Epson LQ-1500 Service Manual
LQ-1500
SERVICE MANUAL
Printed on Recycled Paper
a9
®
EPSON
1.1 Product Overview
1.2 LQ-1500 Interface Overview
1 .3Specifications
1 .4Major Components
2.1
General..
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2.2 ConnectIon Diagram
2.3 Connector Pin Assignment
Connector on UXMCL circuit board..
2.3.1
Connector on UXDRV circuit board..
2.3.2
Connector on UXPS/PSU 24E circuit board..
2.3.3
2.4
Electrical Circuit
Power circuit
2.4.1
2.4.2 Reset circuit
Sensor circuit..
2.4.3
Carriage motor control circuit..
2.4.4
LF motor control circuit
2.4.5
2.4.6 Head driver circuit
Auto sheet load circuit
2.4.7
Other function..
2.4.8
2.5 Printer Mechanism..
Operation
2.5.1
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TABLE OF CONTENTS
CHAPTER 1
GENERAL
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CHAPTER 2
PRINCIPLES OF OPERATION
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1-1
1-1
1-1
1-4
2-1
2-1
2-3
2-3
2-8
2-12
.......... 2-13
2-22
2-22
......
2-26
2-34
2-37
2-39
2-40
2-41
2-41
CHAPTER 3
OPTIONAL EQUIPMENT
3.1 Centronics Compatible Parallel Interface
Introduction
3.1 .1
Specification.. ................................ ..............................
3.1 .2
Operating principal
3.1 .3
Block diagram..
3.1.4
Circuit diagram
3.1 .5
Component layout ...............
3.1 .6
3.2 RS-232C/Current Loop Interface..
lntroductron ............
3.2.1
Specification.. ........
3.2.2
Operating principal ....................................... ....................................................
3.2.3
Block diagram....................................... ..... .............................................................................
3.2.4
Circuit diagram.. ......................... .......... .....
3.2.5
Component layout ....................................................................................................................
3.2.6
3.3 IEEE-488 Interface..
Introduction .......... ........ .............................................................
3.3.1
Specification.. ..... .........
3.3.2
IEEE-488 operatronal parameters.............................
3.3.3
IEEE-488 functional commands .........................................
3.3.4
Block diagram..... .............................. .................
3.3.5
Circuit diagram.. ................................... .......
3 3.6
Component layout ................................
3.3.7
3.4 Single Bin Cut Sheet Feeder (# 8334), Double Bin Cut Sheet Feeder (# 8344)
Introduction ......... ...........................
3.4.1
Specifications.. ..... ........ .......... ...... .................................................
3.4.2
Principle of operation.. ........... ...................................................................
3.4.3
Disassembly and assembly..
3.4.4
Troubleshooting.. .........................................
3.4.5
Preventive maintenance ...... .........................................................................................
3.4.6
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3-1
3-1
3-4
3-6
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3-7
3-9
3-9
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3-9
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3-15
3-19
3-21
3-22
3-22
3-31
3-33
3-33
3-34
3-52
3-60
CHAPTER 4
DISASSEMBLY/ASSEMBLY AND ADJUSTMENT
4.1
General..
4.2 Tools and Measuring Instruments
4.3 Disassembly and Assembly..
4.3.1 Removal of upper case
4.3.2 Removing the circuit boards..
4.3.3 Removal of Model-3660 printer mechanism..
4.3.4 Removal of fan set UB (head cooling fan).
4.3.5 Removal, installation and adjustmnent
4.3.6 Removal of CPU and ROM.
4.3.7 Adjustment of print alignment (backlash)
4.4 Adjustment.........................
4.4.1 MTS and DTS sensor board adjustment..
4.4.2 H.P. sensor board adjustment
4.4.3 Backlash of the carnage motor and belt driving pulley..
4.4.4 Backlash of the paper feed motor and
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........................... 4-6
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of print head..
