GE MAC 1200 User guide

MAC 1200
Servicing Instructions
Version 1.2
227 492 21 ENG Revision F
GE Medical Systems
Information Technologies

Caution:
During repairs/service interventions, observe the protective measures against damage due to
ESD.
GE Medical Systems Information Technologies considers itself responsible for the effects on
safety, reliability, and performance of the equipment, only if:
- assembly operations, extensions, readjustments, modifications, or repairs are carried out
by
GE Medical Systems Information Technologies or by persons authorized by GE Medical
Systems Information Technologies,
- the electrical installation of the relevant room complies with the applicable national and
local requirements, and
- the instrument is used in accordance with the instructions for use.
This manual contains service information; operating instructions are provided in the operator’s
manual of the instrument.
This manual is in conformity with the instrument at printing date.
All rights are reserved for instruments, circuits, techniques, and names appearing in the manual.
Trademarked names appear throughout this document. Rather than list the names and entities that own the
trademarks or insert a trademark symbol with each mention of the trademarked name, the publisher states
that it is using the names only for editorial purposes and to the benefit of the trademark owner with no
intention of improperly using the trademark.
900 SC, ACCUSKETCH, AccuVision, APEX , AQUA-KNOT, ARCHIVIST, Autoseq, BABY MAC, C Qwik
Connect, CardioServ, CardioSmart, CardioSys, CardioWindow, CASE, CD TELEMETRY, CENTRA, CHART
GUARD, CINE 35, COROLAN, CORO, COROMETRICS, Corometrics Sensor Tip, CRG PLUS, DASH,
Digistore, Digital DATAQ, E for M, EAGLE, Event-Link, FMS 101B, FMS 111, HELLIGE, IQA, IMAGE STORE,
INTELLIMOTION; LASER SXP; MAC; MAC-LAB; MACTRODE; MARQUETTE; MARQUETTE MAC;
MARQUETTE MEDICAL SYSTEMS, MARQUETTE UNITY NETWORK, MARS, MAX, MEDITEL, MEI, MEI in
the circie logo, MEMOPORT, MEMOPORT C, MINISTORE, MINNOWS, Monarch 8000, MULTI-LINK,
MULTISCRIPTOR, MUSE, MUSE CV, Neo-Trak, NEUROSCRIPT, OnlineABG, OXYMONITOR, Pres-R-Cuff,
PRESSURE-SCRIBE, QMI, QS, Quantitative Medicine, Quantitative Sentinel, RAC, RAMS, RSVP, SAM,
SEER, SILVERTRACE, SOLAR, SOLARVIEW, Spectra 400, Spectra-Overview, Spectra-Tel, ST GUARD,
TRAM, TRAM-NET, TRAM-RAC, TRAMSCOPE, TRIM KNOB, Trimline, UNITY logo, UNITY NETWORK, Vari-
X, Vari-X Cardiomatic, VariCath, VARIDEX, VAS, and Vision Care Filter are trademarks of GE Marquette
Medical Systems, Inc., registered in the United States Patent and Trademark Office.
12SL, 15SL, Access, AccuSpeak, ADVANTAGE, BAM, BODYTRODE, Cardiomatic, CardioSpeak, CD
TELEMETRY®-LAN, CENTRALSCOPE, Corolation, EK-Pro, EDIC, Event-Link Cumulus, Event-Link Cirrus,
Event-Link Nimbus, HI-RES, ICMMS, IMAGE VAULT, IMPACT.wf, INTER-LEAD, LIFEWATCH, Managed Use,
MARQUETTE PRISM, MARQUETTE® RESPONDER, MENTOR, MicroSmart, MMS, MRT, MUSE CardioWindow,
NST PRO, NAUTILUS, OCTANET, 02 SENSOR, OMRS, PHi-Res, Premium, Prism, QUIK CONNECT V. QUICK
CONNECT, QT Guard, SMARTLOOK, SMART-PAC, Spiral Lok, Sweetheart, UNITY, Universal, Waterfall, and
Walkmom are trademarks of GE Medical Systems Information Technologies, \nc.
Copyright 2002 GE Medical Systems Information Technologies GmbH

