Commodore Computers PC 1901 User manual

SERVICE MANUAL
PC 1901
MONOCHROME MONITOR
APRIL, 1987 PN-314970-01
Commodore Business Machines, Inc.
1200 Wilson Drive, West Chester, Pennsylvania 19380 U.S.A.
Commodore makes no expressed or implied war-
ranties with regard to the information contained
herein. The information is made available solely on
an as is basis, and
the entire risk as to quality and
accuracy
is with the user. Commodore shall not be
liable for any consequential or incidental damages
in
connection with the use of the information con-
tained herein. The listing
of any available replace-
ment part herein does not constitute in any case
a recommendation,
warranty or guaranty as to
quality or suitability of such replacement part.
Reproduction or use
without expressed permission,
of editorial or pictorial content, in any matter is
prohibited.
This manual contains
copyrighted and proprietary information. No part
of this publication may be reproduced, stored in a retrieval system, or
transmitted in any form or by any means, electronic, mechanical,
photocopying, recording or otherwise,
without the prior written permis-
sion
of Commodore Electronics Limited.
Copyright © 1987 by Commodore Electronics Limited.
All rights reserved.

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1901 SERVICE MANUAL
IMPORTANT SAFETY NOTICE
Proper service and repair is important to the safe, reliable operation of all NAPCEC Equipment. The
service procedures recommended
by NAPCEC and described in this service manual are effective
methods of performing service operations. Some of these service operations require the use of tools
specially designed
for the purpose. The special tools should be used when and as recommended.
It is important to note that this manual contains various CAUTIONS and NOTICES which should be
carefully read in order to minimize the risk of personal injury to service personnel. The possibility ex-
ists
that improper service methods may damage the equipment. It also is important to understand
that these CAUTIONS and NOTICES ARE NOT EXHAUSTIVE. NAPCEC could not possibly know,
evaluate and advise the service trade of all conceivable ways in which service might be done or of
the possible hazardous consequences of each way. Consequently, NAPCEC has not undertaken any
such broad evaluation. Accordingly, a servicer
who uses a service procedure or tool which is not recom-
mended
by NAPCEC must first satisfy himself thoroughly that neither his safety nor the safe opera-
tion
of the equipment will be jeopardized by the service method selected.
WARNING
Critical components having special safety characteristics are
identified
with an S by the Ref. No. in the parts list and enclosed
within a broken line* along with the safety symbol A on the
schematics or exploded views.
Use of substitute replacement parts which do not have the same
specified
safety characteristics may create shock, fire, or other
hazards.
Under no circumstances should the original design be modified
or altered
without written permission from the N.A.P. Consumer
Electronics Corp. NAPCEC assumes no liability, express or
implied, arising
out of any unauthorized modification of design.
Servicer assumes all liability.
*Broken line:
© 1986 NAPCEC

..._..... _._ ... _._------
1901 SERVICE MANUAL
TABLE OF CONTENTS
TITLE PAGE
SPECIFICATIONS .................................................. .
SAFETY
GUiDELINES................................................ 2
CIRCUIT
DESCRiPTION............................................... 4
ADJUSTMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
CHASSIS
REMOVAL................................................. 5
PICTURE TUBE REMOVAL. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 5
MEASUREMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
PARTS
LIST....................................................... 7
PCB LAyOUT...................................................... 10
SCHEMATIC DIAGRAM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 12
CAUTION
USE A SEPARATE ISOLATION TRANSFORMER FOR THIS UNIT WHEN SERVICING.

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1901 SERVICE MANUAL
PC 1901
MONOCHROME MONITOR
(NAP -7BM613)
SPECIFICATIONS
Picture Tube: 12" measured diagonally with
glare reducing surface treatment
Deflection Angle: 900
Phosphor Type: P39 Green (BM7513, 7BM613)
LA Amber (BM7523, 7BM623)
Video Input Signal: TTL level digital video, separate
horizontal and vertical syncs.
(7BM613, 7BM623)
Video Amp Bandwidth: 20MHz
Horizontal Resolution: 800 lines (BM7513, BM7523)
1,000 lines (7BM613, 7BM623)
Character Field: 25 lines of 80 characters (2,000 total)
Power Supply: 120Vac ± 10%, 50-60Hz
Power Consumption: 30 Watts
Dimensions: 11.9"W x
11.1"0 x 10.9"H
*Subject to Modification
1