paper feeding reduction gear
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CHAPTER 5
TROUBLESHOOTING
5.1 Entry of Troubleshooting
5.2 Check-out Procedure
5.3 Unit Repair Flow Chart (UXMCL).
5.4 Unit Repair Flow Chart (UXDRV)
5.5 Unit Repair Flow Chart (UXPS).
5.6 Unit Repair Flow Chart (IUPIF)
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4-1
4-2
4-2
4-3
4-6
4-7
4-10
4-12
4-12
4-1 4
4-15
4-16
5-1
5-4
5-18
5-33
5-40
5-42
CHAPTER 6
MAINTENANCE
6.1
Maintenance
6.1 .1
Cleaning..
6.1 .2 Inspection..
6.2 Lubrication..
6.2.1 Lubricants..
6.2.2 Lubrication requirement
6.2.3 Lubrication
6.2.4 Adhesive application requirements
6.2.5 Adhesive application points..
6.2.6 Lubricants and adhesives list..
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point.. .....................................................................................................................
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CHAPTER 7
APPENDIX
List of principal IC’s..
Description of principal IC's
Exploded diagram for LQ-1500..
Lubrication and adhesive application points drawing A
Lubrication and adhesive application points drawing B.. ............................................................................
Lubrication and adhesive application points drawing C
UXMCL circuit diagram
Component layout of UXMCL board.
UXDRV circuit diagram..
Component layout of UXDRV board..
UXPS circuit diagram..
Component layout of UXPS board..
PSU 24E circuit diagram..
Component layout of PSU
UXFIL circuit diagram ..................... ..........................................................................................................
II
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24E board ........................................................................................................
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6-1
6-1
6-2
6-2
6-2
6-2
6-3
6-3
6-4
7-1
7-2
7-35
7-36
7-37
7-38
7-39
7-40
7-41
7-42
7-43
7-44
7-45
7-46
7-47
INTRODUCTION
This technical manual describes the principle of mechanical and electrical
operations, as well as the maintenance and repair procedures, of the EPSON
LO-1500 Dot Matrix Printer.
Chapters 4 through 6 of the manual deal with the fundamental troubleshooting, maintenance and repair of the LO-1500.
For detail on the disassembly, assembly, troubleshooting and maintenance of
the Model-3660 Printer Mechanism, refer to the separately published “Technical Manual of EPSON Model-3660”.
* The contents of this manual are subject to change without notice
Ill
CHAPTER 1
GENERAL
1 .1
Product Overview..
1.2 LQ-1500 Interface Overview
1.3 General Specifications
1 .4
Major Components..
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1-1
1-1
1-1
1-4
1 .1 Product Overview
The LO-1500 is a serial terminal printer, featuring 200 CPS, bi-directional printing (draft pica mode) with
logical seeking capability, and 24 x 24 dot-matrix character formation.
which permit connection of the printer to various computers are optional.
cartridge type, which can be set snugly into the housing.
Should maintenance or repair be required, the printer mechanism and circuit boards of the LQ-1500 are
readily replaceable. The technician can perform maintenance and repair quite easily by referring to this
manual.
All interfaces for the LO-1500
The interface circuit boards are
1.2 LQ-1500 Interface Overview
(1) Centronics-compatible, parallel interface
This standard communication link permits data exchange with many computers without modification
or addition of other peripheral devices.
(2) RS-232C/Current Loop Serial Interface
A 20 mA current loop type, serial interface which permits the printer to receive data at a bit rate
ranging from 75 to 19200 BPS.
(3) IEEE-488 Interface
An optional interface which permits parallel communication between the printer and any computer or
measuring
488-l975.
instrument which is equipped with bus structure conforming the IEEE-488 Std.
1.3 General Specifications
(1 )
Printing Method . . . . . . . . . . . . . . . . . . . . . . . .._......
(2)
Character . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(3) Character Structure
Character
Draft
LO
ProportIonal
(4) Character Size SeeTable1. on the page 1-3
(5) Column Width..
