Zenith ZVM-131 User manual

SERVICE MANUAL
Color Video Monitors
Models ZVM-131/133/135/136
585-30'1 860-23-1

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LIMITED RIGHTS LEGEND
Contractor is Zenith Data Systems Corporation of S1. Joseph, Michigan 49085. The entire
document is subject to Umited Rights data provisions.
Copyright ©
1985 by Zenith Data Systems Corporation
Printed in the United States of America
Zenith Data Systems Corporation
St. Joseph, Michigan 49085
INITIALS

Characteristics ................................ 5
Description .................................... 5
Controls, Indicators, and Connectors. . . . . . . . . . . . . .. 5
ZVM-131 and ZVM-135 ....................... 5
ZVM-133 and ZVM-136
....................... 6
ZVM-131 Specifications.......................... 7
ZVM-133 Specifications . . . . . . . . . . . . . . . . . . . . . . . . .. 8
ZVM-135 Specifications . . . . . . . . . . . . . . . . . . . . . . . . .. 9
ZVM-136 Specifications . . . . . . . . . . . . . . . . . . . . . . . . .. 9
Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10
ZVM-131 and ZVM-135 Installation ............... 10
Composite Signal ........................... 10
RGB Signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 10
ZVM-133 and ZVM-136 Installation .. . . . . . . . . . . . .. 13
Circuit Descriptions .......................... 14
ZVM-131 and ZVM-135 Circuit Boards ............ 14
Main Board ................................ 14
Start-Up and Operating Voltages . . . . . . . . . . .. 14
Degaussing Circuit . . . . . . . . . . . . . . . . . . . . . . .. 14
Power Supplies .......................... 14
+150 VDC Supply ....................... 14
+ 26 VDC Supply ........................ 15
+ 12 VDC Supply ........................ 15
RGB Drive and Cutoff Voltages . . . . . . . . . . . .. 15
Composite Drive.... . . . . . . . . . . . . . . . . . . . . .. 15
Composite Vertical Sync . . . . . . . . . . . . . . . . .
.. 15
Composite Horizontal Sync . . . . . . . . . . . . . . . .. 16
Horizontal
and Vertical Drive Outputs .. . . . . .. 16
AudiolVideo Sync Board ..................... 16
High Voltage and Horizontal Sweep Board . . . . .. 16
Width Step Board . . . . . . . . . . . . . . . . . . . . . . . . . .. 16
Video Output Board ......................... 16
ZVM-133 and ZVM-136 Circuit Boards. . . . . . . . . . .. 17
RGB Gain Control Board . . . . . . . . . . . . . . . . . . . .. 17
RGB Input Signal. . . . . . . . . . . . . . . . . . . . . . . .. 17
RGBI Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 17
Servicing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18
Safety and Service Guidelines . . . . . . . . . . . . . . . . . .. 18
AC Leakage Test ............................. 18
Other Precautions ............................. 19
Suggested Tools and Supplies .................. 19
Test Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 19
Troubleshooting ............................... 19
Fault Isolation Procedures ...................... 20
CONTENTS
Alignments and Adjustments .................... 21
Main Board Adjustments ..................... 21
RGB Cutoff and G2 Adjustments. . . . . . . . . . .. 21
RGB Drive Adjustments ................... 21
Vertical Center and Vertical Height Adjustments. 21
Horizontal Center and Width Adjustments . . . .. 21
Horizontal Oscillator Adjustment . . . . . . . . . . . .. 24
+ 95 Volt Adjustment. . . . . . . . . . . . . . . . . . . . .. 24
Sweep Assembly Adjustments . . . . . . . . . . . . . . .
.. 24
Focus Adjustment
........................ 24
Width Selection .......................... 24
AudioNideo Sync Board Adjustments .......... 24
Chroma Null Phase Adjustment . . . . . . . . . . .
.. 24
BLUE and RED Cutoff Adjustments ......... 24
Cleaning Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . .. 26
Performance Tests ............................ 26
Fill the Screen Test . . . . . . . . . . . . . . . . . . . . . . . .. 26
Color Bar Test ............................. 26
BASIC Program ............................ 27
Servicing Diagrams
............................ 27
Disassembly/Reassembly ....... . . . . . . . . .. . . . .. 49
Back Cover. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 49
Top Cover .............................. 49
Video Output Board . . . . . . . . . . . . . . . . . . . . . .. 49
Input Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 49
High Voltage and Horizontal Sweep Assembly. 49
CRT .................................... 49
Primary Control Board . . . . . . . . . . . . . . . . . . . .. 49
AudiolVideo Sync Board . . . . . . . . . . . . . . . . . .. 50
Main Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 50
Speaker ......................... # • • • • • •• 50
Secondary Control Assembly (ZVM-131 and ZVM-
135) .................................... 50
RGB Gain Control Board (ZVM-133 and ZVM-136)
........................................ 50
Parts List ................................... 51
Figures
1. Monitor Front View ......................... 5
2. ZVM-131 and ZVM-135 Controls and Connectors. 11
3. ZVM-133 and ZVM-136 Controls and Connectors. 12
4. AC Leakage Voltmeter Circuit ............... 18
5. Main Board Adjustment~ .................... 22
6. High Voltage and Sweep BoardlWidth Step Board Ad-
justments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 23
Page 3