GE Healthcare
Service Calls and Product Support
Instructions
PN 403409-009
How To Reach Us...
To open a service call or obtain product support call the numbers below:
800.558.7044 (US & Canada)
Outside the US, contact your local GE representative or distributor.
For other product information please contact one of the offices listed on the
back cover of the manual.
Ordering Accessories and Service Parts
Ordering Manuals
Other Questions or Problems
Order accessories (leadwires, electrodes, recording papers, etc.) or service
parts (manuals, circuit boards, cables, software, etc.) from:
Accessories and Supplies
GE Healthcare
8200 West Tower Avenue
Milwaukee, WI 53223
Telephone: [phone] (US only)
414.355.5000 (outside US)
Fax: [phone]
Service Parts
GE Healthcare
P.O. Box 9100, 100 Marquette Drive
Jupiter, FL 33468-9100
Telephone: [phone] (US only)
561.575.5029 (outside US)
Fax: [phone] (US only)
561.575.5050 (outside US)
Have the following information available before calling:
part number of the defective part, or
model and serial number of the equipment,
part number/name of the assembly where the item is used, and
item name.
When ordering additional operator manuals, be sure to include the software
version of the product.
For additional information contact one of the offices listed on the back cover
of the manual or visit our website at http://www.gehealthcare.com.
403409-009H
5 January 2006
How to Reach Us 1

GE Medical Systems information Technologies
8200 W. Tower Ave., Milwaukee, WI 53223 U.S.A.
© 2006 General Electric Company. All rights reserved.
GE Medical Systems Information Technologies, a General Electric Company, going to market as GE Healthcare.
How to Reach Us 403409-009H

GE Medical Systems MAC 1200 V 1.2 Page 3
Information Technologies 227 492 21 Rev F
1
Device description 7
1.1 Block circuit diagram of entire instrument
12 Mechanical components 9
2 Functional description 11
21 Switching power supply 11
22 PCB NC Battery Charge 11
2.2.1 Charging circuit for the NC battery 11
2.2.2 Device behavior depending on the state of battery charge 12
23 PCB Control CS CI 12
2.3.1 Generation of internal power supplies 12
2.3.2 Switch On/Off circuit 13
2.3.3 ECG recording and front-end processing, 14
2.3.4 Controller core. 14
2.3.5 Real time clock 15
2.3.6 Memory 16
2.3.7 LCD graphics display interface 16
2.3.8 Keypad interface 17
2.3.9 Printhead control 17
23.10 Motor control 18
2.3.11 RS-232 interface 19
2.3.12 Buzzer 19
2.4 PCB Modem Supply CS M 19
2.5 Internal interfaces 19
2.5.1 Mechanical interfaces 19
2.5.2 Electronic interfaces 20
2.5.2.1 Interface to the switching power supply 20
2.5.2.2 Interface to the PCB NC battery charge 20
2.5.2.3 Interface to the LCD Graphics Display 22
2.5.2.4 Interface to the keypad 22
2.5.2.5 Interface to the printhead 22
2.5.2.6 Interface to the motor 23
2.5.2.7 Interfaces for production tests 24
2.5.2.8 Interface to PCB Modem Supply CS M 25
2.6 Interfaces to peripherals 26
2.6.1 Electronic interfaces 27
2.6.1.1 RS-232 interface 27
2.6.1.2 Patient input 28
2.7 Software Updates 29
2.8 Limitations 29
3 System test functions 31
3.1 General information 31
3.2
Test
start
31
3.3 Display test 32
3.4 Keyboard test
33

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Information Technologies 227 492 21 Rev F
3.5 Motor test 33
3.6 Test results 34
3.7 Self-test 34
3.8
Recording test 35
3.9 V24 tests 35
3.10 Time and date 37
3.11 Electrode test 37
3.12 Time constant 38
3.13 Setting the device model 38
3.14 Switching over the program for interpretation 40
3.15 Pace enhance 41
3.16 Serial number 41
3.17 ACI-TIPI 41
4 Repair instructions 43
4.1 Safety instructions 43
4.2 Replacing components 43
5 Troubleshooting tips 47
6 Adjustment instructions 51
7 Servicing and maintenance 53
7.1 Technical inspection 53
7.1.1 Visual check 53
7.12 Test functions 54
7.1.2.1 Recommended testing instruments and accessories 54
7.1.2.2 Test preparations 54
7.1.2.3 Operating and display unit performance tests 54
7.1.2.4 Test for recording speeds 25 and 50 mm/s 55
7.1.2.5 Device Test result check 55
7.1.2.6 RS-232 interface test 55
7.1.2.7 Analysis of the ECG signals and HR value 55
7.1.2.8 Pacemaker identification test 56
7.1.2.9 Identification of disconnected electrodes 57
7.1.2.10 Checking the charge status of the NC battery 57
7.1.3 Safety Analysis Tests 57
7.1.3.1 General information 57
7.1.3.2 Protective Earth Resistance Test 58
7.1.3.3 Measurement of Leakage Current 58
7.1.3.3.1 Enclosure Leakage Current Test 58
7.1.3.3.2 Patient Leakage Current Test. 59
7.2 Maintenance, cleaning, disinfection 60