(6)
Print Speed
(7) Paper Feed
(8) Paper
@
Cut sheet
Paper width ..,,._..........................
Paper thickness .
Weighing .._.............. .
................................ See Table 1. on the page 1 - 3.
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Impact dot matrix
1.
Draft
2. Near letter quality (LO)
3. Proportional (standard)
4. Multi-font (with option card)
5. Super/subscript in each above character style. (1 to 4.)
Normal
9x17
font
15 x 17
37x17
See Table 1. on the page 1 - 3.
Friction feed (standard)
Adjustable tractor feed (option)
182 mm to 364 mm
0.06 mm to 0.1 mm
45 kg to 70 kg (52 to 82 g/m*)
font
font
Super/Subscript
7
x
11
font
11
x
11
font
23 x
1 1
font
1-1
@
Fanfold paper
101
paper width
Copies
Paper thickness and Weight
Notes:
1. Jointing finish of copies should be point or line pasting.
2. Release the friction feed during the tractor feed operation.
3. Set the head adjusting lever as shown in above table.
However, adjust the step setting within range +1 step, depending on print density.
mm to 406 mm
4 sheets max. (include original)
Paper Insertion
(9)
(1 0) Line Spacing
Print Direction................................
(1 1)
(1 2) Line Feed Repeat Rate
Ribbon..
(1 3)
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Rear
1/6”, 1/8” or programmable
Bidirectional printing with logical seeking.
In bit image and double-strike mode, unidirectional printing from
left to right is selected when the power is ON.
Bidirectional printing is also possible using ESC U.
120 ms/line (when 1/6” line feed is performed intermittently)
100 ms/line (when 1/6” line feed is performed continuously)
Exclusive cartridge ribbon (Black)
1-2
Table 1
1-3
1.4 Major Components
The LQ-1500 consists, in a broad classification, of the following five major components
(I ) Housing
(2) Model-3660 printer mechanism
(3) Control circuit boards
(4) Interface circuit boards
(5) Power supply circuit boards
The housing of the LQ-1500 consists of an upper case and lower case. The lower case is designed to
facilitate mounting of the following components.
Circuitry for the LQ-1500 is located on five different boards: the UXFIL and UXPS/PSU 24E boards which
house the power supply; the UXMCL board, which contains most of the control circuitry; the UXDRV,
which handles print mechanism drive circuitry, and a interface board (IUPIF or IURS or IUIE) which serves
as computer interface.
1-4
(1) Housing (Fig. 1 .1)
Fig 1 .1 Upper and lower cases
(2) Model-3660 printer mechanism (Fig. 1.2)
The mechanism is an assembly of all the mechanical components including two stepper motors, a print
head, a ribbon feeding mechanism, a carriage assembly, sensors, and a frame section. One stepper
motor operates the print head carriage,
while the other works as the paper feed motor. The
Model-3660 is designed to permit easy maintenance.
‘Fig. 1.2 Model-3660 printer mechanism
(3) Contrl circuit boards (Fig. 1.3)
The control circuit is distributed between two circuit boards, the UXMCL and UXDRV.
The UXMCL circuit board performs the central processing, and the UXDRV circuit board drives the
Model-3660 printer mechanism.
Fig. 1.3 Control circuit boards
1-5
(4) Interface circuit boards (Fig. 1 .4)
An interface circuit board exchanges data between the host computer and UXMCL circuit board.
Fig. 1.4 Interface circuit board
(5) Power supply circuit boards (Fig. 1.5)
The power supply circuit of the LQ-1500, consists of two major components, the UXFIL and UXPS/
PSU 24E circuit boards. Both circuit boards are located in the rear righthand corner. The UXPS/PSU
24E circuit board supplies DC +24V, +12V, -12V and +5V to the control circuit and the interface circuit.
