Q602), diode and resistor
Repair
replace as necessary.
method
Disconnect 105V diode (D613), 25V diode (D614), 8V
diode (D616), 12V diode (D617), 12V diode (D618)
and Check the load continuity of 105V line, 25V line,
YES
#1
8V line, 12V line through a tester (resistance range).
If the tester indicates a lower resistance value around
0 ohm, the line is short-circuited.
Before repairing the switching power supply, find out
NO
the short-circuited area of such line and repair it.
#2
If the tester does not indicate any low resistance value
(around 0 ohm), no load is short-circuited and there is
no problem.
YES
#3
Check for any defective parts while the secondary
rectifying diodes are disconnected (D613, D614,
D616, D617 and D618) perform a diode check in both
forward and reverse directions through a tester.
Repair method #2
Check the primary rectifying diodes (D603-D606) as
YES
possible problems. Remove the above mentioned
#4
parts and check them. Perform check according to the
step 1 and 2 of repair method #1 and check for defects
following parts, then if necessary replace with factory
originals.
R602 is open or not.
Q601, Q602, D607, D608 and D611 are short or not.
Repair method #3
The feedback circuit which is monitored by the output
of D613 105V may not work and this may be regarded
as a possible cause, remove IC601 (Photo Coupler),
diode (D620) and transistor (Q604) check for defects.
Repair method #4
Check control circuitly which is connecting to Pin 2
and 1 of Switching Transformer T601.
2 µsec./DIV
Fig. 1
1-9-1
T5517TR
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