7. AudioNideo Sync Board Adjustments ......... 25
29. Video Output Board (Medium-Resolution) Schematics
8. Block Diagram ZVM-131 and ZVM-135 ........ 29
......................................... 46
9. Block Diagram ZVM-133 and ZVM-136 ........ 30
30. Primary Control Board A-12800 Component Location
10. AudioNideo Sync Board Component Location .. 31
......................................... 47
11. AudioNideo Sync Board Waveforms .......... 32
31. Primary Control Board A-12800 Schematic . . . .. 47
12. AudioNideo Sync Board Schematic . . . . . . . . . .. 33
32. Primary Control Board Schematic ZVM-131-135. 47
13. RGB Gain Control Board Component Location . 39
33. Secondary Assembly A-9522 Component Location
14. RGB Gain Control Board Waveforms ......... 39
......................................... 48
15. RGB Gain Control Board Schematic .......... 39
34. Secondary Assembly A-9522 Schematic ....... 48
16. Main Board Component Location .. . . . . . . . . . .. 40
35. Monitor Exploded View ..................... 89
17. Main Board Waveforms .... '" '" ........... 40
18. Main Board Schematic ..................... 41
Tables
19. High Voltage and Horizontal Sweep Board Component
1. General Troubleshooting .................... 20
Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 42
2. Monitor Major Assemblies .. . . . . . . . . . . . . . . . .. 52
20. High Voltage and Horizontal Sweep Board Waveforms
3. Cable Assemblies . . . . . . . . . . . . . . . . . . . . . . . . .. 53
......................................... 42
4. Main Board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 54
21. High Voltage and Horizontal Sweep Board Schematic
5. High Voltage and Horizontal Sweep Board . . . .. 67
......................................... 43 6.
Width Step Board ......................... 71
22. Width Step Board Component Location. . . . . . .. 44
7. Horizontal Output Transistor and Bracket Assembly
23. Width Step Board Schematic ................ 44
......................................... 71
24. High Voltage Power Supply Component Location. 44
8. High Voltage Power Supply Board . . . . . . . . . . .. 71
25. Video Output Board (High-Resolution) Component Lo-
9. High Resolution Video Output Board . . . . . . . . .. 72
cation
.................................... 44
10. Medium Resolution Video Output Board ....... 73
26. Video Output Board (High-Resolution) Waveforms
11. RGB Gain Control Board ................... 74
......................................... 45
12. AudioNideo Sync Board .................... 75
27. Video Output Board (High-Resolution) Schematic. 45
13. Secondary Control Assembly ................ 88
28. Video Output Board (Medium-Resolution) Component
Location . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
.. 46
Listings
1. BASIC Color Bar Program .................. 27
Page 4 Contents