1901 SERVICE MANUAL
NAPCEC SAFETY GUIDELINES FOR THE
PROFESSIONAL SERVICE TECHNICIAN
Safety Checks
A fter the original service problem has been cor-
rected, a complete safety check should be made.
Be sure
to check over the entire set, not just the
areas where you have worked. Some previous ser-
vicer may have left an unsafe condition, which
could be unknowingly passed on to your customer.
Be sure to check all of the following:
Fire and Shock Hazard
1. Be sure all components are positioned in such
as way as to avoid the possibility of adjacent
component shorts. This is especially important
on those chassis which are transported to and
from the service shop.
2. Never release a repaired receiver unless all
protective devices such as insulators, barriers,
covers, strain reliefs, and other hardware have
been
installed according to the original design.
3. Soldering and wiring must be inspected
to locate possible cold solder joints, solder
splashes, sharp solder points,
frayed leads, pin-
ched leads, or damaged insulation (including ac
cord). Be certain to remove loose solder balls
and all
other loose foreign particles.
4. Check across-the-line components and other
components for physical evidence of damage
or deterioration and replace if necessary. Follow
original layout, lead length and dress.
5. No lead or component should touch a receiv-
ing
tube or a resistor rated at 1 watt or more.
Lead
tension around protruding metal surfaces
or
edges must be avoided.
6. Critical components having special safety
characteristics are identified with an S by the
Ref. No. in the parts list and enclosed within
a broken line* along with the safety symbol
on the schematics. Replacement parts without
the same safety characteristics may create
shock, fire or other hazards.
7.
When servicing any receiver, always use a
separate isolation transformer for the chassis.
Failure
to use a separate isolation transformer
may expose you to possible shock hazard, and
may cause damage to servicing instruments.
8. Many receivers use a polarized line cord (one
wide pin on the plug). Defeating this safety
device may create a potential hazard to the ser-
vicer and the user. Extension cords which do
not incorporate the polarizing feature should
never be used.
9. After re-assembly of the set, always perform
an ac leakage test or resistance test from
the line cord to all exposed metal parts of the
cabinet. Also, check all metal control shafts
(with knobs removed), antenna terminals,
handles, screws, etc. to be sure the set is safe
to operate without danger of electrical shock.
* Broken line: -. - . - - --
Implosion
1. All picture tubes used in current model receivers
are equipped
with an integral implosion system.
Care should always be used, and safety glasses
worn, whenever handling any picture tube.
Avoid scratching or otherwise damaging the
picture tube during installation.
2. Use only replacement tubes as specified by the
manufacturer.
X-radiation
1. Be sure procedures and instructions to all your
service personnel cover the subject of X-
radiation. Potential sources of X-rays in TV
receivers are the picture tube and the high
voltage circuits. The basic precaution which
must be exercised is to keep the HB at the fac-
tory recommended level.
2. To avoid possible exposure to X-radiation and
electrical shock, only the manufacturer's
specified anode connectors must be used.
3. It is essential that the service technician has
available
at all times an accurate HV meter. The
calibration of this meter should be checked
periodically against a reference standard.
4. When the HV circuitry is operating properly
there is no possibility of an X-radiation prob-
lem.
High voltage should always be kept at the
manufacturer's rated value-no higher-for op-
timum performance. Every time a color set is
serviced, the brightness should be run up and
down while monitoring the HV with a meter to
be certain that the HV does not exceed the
2

