Power Supply - Printronix P6000 Series Maintenance Manual

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2-9. Power Supply

c. +36 V Supply, P6080 Only (Figure 2-22)
A full wave rectifier consisting of half of the +70 Volt bridge and two SCRs rectifies the voltage
from the +36 V winding. Each SCR controls the duration of current flow during one half cycle. A
feedback circuit maintains a relatively constant pulsating dc voltage at the SCR cathodes.
The pulsating dc voltage passes through a choke on the power supply chassis to filter R1/C1. Fil
tered +36 Vdc powers the hammer bank and the hammer driver PCBA. Filtered +36 Vdc is fused,
regulated, and connected to the circuit breaker to trip the circuit breaker when the +36 Vdc volt
age becomes excessive. Regulated +36 Vdc is also connected to a switching circuit that produces
switched +36 Vdc voltage, VSW, for the ribbon drive assembly.
The comparator amplifier samples the regulated voltage and compares it with the 1.0 Volt VREF
level. The SCR in the optical coupler ensures that the rectifier SCRs are turned off only at the zero
crossover of the ac waveform.
d. +70 V Supply, P6080 Only (Figure 2-22)
The +70 Vdc supply powers the paper feed drive circuits. The supply is derived from the 36 Vac. A
rectifier produces a pulsating +70 Vdc which is filtered.
e. Reference Voltage Circuit, P6080 Only (Figure 2-23)
Filtered +9.5 Vdc from the transformer secondary is attached to the reference voltage circuit and
used as a positive voltage reference source (+9.5 V) for the fault detection circuitry. The +9.5 V is
fused and applied to the +2.6 V regulator. The +2.6 V regulator provides the bias for the +5 V
regulator and is the input to the 1.0 V VREF amplifier. The reference level is precisely set by fac
tory selected resistor.
f. +5 V Supply, P6080 Only (Figure 2-24)
The regulated +5 Vdc supply provides power to all TTL circuits in the printer. It also generates the
hammer bank master clear signal, HMC, at initial power-on to prevent spurious hammer release.
g. Fault Detection, P6080 Only
Four fault sources are monitored: +5 Vdc, -36 Vdc, +9 Vdc, and the paper out switch. Any time a
voltage supply is out of tolerance or the paper out switch is actuated, the corresponding LED is lit.
h. Paper Feed Disable, P6080 Only
The paper feed disable circuits are controlled by the paper drive enable signal, NPDE. When
NPDE is active, the paper feed disable signal NPFD is inactive and the paper feed pair signal,
PF1/PF2, reach the paper feed drivers. The VSW logic switch is enabled, and VSW powers the
ribbon assembly thereby activating the ribbon transport. When NDPE is inactive, NPFD becomes
active, PF1/PF2 are kept from the paper feed driver and VSW is switched off, halting the ribbon
transport.
2-9. Power Supply
i. MOS Supplies, P6080 Only (Figure 2-23)
There are MOS circuit elements that require +12 Vdc and/or -12 Vdc. These two voltages are
supplied by simple zener regulators on the PCBA. +12 Vdc is derived from the +36 Vdc supply,
while -12 Vdc is derived from the -36 Vdc supply.
P6040/P6080 Principles of Operation
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