Description
Color video monitors ZVM-131, ZVM-133, ZVM-135, and
ZVM-136 are very similar. They are the same size, have
the same appearance (see Figure 1), and use much of the
same circuitry. Their main circuit boards and most other
boards are similar. A monochrome display can be selected
with a switch on all models.
r~ --- __ -"
r5- ~-
I
Figure 1
Monitor Front View
The ZVM-131 and ZVM-135 color monitors, together with
their export versions, the ZVM-131-E and ZVM-135-E, can
accept both RGB and composite inputs from different
sources and have full audio capability. The ZVM-131 and
ZVM-135 are the same except that the ZVM-131 has a
medium-resolution display and the ZVM-135 has a high-
resolution display.
The high-resolution ZVM-133 and ZVM-136 color monitors,
together with their export versions, the ZVM-133-E and
ZVM-136-E, have no audio capability and their inputs are
limited to those computers with
an RGB output. The ZVM-
133 and ZVM-136 are the same except that the ZVM-136
has a high persistance phosphor CRT.
Characteristics
Controls, Indicators, and Connectors
Refer to Figures 2, 5, 6, and 7 for locations of controls, in-
dicators, and connectors.
ZVM-131 AND ZVM-135
Front Panel
Power switch
Power indicator
Volume
Display drive
Black level
Color level
Tint
Sharpness
Rear Panel
GREEN-WHITE switch
RGB/COMP switch
Focus
RGB input connector
Video input connector
Video output connector
Audio input connector
Audio output connector
Internal
Horizontal centering
Width
Horizontal oscillator
Vertical centering
Height
G1
G2
RGB cutoff (main board)
BLUE and RED cutoff (audio/video sync board)
RGB drive
+95 volts
Width selection
Chroma null phase
Black level cutoff
Black level reference
Page 5

ZVM-133 AND ZVM-136
Refer to Figures 3, 5~ 6f8nd 7 for locations.
Front Panel
Power switch
Power indicator
Brightness
Contrast
GREENIWHITE switch
Rear Panel
Focus
RGB connector
Page 6
Internal
Horizontal centering
Width
Horizontal oscillator
Vertical centering
Height
G1
G2
RGB cutoff
RGB drive
+95 volts
Width selection
Characteristics

ZVM-131 Specifications
CRT .......................................... .
Pixel resolution
................................. .
Text capacity
................................... .
Video resolution
................................. .
RGB input ..................................... .
Composite input
................................. .
Synchronization
................................. .
Bandwidth
...................................... .
Rise time ............................ , ......... .
Audio input
..................................... .
Audio output
................................... .
Height
............................... , ......... .
Width
Depth
Weight
........................................ .
Power
......................................... .
Characteristics
13" diagonal, medium-resolution color display
390 dots (RGB), 250 dots (composite)
25 lines
of 40 characters each
390 pixels horizontal by 240 lines (non- interlaced),
or by
480 lines (interlaced)
5 volts positive polarity digital signal
NTSC 1 volt unterminated,
or 75 ohm
terminated
± 1 volt to 5 volts horizontal
± 1 volt to 5 volts vertical
RGB: 6 MHz
Composite: 2.5 MHz
RGB: 70 nanoseconds
Composite: 100 nanoseconds
0.35 to 3.5 Vrms, 50
Kil, AC coupled
wired directly to Audio Input
13.75" (350 mm)
15.25" (390 mm)
15.25" (390 mm)
38 pounds (17.2 kg)
120 VAC, 60 Hz, 1.23A, (ZVM-131)
240 VAC, 50 Hz, 0.6A, (ZVM-131-E)
95 watts (ZVM-131 and ZVM-133-E)
Page 7

ZVM-133 Specifications
CRT .......................................... .
Pixel resolution ................................. .
Text capacity
................................... .
Video resolution
................................. .
RGB input ..................................... .
Composite input
................................. .
Synchronization
................................. .
Bandwidth
...................................... .
Rise time ...................................... .
Height
......................................... .
Width
Depth
Weight
........................................ .
Power
......................................... .
Page 8
13" diagonal, high-resolution color display (high persis-
tance CRT, ZVM-136 only)
640 dots
25 lines of 80 characters
640 pixels horizontal, by 240 lines (non- interlaced), or by
480 lines (interlaced)
5 volts positive polarity digital signal
NTSC 1 volt unterminated, or 75 ohm terminated
± 1 volt to 5 volts horizontal
± 1 volt to 5 volts vertical
20 MHz
70 nanoseconds
13.75" (350 mm)
15.25" (390 mm)
15.25" (390 mm)
38 pounds (17.2 kg)
120 VAC, 60
Hz, 1.23A, (ZVM-133)
240 VDC, 50 Hz, 0.6A, (ZVM-133-E)
95 watts (ZVM-133 and ZVM-133-E)
Characteristics