GE Medical Systems
Information Technologies
8 Parts List
9 Specifications
MAC 1200 V 1.2
227 492 21 Rev F
Page 5
61
65
10 Device Documents
73

GE Medical Systems
Information Technologies
Revision History
MAC 1200 V 1.2
227 492 21 Rev F
Page 6
Each page of this manual has the document number followed by a revision letter, located
at the top of the page. This letter identifies the manual update level. The latest letter of the
alphabet corresponds to the most current version of the document.
The revision history of this manual is summarized below.
Date ECO No Revision
March 05,1999 -- Α
May 10, 1999 062 136 B
June 29, 1999 062727 C
February 4, 2000 062920 D
January 9, 2002 068851 F
Remarks
V 1.0, initial release
Software Package for
MAC 1100/1200 (Software change) page
55, new MRI
Pin 4— Coding pin, page 19,
Supplementation to chapter 3.4; page 29
Software Release V 5.02 page 55,new MRI,
PCB Control CS CI, Sheet 9 new Index
PCB Control CS C, new Index
PCB Battery Charge CS CI, new Index
Device Version V1.1 with Remote
Start Input, internal Modem Supply and
Software Release V5.1
Software Release V5.21 for MAC1200

GE Medical Systems MAC 1200 V 1.2 Page 7
Information Technologies 227 492 21 Rev F
1 Device description
This Service Manual describes device version V1.2 of MAC1200
The MAC 1200 is portable electrocardiograph with an integrated printing unit.
it is used to acquire, record and process ECG signals.
It is designed for line-power and battery operation. A power supply and battery with a
charging circuit are integrated into the instrument.
The integrated LCD graphics Display shows 3 ECG channels. It also displays status
information, filter settings, speed/format, gain and the status of the electrodes.
With the setup feature, the user is able to setup the device and the modes for his own
needs.
The patient cable for the acquisition of ECG signals is connected by means of a 15-pin
connector as used with MAC 500. Patient cables used with MAC 1000 cannot be
connected to the MAC 1200.
In Automatic Mode, the acquired ECGs can be transmitted to MUSE or a PC via an RS-232
interface. With the additional option Patient Memory, all acquired ECGs can be transmitied.
MAC1200 with version V1.1 has all features of the version V1.0 described above,
additionally version V1.1 has a Remote Start Input, an internal Modem Power Supply
and the new Software Release V5.1.
Device Part number Name Supply Voltage Remarks
Version
V1.2 101 168 23 MAC 1200 95 ... 240V ac US version
Hardware functional blocks:
The hardware comprises the following main functional blocks:
m Switching power supply
m NC Battery
m PCB NC Battery charge
m PCB Control CS CI
m PCB Modem Supply CS M
E Printing unit
m Keypad
= % VGA graphics display, monochrome

GE Medical Systems
Information Technologies
MAC 1200 V 1.2 Page 8
227 492 21 RevF
1.1. Block circuit diagram of entire instrument
MAC1200 (US), Version V1.1
| |
PCB Modem Supply
Modem Supply
Programm
Memory
Boot
Internal
ECG RAM
Loader
RAM
buffered
Configuration
ECG
Input
Line
Power E
Input
RS232 | | RS232
Memory Driver Interface
Keypad
Interface Keypad
Display LCD Graphics Display
ECG Interface 1/4 VGA Monochrome
AS Display
Acquisition Controller Supply
"| and Core
Conditioning
Motor
Control Motor
Real Time
Clock Thermal i
buffered Pinthead Thermal Printhead
Control
Printing Unit
Logic Supply
+5V_+3.3V ,
Device
Analog Supply On/OFF
Printhead Control
Supply
PCB Control CS CI
Line Power
Input ーー] NC Battery
with Fuse
Ñ MAC1200 (US)
Switching PCB
Power Supply NC Battery V 1.1
+26,5V Charge 14.01.2000
Line Power, NC Battery