Fig 1.5 Power supply circuit board (100/120V version)
Fig 1.6 Power supply circuit board (220/24OV version)
1-6
CHAPTER 2
PRINCIPLES OF OPERATlON
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2.1 General
2.2 Connection
2.3 Connector Pin Assignment
2.3.1 Connector on UXMCL circuit board
2.3.2 Connector on UXDRV circuit board
2.3.3 Connector on UXPS/PSU 24E circuit board..
2.4 Electrical Circuit
2.4.1 Power circuit
2.4.2 Reset circuit
2.4.3 Sensor circuit.. ............................................................................
2.4.4 Carriage motor control circuit..
2.4.5 LF motor control circuit
2.4.6 Head driver circuit.
2.4.7 Auto sheet load circuit
2.4.8 Other function
2.5 Printer Mechanism
2.5.1 Operation
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Diagram ............................................................................
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2-1
2-1
2-3
2-3
2-8
2-12
2-13
2-13
2-22
2-22
2-26
2-34
2-37
2-39
2-40
2-41
2-41
2.1 General
This chapter provides the descriptron of signals at the various connectors electrically interconnecting such
major components as printer mechanism, control circuits, interface circuit, power supply circuit, and control pannel of EPSON LO-1500 Terminal Printer, and explains the operating principles of the various mechanism around the electric circuit of the printer.
2.2 Connection Diagram (Fig. 2.1)
Fig. 2.1 Connection diagram
2-1
The CPU Z-80A provides overall control of the LQ-1500. In addition the LQ-1500 is supported by two
slave CPUs: the 8042(8742), which controls the carriage motor; the 8041(8741), which controls the
paper feed motor.
Other major LSls include:
8255AC5
,,._,_..,.,_.,........_._......_
Output port for head pin drive data
8259A _..........._....__................... Interrupt controller
8253-5 .___................_................ Timer counter
2764(231 28)
uPD41 6-3
uPB6101 -009
.._._..._.....___....._.
,.,,...,, ,,,,_....,.,,._.,__...
,......._........_.._....
ROM which stores control programs and character patterns
RAM which is used as the input data and print data buffer
Gate array which controls LSls by receiving control signals
from CPU Z-80A
Fig. 2.2 Block diagram
2.3 Connector Pin Assignment
2.3.1 Connector on UXMCL circuit board
1) Table 2.1 CN1 pin assignment
(a) Use
(b) Number of pins
,,.,.......,,....,.,..,.............._............
._,.,,..._.._...,,,,......_._..
Table 2.1 Pin assignment (CN1 of UXMCL)
Used for data exchange between the main circuit board and the
interface circuit board
50
2-3
Note: “Direction” refers to the direction of signal as viewed from the UXMCL circuit board
2) Table 2.2 CN2 pin assignment
(a)
Use . . . . . . . . . . . . . . . . . .
(b) Number of pins
.._.........................
Table 2.2 Pin assignment (CN2 of UXMCL)
Data exchange between the main circuit board UXMCL and the
driver circuit board UXDRV.
50
2-5
2-6
3) Table 2.3 CN3 pin assignment
(a) Use . . . .
(b) Number of pins
..__..................__....,,..._........._..
_,,.._.._.,,,.._._,,..r....__._
Table 2.3 Pin assignment (CN3 of UXMCL)
To supply power from the power supply board UXPS/PSU 24E to
the main circuit board UXMCL.
9
Note: “Direction” refers to the direction of signal as viewed from the UXMCL circuit board.
4) Table 2.4 CN4 pin assignment
(a) Use
,....,,...,.._...__.....__..._,.,,,_.,...._...._..
Signal exchange between the control panel on the UXMCL circuit
board.
(b) Number of pins _...,,...,,_,,,........._...... 8
Table 2.4 Pin assignment (CN4 of UXMCL)
Note: “Direction” refers to the direction of signal as viewed from the UXMCL circuit board.