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specified value and that it is regulated correctly.
We suggest that you and your service techni-
cians review test procedures so that HV and HV
regulation are always checked as a standard
servicing procedure, and the reason for this pru-
dent routine be clearly understood by everyone.
It is important to use an accurate and reliable
HV meter. It is recommended that the HV
reading be recorded on each customers'
invoice, which will demonstrate a proper con-
cern for the customers' safety.
5. When troubleshooting and making test
measurements in a receiver with a problem of
excessive high voltage, reduce the line voltage
by means of a Variac to bring the HV into
acceptable limits while troubleshooting. Do not
operate the chassis longer than necessary to
locate the cause of the excessive HV.
6. New type picture tubes are specifically designed
to withstand higher operating voltages without
creating undesirable X-radiation. It is strongly
recommended that any shop test fixture which
is to be used with the new higher voltage
chassis be equipped with one of the new type
tubes designed for this service. Addition of a
permanently connected HV meter to the shop
test fixture is advisable. The CRT types used
in these new sets should never be replaced with
any other types, as this may result in excessive
X-radiation.
7. It is essential to use the specified picture tube
to avoid a possible X-radiation problem.
8. Most TV receivers contain some type of emer-
gency "Hold Down" circuit to prevent HV from
rising to excessive levels in the presence of a
failure
mode. These various circuits should be
understood by all technicians servicing them,
especially since many hold down circuits are
inoperative as long as the receiver performs
normally.
Leakage Current Cold Check
1. Unplug the ac line cord and connect a jumper
between the two prongs of the plug.
2. Turn on the power switch.
3. Measure the resistance value between the
jumpered ac plug and all exposed cabinet parts
of the receiver, such as screw heads, antennas
and control shafts. When the exposed metallic
part has a return path to the chassis, the reading
should be between 1 megohm and 5.2
megohms. When the exposed metal does not
have a return path to the chassis, the reading
must be infinity. Remove the jumper from the
ac line cord.
1901 SERVICE MANUAL
TO
INSTRUMENTS
O.151J
F
EXPOSED .-£-~--~~--~~
METAL PARTS
Leakage Current Hot Check
WATER PIPE
(EARTH GROUND)
1. Do not use an isolation transformer for this
test. Plug the completely re-assembled
receiver directly into the ac outlet.
2. Connect a 1. 5k ohm, 10 watt resistor paral-
leled by a 0.1 5uF. capacitor between each ex-
posed metallic cabinet part and a good earth
ground such as a water pipe, as shown above.
3. Use an ac voltmeter with at least 5000
ohms/volt sensitivity to measure the potential
across the resistor.
4. The potential at any point should not exceed
0.75 volts. A leakage current tester may be
used to make this test; leakage current must
not exceed 0.5 milliamps. If a measurement is
outside the limits specified, there is a possibility
of shock hazard. The receiver should be repaired
and re-checked before returning it to the
customer.
5. Repeat the above procedure with the ac plug
reversed. (Note:
An ac adapter is necessary
when a polarized plug is used. Do not defeat
the polarizing feature of the plug.)
Picture Tube Replacement
The primary source of X-radiation in this television
is the picture tube. The picture tube utilized in this
chassis is specially constructed to limit X-radiation
emissions. For continued X-radiation protection, the
replacement must be the same type as the original,
including
suffix letter, or an N.A.P. Consumer Elec-
tronics Corp. (NAPCEC) approved type.
Parts Replacement
Many electrical and mechanical parts in NAPCEC
television sets have special safety-related
characteristics. These characteristics are often not
evident from visual inspection nor can the protec-
tion afforded by them necessarily be obtained by
using replacement components rated for higher
voltage, wattage, etc. The use of a substitute
part which does not have the same safety
characteristics as the NAPCEC recommended
replacement part shown in this service manual may
create shock, fire or other hazards.
3

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CIRCUIT DESCRIPTION
This monitor
can be used as an alphanumeric and
graphic display unit for the home and personal com-
puters. The screen is anti-reflecting which means that
the legibility of the image
is extremely good. The
monitor has composite video signal input.
The monitor operates
on a supply of 120V, 60Hz ac.
The Power Transformer and CRT are mounted inter-
nally to the cabinet. The main panel has a Video
Preamplifier, Sync Channel, Vertical and Horizontal
Sweep Circuitry, Power Supply Horizontal AFC, and
Blanking Circuits. The On/Off control Video Gain Con-
trol and Brightness Control are mounted
on the main
panel and extend through the cabinet front. The circuit
adjustments are mounted to the main panel.
Power Supply
120 volt, 60Hz
ac operation. The ac section of this
receiver
is designed for operation on 120 volt, 60Hz
alternating current only. Never connect power cord to
a supply having a different frequency or voltage.
Overload Protection
This receiver incorporates a
.S amp Slow-Blow fuse and
a 2 amp fuse
in the ac circuit. These fuses provide pro-
tection to the chassis against certain electrical over-
loads.
5523 Horiz. 5ize-~;;;;:~
R406
Vert. Hold
1901 SERVICE MANUAL
ADJUSTMENTS
B+
Adjust (R106)
Connect dc voltmeter to the collector of
TS101 and
allow receiver and test equipment to warm up for
20
minutes. Using a non-metallic tool, adjust R106 to
obtain
11 Vdc ± 1% on voltmeter.
Focus (R336)
Adjust Focus Control for best overall detail
in the center
portion of the picture.
Horizontal Oscillator
Adjustment (R513)
Short
CS03 and R544 to ground. Adjust R513 for hori-
zontal stability of picture. Remove short between C503
and R544.
Vertical Size (R425)
Adjust the Vertical Size control (R425)
to fill the screen
vertically.
Horizontal Size (S523)
Adjust horizontal size to fill up screen.
Vertical Linearity (R423)
Adjust vertical linearity control for equal spacing of
horizontal lines
at the upper portion of the center of the
screen.
U102 Deflection Yoke
~--IPo'wer Transformer
---'---Video In
Adjustment Location -Rear View 4

