5-16
DECcolorwriter 1000
5
Theory of Operation
Fusing is provided by two in-line fuses on the AC input line. Overvoltage protection for
the +25.5 VDC and +5 VDC supplied is provided by a “crowbar” circuit formed by a
Zener diode and an SCR. +25.5 VDC overcurrent is sensed and regulated by altering the
oscillations of the pulse-width-modulator that generates the voltage. Overheating is
detected by a thermostat that also shuts down the pulse-width-modulator oscillator.
Figure 5-10. Power supply block diagram
L
SW1
F1
F2
N
FG
Input filter
Rush
current
preventing
circuit
Rectifying/
smoothing
double-voltage
circuit
SW2
115 V/230 V selection SW
T1
Overvoltage
protecting
circuit
T2
T3
VR1
VR2
25 V output
SW circuit
Overheat
protecting
circuit
Control circuit
5 V output
chopper circuit
Control circuit
12 V
-12 V
GND
25 V
VH
VHON
5 V
GND
F3
F4
25 V
rectifying/
smoothing
circuit
±12 V
rectifying/
smoothing
circuit
±12 V output
SW circuit
8699-61A
.
.
.
.
.
.
.
.
Summary of Contents for DECcolorwriter 1000
Page 11: ...Service Manual xi...
Page 16: ...Service Manual xv...
Page 56: ...2 24 DECcolorwriter 1000 2 Installing the Printer and Drivers...
Page 64: ...3 8 DECcolorwriter 1000 3 Verifying the Printer and Host Connections...
Page 70: ...4 6 DECcolorwriter 1000 4 Key Operator Training...
Page 170: ...8 46 DECcolorwriter 1000 8 FRU Disassembly Assembly...
Page 190: ...9 20 DECcolorwriter 1000 9 Checks and Adjustments...
Page 195: ...Service Manual A 5 Field Replaceable Units List A...
Page 198: ...A 8 DECcolorwriter 1000 A Field Replaceable Units List...
Page 204: ...C 6 DECcolorwriter 1000 C Wiring Diagrams...
Page 208: ...D 4 DECcolorwriter 1000 D Test Pattern Generator...