2-7
5) Table 2.5 CN5 pin assignment
(a) Use
___...__....__..._.._.._._..._.__.................
Exchange of head/home position signals between the printer me-
chanism Model-3660 and the main circuit board.
(b)
Number of pins
4
Table 2.5 Pin assignment (CN5 of UXMCL)
Note: “Direction” refers to the direction of signal as viewed from the UXMCL circuit board.
2.3.2 Connector on UXDRV circuit board
1) Table 2.6 CN1 pin assignment
(a) Use
(b)
._........_.......................................
Number of pins
To supply power from the power supply board UXPS/PSU 24E to
the driver circuit board UXDRV.
4
Table 2.6 Pin assignment (CN1 of UXDRV)
2) Table 2.7 CN2 pin assignment
(a)
Use
(b) Number of pins
.._.._._._...._._......_...._...
__..._._._.._.__..._......_....
Table 2.7 Pin assignment (CN2 of UXDRV)
Data exchange between the driver circuit board and the
Model-3660 printer mechanism.
34
2-8
Note: “Direction” refers to the direction of signal as viewed from the UXDRV circuit board.
2-9
3) CN3 pin assignment
Refer to Table 2.2.
4) Table 2.8 CN4 pin assignment
(a)
Use
Exchange of carriage motor signals between the drive circuit board
and the Model-3660 printer mechanism.
(b)
Number of pins .._............
18
Table 2.8 Pin assignment (CN4 of UXDRV)
Note: “Direction” refers to the direction of signal as viewed from the UXDRV circuit board
5) Table 2.9 CN5 pin assignment
(a) Use.
(b) Number of pins
.,.,.,,,....,..,.........__......................
,._._........._...__...........
Table 2.9 Pin assignment (CN5 of UXDRV)
Exchange of control signals between the drive circuit board
and the Model-3660 printer mechanism for paper feed motor or
paper hold release plunger.
12
6) Table 2.10 CN6 pin assignment
(a)
Use . . . . . .._.._...................
(b)
Number of pins .._....................
Table 2.10 Pin assignment (CN6 of UXDRV)
7) Table 2.11 CN7 pin assignment
(a)
Use .._.._..._...................
(b) Number of pins
Table 2.11 Pin assignment (CN7 of UXDRV)
To supply power to the fan set UA from the driver circuit board.
2
onnectlon of the driver circuit board and the ceramic resistance
C
2
2-11
2.3.3 Connector on UXPS/PSU 24E circuit board
1) CN1 pin assignment
AC power is supplied from UXFIL circuit board
2) CN2 pin assignment
Refer to 2.3.1 3) Table 2.3
3) CN3 pin assignment
Refer to 2.3.2 1) Table 2.6
4) Table 2.12 CN4 pin assignment
(a) Use
____..__...,,.,.,..._.._..._._..,..._._..._...,_._
To supply power from the UXPS/PSU 24E circuit board to the fan
set UB.
(b) Number of pins
,.___._..__.,_,,._._..._.._....
2
Table 2.12 Pin assignment (CN4 of UXPS/PSU 24E)
2-12
2.4 Electrical Circuits
2.4.1 Power circuit
Overview
The power supply circuit of the LQ-1500 consists of a fuse and filter circuit and power supply circuit.
The output voltages are +5, +12 and -12V for logic circuits and +24V for printer drive.
The power supply circuit, employs a switching power supply system in which the input voltage is directly
rectified for use.
Table 2.13 Voltage utilization
[A] 100V/120V version circuit
1.
Norse filter circuit (100/120V version)
Fig. 2.3 Noise filter circuit
The noise filter circuit IS mounted on the UXFIL board together with the fuse. Incoming AC flows through
the power switch and fuse before being filtered by a noise suppression circuit on the UXFIL board. The
filter circuitry limits electrical interference both to and from the printer.
2-13
2.