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Chassis Removal
1. Remove six (6) screws, four (4) of which are securing
cabinet back
to cabinet front.
2. Lay cabinet face down on a soft material to protect
picture tube and cabinet finish.
3. Chassis Removal -Slide printed circuit board
assembly
to rear as far as leads will allow for ser-
vicing.
4. Place chassis on the heat sink of TS1 01. In this posi-
tion the monitor remains stable on the work bench.
5. Disconnect the picture tube socket and high voltage
anode lead
at picture tube.
6. Loosen clamp screw securing deflection yoke to pic-
ture tube. Slide the yoke to the rear until clear of
the neck of the picture tube.
Caution: Before removing high voltage lead at
picture tube, discharge picture tube highvoltage
anode
to ground only.
7. To replace components, reserve the above pro-
cedure.
8. Note: Backcover Replacement -Printed Circuit
Board must slide into propertracks in backcover.
-------------------------
1901 SERVICE MANUAL
Picture Tube Removal
1. Disconnect HV anode lead and picture tube socket
from picture tube. Loosen clamp screw securing
deflection yoke and slide yoke off neck of picture
tube.
2. Lay cabinet face down on a soft material so as not
to scratch or mar the face of the picture tube or finish
on cabinet.
3. Slide printed circuit board assembly out of track.
4. Remove screws from each of four (4) brackets hold-
ing picture tube
in place. Slip mounting wire over
neck of tube.
5. Using goggles and gloves, reach under face of tube
and lift from cabinet. Do not grasp neck
of picture
tube at any time.
6. To install picture tube, reverse the preceding steps.
Exercise caution not
to scratch face of picture tube.
CRT Board
T110 :
Power Transformer
--,~- --~~.~-- '
SK1
Power On/Off Switch
5

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'_.
MEASUREMENTS
Important
Read these instructions carefully and observe the con-
ditions noted when taking voltage readings or observ-
ing waveforms.
Picture tube high voltage anode may have a potential
10kV. Observe
all high voltage precautions when ser-
vicing the chassis.
Use safety goggles and gloves when
handling the picture tube.
Voltage Measurement Conditions Unless Otherwise
Specified
1. Voltages measured to chassis using a digital volt-
meter.
2. AC power source 120V, 60Hz line.
3. Voltage readings not in brackets taken using a pat-
tern generator (PM5519)
as a signal source.
4. Brightness control set at minimum, and contrast
control to maximum.
5. Voltage values shown are average readings. Varia-
tions may
be observed due to normal production
tolerances. Waveforms
1901 SERVICE MANUAL
Special Voltage Measurement Conditions
Picture tube anode voltage measured with VTVM high
voltage probe
at line voltage of 120 volts at 100llA beam
current.
Waveform Measurement Conditions
1. Waveforms taken using a pattern generator con-
nected
to the input plug of the monitor.
2. The video output signal of the generator adjusted
to 1 volt.
3. Brightness control and contrast control set at maxi-
mum.
General Schematic Notes -See
"Notes" on Sche-
matic Diagram
G)~I
40V
OV--
G /'\ iI I 22SV
-2SV-J L.J l
®"v-n I ® ®
10V
1/lIloV
ov __ l/l
I4v
ov--
0 0 0
4v_1/\12v
~I23v
ov_HI23v
ov-
e @
ov_J~I4v
(0 J\JLI
HI23v
l1V
ov--
OV
0
ov_V'1Isv
6