Service manual

Operating Principles
EPSON FX-880/FX-1180 Service Manual
2-13
To protect the printer, the power supply board incorporates over-voltage and over-current protection
circuitry. If the 5 V supply exceeds +7 VDC, or if the 35 V supply exceeds +36 VDC, the operation of the
ZC-RCC switching circuit is immediately stopped, and its output falls to zero. In addition, a voltage drop
protection circuit protects the printer in case of a short circuit in any component that draws from the +35
VDC line. If a voltage drop is detected, this also stops the operation of the ZC-RCC. Fuse F1 protects the
power supply itself.
Normally, the printer is turned on and off using the Operate switch on the front control panel. When the
printer is turned off, the switching circuit is de-energized and output at +35 VDC stops. However, since
the Operate switch is in the secondary circuitry, current continues to flow in the primary circuitry as long as
the printer remains plugged in. Therefore, you should unplug the printer from the external AC power
source before performing maintenance.
The following figure shows the power supply circuitry in block diagram form.
Figure 15. Power Supply Circuit Block Diagram
Figure 16. Power Supply Board Component Layout (C229 PSB/PSE/PSH)
AC input Line Filter
ZC-RCC Switching
Rl
Overcurrent
i
Overvoltage
i
Regulator
IC
+5VDC
+35 VDC
Regulator IC
PSC
Transform er
R e g u la to r IC
CN1
CN2
Switching FET
Fuse
D iode Bridge
Photo-coupler