Rectifying circuit and inrush current prevention circuit
(100/120V version)
Fig. 2.4 Rectifying circuit and inrush current prevention circuit
In this power supply system, the AC input is directly rectified by the diode bridge DB1 and the output
voltages are as shown above.
An explosion-proof valve is provided in the upper part of the case of smoothing condenser Cl. If an abnormal voltage is applied to Cl, the explosion-proof valve will open, rendering the part inoperative.
In this power supply system, an inrush current flows at power on. Immediately after power on, when
Cl is not charged, an excessive charging current that may flow can cause the trouble of fuse F1 or
DB1. To prevent it, RI limits the inrush current. In other words, Cl is charged through RI at the time
of power on. With the start of power supply, a voltage is generated at the output of transformer T1,
and this is rectified by D11 and thyristor CY1 IS triggered. Now the thyristor shorts both the ends of
RI, thus completing the action of preventing Inrush current. The thyristor is conducting electricity as
long as the power supply is on.
When the thyristor does not conduct electricity because of some trouble, the power supply remains nor-
mal, but R1 gets heated abnormally. Also, RI may sometimes be disconnected when fuse F1 is blown.
3.
Converter circuit (100/120V version)
Fig. 2.5 Converter circuit
2-14
In this circuit, transistors Ql and Q2 alternately supply current to the windings of transformer T3, producing AC voltage as the output. 50/60 Hz input is frequency converted into 20 kHz through the action of
pulse transformer T3. This circuit starts oscillating automatically at about 20 kHz by transformer T2. With
the power supply on, R35 causes the base current to flow and either Q1 or Q2 turns on. Once started, the
base current is supplied from windings a and b, so that the transistor, which has been off, turns on instantly. T2, which is a current transformer, is in a positive feedback connection. 1 /10 of the collector current
from windings c and d as the base current. Oscillation frequency is determind by the length of time it takes
the core of T2 to become magnetically saturated after excitation from windings a and b.
When this occurs, the transistor which has been of opposite polarity is generated at T3.
Winding e adds this voltage to the base current and thus prepares the transistor which has been off, to turn
on. Then oscillation continues, with the trigger voltage from winding e applied to Q1 and Q2 alternately.
R4 limits the current that flows to winding e.
The voltage drop caused by R6 and D1 is smoothed by C4 to produce an inverse bias voltage when Q1 or
Q2 turns off. D3 and D4 are used as the by-pass when part of the magnetic energy is returned to the input
power. D5 and D6 clamp the spike voltage generated by T3 at switching to the DC input voltage via R5
and C20.
The clamp voltage is about twice as large as the DC input voltage. C21 reduces the transitional switching
loss of Q1 and Q2. Q1 and Q2 are parts most liable to develop failure.
Note: When troubleshooting the power supply, Q1 and Q2 should be among the first check points. When
either of these transistors are isolated as a trouble source, both must be replaced. Replacing only
one of the transistors can result in continued problems.
4. Power transformer circuit (100/120V version)
The variable leakage transformer not only performs power transformation by insulating the load from
higher voltage, but also stabilizes the output voltage by controlling the current flow to the control winding.
The VLT raises the DC output voltage by sending DC current into control winding f. From this current, the
VLT outputs a stabilized waveform.
With 20 kHz AC voltage applied to the input windings a and b, the pulse-width controlled AC voltage can
be obtained from the windings c and d. The winding e, which is an auxiliary power source of about 9V, is
used to drive the control winding f.
Fig. 2.6 Power transformer circuit
2-15
5.
+24V output circuit (100/120V version)
Fig. 2.7 +24V output circuit
The +24V output circuit is capable of supplying an average current of 6A. In this circuit, the pulse-width
controlled voltage from VLT is rectified and smoothed. The output which is a pulse voltage, rectified by
DB2 is smoothed by choke coil T4 and C2, so a continuous load current flows.