GE Medical Systems MAC 1200 V 1.2 Page 9
Information Technologies 227 492 21 Rev F
12 Mechanical components
The main mechanical components comprise the upper and lower shell of the MAC1200
The lower shell serves as a basic unit to receive the following assemblies:
mM Line power input module with fuse
m Switching power supply
m NC Battery
m PCB NC Battery Charge
m PCB Control CS Ci
m PCB Modem Supply CS M
m Graphics display
m Thermal printing unit
m Paper container
The upper shell accommodates the keypad, which is connected to the PCB Control CS Ci
via a 26-pin connector.
The MAC 1200 can be opened by releasing 5 screws at the bottom of the lower shell,
opening the paper flap and lifting up the upper shell a little bit to remove the keypad cable
from the PCB Control CS CI. The upper shell then can be removed completely.
To replace the NC Battery, the battery flap at the bottom of the lower shell must first be
unlocked with a screw-driver before it can be removed.
The 15-pin input connector to connect the patient cable and the 9-pin connector for the
RS-232 interface are iocated directly on the PCB Control CS CI.

GE Medical Systems MAC 1200 V 1.2 Page 10
Information Technologies 227 492 21 Rev F

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Information Technologies 227 492 21 Rev F
2 Functional description
The block circuit diagram of the entire instrument in Section 1.1 and the functional blocks of
circuit diagram sheets (P-plans) describe the individual functional blocks.
2.1 Switching power supply
The switching power supply generates the fundamental device voltage for the PCB Control
CS Ci and for the PCB NC Battery Charge.
It has the following input specifications:
Input voltage range: 85 ... 264V ac
Line frequency range: 47 ... 65 Hz
The output voltage is +26.5 V dc, the maximum load is 1.5A.
2.2 PCB NC Battery Charge
MAC 1200 can operate battery powered. With a new, fully charged NC battery, in
Automatic Mode up to 50 ECG can be recorded.
The PCB NC Battery Charge, controls and monitors the charging process, depending on
the status of the battery and the status of the device.
2.2.1 Charging circuit for the NC battery
An integrated charging device is used to charge the battery. During charging it monitors the
battery voltage function and switches over from rapid charging to trickle charging.
Applying the line power to the MAC 1200 , or insertion of the battery activates the charging
circuit.
During a recording, the charging current is reduced.
In standby mode, a depleted battery is fully charged within 4 hours.

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Information Technologies 227 492 21 Rev F
2.2.2 Device behavior depending on the state of battery charge
Depending on the status of the battery and the status of the device, the following behavior
occurs:
State1: Battery depleted, line power supply is connected up:
Baitery charged in rapid mode; when fully charged, switchover to trickle
charging.
State 2: Battery full, line power supply is connected up:
Battery charged in rapid mode for some minuies till the charging circuit
recognizes “battery full", then switchover to trickle charging.
State 3: Battery depleted, no line power supply, device is switched on:
Device inoperative.
State 4: Battery full, no line power supply, device is switched on:
Device fully operative.
When battery is almost depleded, the LEDBAT signal is activated to
Indicate that the device should be charged by connecting to the line
power supply. If the operation is continued without line power, MAC
1200 will shut down itself when a minimum level is reached to prevent
the battery from a excessive discharge.
State 5: Battery depleted, line power supply is connected up, device is switched
on:
Battery is charged in rapid mode, device is fully operative, including
recording.
During recording, the charging current is reduced. If in this phase, a lot
of recordings take place, the battery is not fully charged within 4 hours.
2.3 PCB Control CS CI
The PCB Control CS_CI is the mainboard of the MAC 1200 and accommodates the control
functions of the device, except the line power supply and the NC battery-charging
controller.
2.3.1 Generation of internal power supplies
Logic power supply + 5V and + 3.3V
The processor core and the memory is a + 3.3V design.

