Tektronix PHASER 380, Service Manual

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5-6
Phaser 380 Color Printer
5
Theory of Operation
Power supply
In general, the power supply has two main, yet interrelated sections: the AC
section and the DC section. In the AC section, AC power is routed to
opto-isolated triacs which, under main board logic control, supply AC power to
the twelve heaters in the printer.
Two fuses provide current protection to the triacs. Fuse F2 and F3 (both 10 A
slo-blo) protect the power supply from, most often, a shorted triac. If a F2 or F3
fuse blows, it is best to replace the power supply rather than the fuse.
Otherwise, with the fuse replaced, but the triac shorted, AC power may be
applied to the heater without the printer even being turned on. Each time the
main board turns on a triac to activate a heater, it is turned on for only a fraction
of a second. The main board must constantly readdress each heater it wants to
remain on. By this means, if the print engine firmware should fail, the heaters
automatically shut off. The printer is also protected by five thermal fuses
located inside these assemblies: the drum heater, the printhead’s two ink
reservoirs, the paper pre-heater and the cap/wipe/purge assembly. A thermal
fuse opens in the unlikely event of a ”runaway” heater following a firmware
failure. If a thermal fuse opens, its unit must be replaced.
The DC power supply gen5 volts for the printer’s logic, + 40 volts for the
motors, +54 volts and -54 volts for the printhead drivers, and +12 and -12 volts
for serial communication. The fuse F1 (6.3 A slo blo) provides protection for the
switching power supply in the DC section.
Warning The power-switch does not interrupt AC power to the power
supply, it only signals the supply and the printer logic to begin a
shutdown sequence. Even with the power switch in the OFF
position, AC line voltages are present on the power supply, heaters
and heater wiring. The power cord must be removed for
disassembly.
There are no field adjustments necessary on the power supply.