T4, excited by the output voltage of DB2, stores magnetic energy. When the current stops flowing from
the VLT, T4 discharges the magentic energy, so the load current flows continuously.
C22 and R3 prevent the spike voltage from occurring as a result of rectification. L2 and C3 constitute a
spike prevention filter.
6. Output control circuit (100/120V version)
Fig. 2.8 Output control circuit
In this circuit, the output voltage is detected and the output is stabilized by controlling the current flowing
to the control winding f of VLT. The current to the control winding is supplied from e, which is the auxiliary
power source, and is driven by Q3 and Q7.
The output voltage is detected by zener diode ZD1 A constant output voltage is maintained which adjusts
the base current of Q7 as assuring a constant current flow to ZD1
If too much current flows to winding f as a result of machine malfunction, the system is short curcuited,
winding f is cut off and output drops below 12V.
R22 and C23 advance the phase so as to maintain a stable output voltage. L1 and C14 constitute and auxiliary power source smoothing filter.
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7.
Output cutoff circuit (100/120V version)
Fig. 2.9 Output cutoff circuit
The output cutoff circuit is activated when the PSC signal is input or 30V or more is output as a result of a
malfunction.
When the thyristor CY2 is kept on, Q13 turns on Q12 and stops the base current of Q3, so that power is
not supplied to the control winding of VLT. Then +24V output is shorted by triggering the thyristor CY3.
A PSC signal is output due to failure of a printhead drive transistor.
8. DC-DC converter (100/120V version)
C9-Cll
Fig. 2.10 DC-DC converter circuit
In this circuit, outputs of +5, +I 2 and -12V are produced from +24V.
This circuit starts oscillating automatically at power on.
As the base current flows through R31 and Q4 turns on. With winding c excited, an electromotive force is
generated in winding b. Q4 turns on quickly because positive feedback of the voltage in winding b is made
to the base current of Q4.
With Q4 switched on, the current flowing to winding c continues increasing until it is restricted by the base
current value.
Q4 is turned off quickly by a counterelectromotive force generated in winding b, when increase in collecter
current stops.
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The magnetic energy stored in transformer T5 during the ON period is discharged to the load side during
the OFF period. When the magnetic energy is discharged, the counterelectromotive force in winding b is
lost and Q4 starts turning on again. The output is stabilized by controlling the average current flowing to
the winding c.
As +5V output begins to rise, the current flowing into the winding c is reduced, and as it begins to drop, the
current flowing into the winding c is increased. These controls are performed with Q10 shunting the base
current flowing to Q4. The voltage detector TL1 adjusts the base current of Q10 to maintain the +5V output constant.
The oscillation frequency of the circuit lowers with more lead current or rises with less load current.
Under no load, the oscillation becomes intermittent. Normally the circuit operates at about 30 kHz.
D10 and C13 rectify and smooth the base voltage of Q4.
D13, which is a two-way zener diode, clamps the surge voltage generated by T5 to 68V to protect Q4.
VR1 is used to set the +5V output voltage.
9. +5V output circuit (100/120V version)
+5V output is used for the logic circuit.
The current flowing through DB3 charges C9 through 11. The extremely large current value, however
causes a large output voltage ripple which is smoothed by Ls and C12.
10. 12V output circuit (100/120V version)
12V output, which is not stable, is used by RS-232C.
Since the DC-DC converter stabilizes the output by detecting +5V, the output voltage drops to about 5V
when +5V is under no load.
11. Vx. PWD circuit (100/120V version)
Fig. 2.11 Vx. PWD
Vx is output when +5V and +24V voltages become stabilized and is used to prevent the misoperation of the
printer when the power supply is turned on or off.
+5V make from +24V, retains the stable condition longer than +24V. Therefore, Vx is output when the
+24V output is +21 V or above.
A voltage drop on the +24V line due to a power failure or machine malfunction turns Q11 on and triggers
the PWD signal. When PWD is output the CPU is reset and the printer is stopped.
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