GE Medical Systems MAC 1200 V 1.2 Page 13
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The interface functions to display, to RS-232, to the printing unit and to the ECG acquisition
unit are supplied with + 5V.
Both the + 3.3V and the + 5V are generated separately by a clock-rated voltage controller.
By using the ,adjustable version” of the voltage controller, both supplies are based on the
same voltage controller. The output voltage is determined by appropriate dimensioning of
the voltage divider at the feedback input of the voltage controller,
Standby supply + 5VSTB and + 3.3VSTB
The standby supply + 5VSTB supplies the ON/OFF Control, the + 3.3VSTB buffers the
patient ECG memory when the device is turned off.
Both supplies are generated together from one low-power linear regulator with low
quiescent supply current.
Analog supply + 12V
+ 12V is used for the heating control and temperature monitoring of the printing unit, which
requires only a current of a few milliamperes.
This supply is generated by a linear regulator with feedback input.
2.3.2 Switch On/Off circuit
The Switch On/Off Circuit consists of the On/Off Control and the Voltage Control.
The On/Off Control switches the device on or off by switching the device supplies
+UVERS and +USUPPSW.
The On/Off Control is supplied from the + 5VSTB.
Device On Sequence:
The transition from Device Off State, or Standby State when line power is connected to
Device On State can only be activated by pressing the On/Off button.
Device Off Sequence:
The transition from Device On State to Device Off State, or Standby State when line power
is connected can be achieved as follows:
mM pressing the On/Off button
m when the control core activates the signal DEV OFF,
E when the voltage control applies the signal REG OFF , because the battery voltage
gets too low during battery operation.

GE Medical Systems MAC 1200 V 1.2 Page 14
Information Technologies 227 492 21 RevF
The Voltage Control controls the battery voltage during battery operation.
The signal BATT_LEV2 indicates that the battery charge has gone down, and the device
should be connected to the line power soon.
The signal BAT_LEV1 indicates that the battery has been discharged almost completely,
the device should be connected to the line power immediately, otherwise the device will
shut down within few minutes.
If battery discharge is continued without connecting to the line power, the signal
REG OFF is activated and the device is switched off.
2.3.3 ECG recording and front-end processing
The patient input is classified as being cardiac floating and is defibrillation-proof.
The patient leads are connected with a 15-pin connector with a special form for the
specified and released patient cables for the MAC 1200.
The main element of the ECG recording and front-end processing is a set of chips
comprising 3 ASICs. Pace detection is realized by a separate circuit.
Every disconnected electrode is detected by a special AC measurement, which allows
higher impedance between electrode and patient.
N common-mode compensation ensures suppression of interference, at the same time
serving to improve the in-phase suppression of the input electrodes.
To protect patients, the ECG recording and front-end processing are assembled as floating
components. Digital signals from and to the controller core are transmitted via opto-
electronic couplers. The floating supply +/- 5V is generated by an isolated flyback converter
from the + 5V logic power supply.
2.3.4 Controller core
The actual core comprises the Motorola Power PC MPC821, which contains the following
integrated components:
m chipselect logic
m DRAM controller
m SCC and SMC for RS-232
m LCD controller
m SP! Interface

GE Medical Systems MAC 1200 V 1.2 Page 15
Information Technologies 227 492 21 Rev F
m 1/O ports
m Real-Time Clock counter register
In addition, the MPC821 contains a JTAG port with test and programming capabilities.
The MPC821 has the following additional power supplies:
ш VDDSYN, filtered from the + 3.3V logic supply, for the clock generation.
m KAPWR, generated from the + 3.3V logic supply, or from a battery when device is off,
used for buffering the RTC Counter Register.
The clock generation for the MPC821 is realized by a quartz oscillator with 32.768KHz.
The system clock CLOCKOUT is adjusted with the internal PLL register. The system
frequency is 25 MHz.
The Watchdog /Reset Generation is implemented separately in an integrated system
monitoring chip. lt has the following functions:
m Power-up reset for the MPC821 when the device is switched on
m Voltage monitoring of the + 3.3V and + 5V, with reset generation
8 Watchdog
EH Switchover to battery supply for patient ECG memory when device is switched off
m Signal for access protection for patient ECG memory when device is switched off
The Reset Configuration defines startup conditions like boot port size and clock
generation source.
Four LEDs indicate the device status in addition:
LED1: active when a HRESET_ occurs
LED2: indicator for the logic supply
LED3, LED4: indicate internal software states
The control register comprises device control signals to switch off the device, control
battery charging and display control signals.
The status register contains information on the device hardware configuration and the
state of the battery charge.
2.3.5 Real time clock
With Software V5.2, two options for the real time clock are supported. The software checks
for an external real time clock chip (X13 on PWA control). This chip is available with Index
G of PWA Control CS Cl and Index F of PWWA Control CS C.
If the external RTC is found, it will be used for the clock function. If not, the internal clock of
the MPC821 will be used. The external RTC is more accurate than the internal one. Both
clocks are buffered by the voltage KAPWR.