ZVM-135 Specifications
CRT .......................................... .
Pixel resolution ................................. .
Text capacity
................................... .
Video resolution
................................. .
RGB input ..................................... .
Composite input
................................. .
Synchronization
................................. .
Bandwidth
...................................... .
Rise time ...................................... .
Audio input ..................................... .
Audio output
................................... .
Height
......................................... .
Width
Depth
Weight ........................................ .
Power
......................................... .
13" diagonal, high-resolution color display
640 dots (RGB), 250 dots (composite)
25 lines of 80 characters (RGB)
25 lines
of 40 characters (composite)
640 pixels hOrizontal, by 240 lines (non-interlaced), or by
480 lines (interlaced)
5 volts positive polarity digital signal
NTSC 1 volt unterminated, or 75 ohm
terminated
± 1 volt to 5 volts horizontal
± 1 volt to 5 volts vertical
RGB: 20 MHz
Composite: 3 MHz
RGB: 70 nanoseconds
Composite: 100 nanoseconds
0.35 to 3.5 Vrms, 50
Kil, AC coupled
wired directy to Audio Input
13.75" (350 mm)
15.25" (390 mm)
15.25" (390 mm)
38 pounds (17.2 kg)
120YAC, 60 Hz, 1.23A, (ZVM-135)
240 VAC,
50 Hz, 0.6A, (ZVM-135-E)
95 watts (ZVM-135 and ZVM-135-E)
ZVM-136 Specifications
The ZVM-136 specifications are the same as ZVM-133
specifications except that the ZVM-136 has a high persis-
tance CRT.
Characteristics
Zenith Data Systems reserves the right to discontinue
products and to change specifications at any time.
Page 9

Installation
ZVM-131 and ZVM-135 Installation
COMPOSITE SIGNAL
1. Connect applicable cables as shown in Figure 2.
NOTE: A weak composite signal may not produce suffi-
cient contrast and brightness. Connecting the composite
signal to the VIDEO OUT connector will provide higher
gain for more contrast and brightness.
2. Set the RGB/COMP switch to COMPo
3. Select green or color:
If the monitor is to
be used for text display,
select green with the GREENIWHITE switch.
If the monitor is to
be used for graphics display
or combined text
and graphics display, select
color by switching the GREENIWHITE switch to
WHITE.
4. Perform the following adjustments for a color display
when using a composite signal
from a signal source
such
as a video cassette recorder.
a. Turn the COLOR LEVEL control all the way
counterclockwise to change the color display to
black-and-white.
b. Turn the DISPLAY DRIVE control to the mid-
range position.
c. Turn the BLACK LEVEL control to the midrange
(detent) position. This will cause the area of the
display intended to
be black, to become black.
d. Adjust the COLOR LEVEL control to give the
desired amount of color to the display.
e. Adjust the TINT control for the most pleasing
colors.
f. Adjust the DISPLAY DRIVE control for the de-
sired brightness level.
g. If the dark areas, color areas, or both, appear
faded or washed out, turn the
BLACK LEVEL
Page 10
control counterclockwise. If the light back-
grounds and colors appear too dark,
turn the
BLACK LEVEL control clockwise.
h. Set the SHARPNESS control for the preferred
sharpness.
RGB SIGNAL
1. Connect applicable cables as shown in Figure 2.
2. Set the RGB/COMP switch to RGB.
3. Select green or color:
If
the monitor is to be used for text display,
select green with the GREENIWHITE switch.
If the monitor
is to be used for graphics display
or combined text and graphics display, select
color by switching the GREENIWHITE switch to
WHITE.
4. Perform the following adjustments for a color display
when using an RGB signal. You will need a color bar
chart which can
be generated from the ROM in a Z-
100 or Z-100 PC Series Computer, or by using the
customer demonstration disk in a
Z- 100 PC. (See
the Servicing section.)
a. Turn the DISPLAY DRIVE control to the mid-
range position.
b. Turn the BLACK LEVEL control to the midrange
(detent)
pOSition. This will cause the areas of the
display intended to be black, to become black.
c. Adjust the DISPLAY DRIVE control to the de-
sired brightness level.
d. If the dark areas, color areas, or both, appear
faded or washed out, turn the BLACK LEVEL
control counterclockwise. If the light back-
grounds or colors appear too dark, tum the
BLACK LEVEL control clockwise.

