Tektronix PHASER 380, Service Manual

Page: 149 / 346

Service Manual 6-9
Troubleshooting
6
Testing for a shorted DC load
The power supply may shut down because of a shorted load.
1. Turn the printer off.
2.
Disconnect the DC power cables: J13, J14, J15, J16, J18, J19, J20, J22 and
J24, from the power control board. Turn the printer on (this isolates
all motors). If the rear fan turns and the rear panel LEDs illuminate,
proceed to the next step “Testing motor and solenoid resistances” on
page 6-10. It is probable that a failed driver on the power control
board has failed. Checking the motors and solenoids reduces the
change that a driver will be damaged by a defective motor.
3. Disconnect the two I
2
C bus cables J108, and J206 from the power
control board (this isolates all I/O boards and solenoids). Turn the
printer on. If the rear fan turns and the Status LEDs illuminate, isolate
which I/O board is shorting.
4. Replace the main board. Refer to the topic, “Main board” on
page 8-68.
5. Replace the power supply. Refer to the topic, “Power supply” on
page 8-62.
Note The power supply must have a minimum load to operate. The main
board provides this loading with large ballast resistors.
6. Replace the power control board. Refer to the topic “Power control
board” on page 8-69.