GE Medical Systems MAC 1200 V 1.2 Page 16
Information Technologies 227 492 21 RevF
2.3.6 Memory
The complete memory of the MAC 1200 is located on the PCB Control CS CI.
The software of the device can be loaded through the JTAG Port during the production
process, or for service purposes with the appropriate programming software through the
RS-232 interface.
Program Memory:
Type: Flash, + 3.3V supply
Organization: 1 Mbit x32, 4 Mbyte
Waitstates: 1 Waitstate
DRAM:
Type: EDO DRAM, + 3.3V supply
Organization: 1 Mbit x32, 4 Mbyte
Waitstates: 0 Waitstate
Patient ECG Memory:
Type: buffered SRAM, + 3.3V supply
Organization: 256 Kbit x16, 512Kbyte
Waitstates: 1 Waitstate
Configuration Memory:
The configuration memory is part of the program memory Flash. With special hardware
and software protection facilities, write access to the Flash is only possible in the defined
configuration memory of the Flash. Thus an external configuration Memory like an
EEPROM is not required.
2.3.7 LCD graphics display interface
For the LCD interface to the 4 VGA monochrome LCD interface, the internal LCD
controller of the MPC821 is used.
Controller Interface:
For the digital control signals, delivered from the MPC821, only an output driver is required.

GE Medical Systems MAC 1200 V 1.2 Page 17
Information Technologies 227 492 21 Rev F
LCD Power Supply:
The LCD power supply VEE of -23V is generated from the +5V logic supply. The
generation starts after HRESET_ becomes inactive to ensure that the logic supply of +5V
first is applied to the display.
Adjusting Contrast:
Contrast adjustment of the Display is accomplished with the contrast voltage VO. The level
of VO is controlled with the PWM signal BLCD_CONTR from the timer module of the
MPC821. In addition, the contrast voltage is temperature compensated.
Backlight:
The LCD backlight converter for the CCFL tube is located on the PCB Control CS CI too.
The backlight converter is generated from the +5V logic power supply.
The signal BLCD_ENBA switches the backlight on or off.
The user can define the backlight active time in the configuration menu.
2.3.8 Keypad interface
The keypad interface contains the control register for 8 keypad columns and the receiving
register for 7 keypad rows, and the control signals for the status LEDs: LED_LIN,
LED_BATT, LED_START and LED_STOP.
Using the matrix of 8 x 7, up to 56 keypads can be detected.
Identification of the key pressed is as follows:
The controller activates a column, activation is via low-level, then the row-register is read to
identify the pressed key by a low-level. This procedure is repeated with the next column, till
all columns have been activated.
2.3.9 Printhead control
The printhead controller takes on the complete control of the 216-mm thermal printhead
with a line width of 200 mm.
The output rate to the printhead is 1000 /sec. The resolution in the Y-direction is 8 dot/mm,
in the X- time axis up to 40 dots/mm.

GE Medical Systems MAC 1200 V 1.2 Page 18
Information Technologies 227 492 21 RevF
Thermal Printhead Dot Control:
The MPC821 prepares a complete dot column and sends it to the FIFO. A complex PLD
reads out a complete column of the FIFO and generates the digital control signals for the
printhead, which are shifted in series.
The duration of heating a dot column is defined through the pulse width of the PWM Signal
HEAT that is generated from the complex PLD too.
In addition, the duration of heating a dot column is influenced by the thermal printhead
monitoring.
Thermal Printhead Temperature Monitoring:
The thermal printhead temperature monitoring measures the temperature of the thermistor,
located on the printhead. A constant current source effects a temperature-dependent
voltage drop.
lf a printhead temperature of 55°C is exceeded, the signal REC_OVHEAT_ is activated
and the heating of the printhead is prevented by disabling the signal STROBE.
Only when the printhead temperature drops below 50°C is the signal REC_OVHEAT_
disabled and the heating via the signal STROBE re-enabled.
In addition, a continuous reduction of the heating duration occurs with increasing printhead
temperature, resulting in a regular typeface throughout the entire temperature range.
2.3.10 Motor contro}
Paper transportation for the speeds 5mm/s, 25mm/s and 50mm/s is driven by a stepping
motor. The stepping motor is controlled by an integrated stepping motor driver circuit. The
current for the motor is adjusted by the sense resistors of the stepping motor driver.
For the speed 5mm/s, the motor current is reduced, triggered by the signal LOW SPEED.
The motor speed is controlled by the frequency of the signal RECTMR STEP, which is
generated by the timer unit of the MPC821.
The driver circuit is enabled by the signal REC_MOTEN, the driver is powered from
+22,5V.