AUDIO AMPLIFIER
OR RECORDER
;..
FROM COMPUTER
OR OTHER
AUDIO SOURCE
Installation
Figure 2
ZVM-131 and ZVM-135
Controls and Connectors
FOCUS
Page 11

~~-~!II
~
--I
I
Page 12
CONTRAST CONTROL
-GREEN-WHITE SWITCH
POWER INDICATOR
\
I
~
""'"""
........
i~
8
~
~tll
I
\
POWER SWITCH
-
rR'GBl
~
Z-100 LOW PROFILE COMPUTER
Figure 3
ZVM-133 and ZVM-136
Controls and Connectors
ill j
Installation

ZVM-133 and ZVM-136 Installation
1. Connect the cables as shown in Figure 3.
2. Select green or color:
If the monitor
is to be used for text display,
select green
by pushing the CONTRAST-
GREENIWHITE control.
If the monitor
is to be used for graphics display
or combined text and graphics display, select
color
by pulling out on theCONTRAST-GREENI
WHITE control.
Installation
3. Turn on the computer and monitor power switches.
The power indicator on the front of the monitor
should light.
4. After the monitor has warmed up, adjust the
BRIGHTNESS control for the desired display bright-
ness.
5. If the monitor is to be used with a personal com-
puter, display the
PC color bar from the ROM and
adjust the CONTRAST-GREENIWHITE control so
that the bottom eight color bars have the desired
color intensity.
Page 13

Circuit Descriptions
Refer to the block diagram, schematics, and waveforms in
the Servicing section.
ZVM-131 and ZVM-135 Circuit Boards
Refer to the block diagram in Figure B.
MAIN BOARD
The main board generates start-up and operating voltages
for itself and for other boards. Also, the RGB drive and
cutoff voltages and the horizontal and vertical drive volt-
ages are generated by the main board. See the following
detailed description.
Start-Up and Operating Voltages
Une voltage is supplied to the main board through connec-
tor
3RB. The AC voltage is then routed through fuse
FX3201 and a LCI (line conducted interference) choke.
The LCI choke, in conjunction with capaCitors CX3250 and
CX325B are to prevent noise generated within the monitor
from being fed back into the AC line. The power switch is
located across pins 2 and 3 of connector 38B.
Degaussing Circuit
Since externally generated magnetic fields can cause the
mask inside the CRT to become magnetized, the CRT is
automatically degaussed each time the monitor is turned
on.
Degaussing is accomplished by passing AC current
through the degaussing coil wrapped around the CRT. The
average value of the AC current is zero and therefore does
not allow residual magnetism to remain on the mask of the
CRT.
The degaussing coil is connected to the main board by
connector 3T8. A positive temperature coefficient thermis-
Page 14
tor (R3245) controls AC current flow through the degaus-
sing coil. When monitor power is turned on, a high AC cur-
rent will flow from one side of the AC line through the de-
gaussing coil, diode CR3210 or CR3211, and through ther-
mistor R3245 to the other side of the AC line. This high
AC current demagnetizes the mask and then quickly drops
to a value of near zero due to the heating and subsequent
high resistance of R3245.
Power Supplies
When the power switch is closed, AC voltage is applied to
the main board. The AC voltage goes to a simple bridge
rectifier comprised of diodes CR3231-CR3234. The output
of this bridge rectifier circuit acts as a source for some of
the other power supplies.
WARNING: The bridge rectifier circuit is referenced to hot
(AC) ground and is considered the hot part of the chassis.
Therefore,
an isolation transformer should always be used
whenever the monitor is serviced to prevent injury and
damage to the monitor and/or test equipment.
+150 VDC Supply
When monitor power is first turned on, the first power sup,
ply to develop output voltage is the +150 VDC supply.
This is the B+ power for the H.D.T. (horizontal output
transistor) located
on the high voltage and horizontal
sweep circuit board.
Several oscillators must be operating before additional
power supplies will work. For example, the horizontal oscil-
lator must be operating and driving the H.D.T. before high
voltage can be generated.

+26 VDC Supply
Transformer T3201 located on the main board is used as
a start-up transformer to provide the necessary voltage to
get the horizontal oscillator operating. AC current from the
secondary winding of T3201 is rectified by diode CR3224.
Only the positive alternations through CR3224 produce
voltage
as the negative alternations are shunted to ground
by CR3219. This half wave rectifier circuit supplies +26
VDC to the sync processor IC3401. An oscillator within the
sync processor then begins to operate, sending the hori-
zontal drive signal to pin 5 of IC3401.
+12 VDC Supply
The regulated + 12 VDC supply is derived from the +26
VDC supply and is used to power most of the transistors
found on the main board. Transistor 03200 is the active
regulator whose emitter supplies 12.7 VDC. Current flow
through CR3205 produces a proportional voltage drop
across the voltage divider comprised of resistors R3203
and R3202. The base of transistor 03201 is connected to
the middle of the voltage divider and therefore detects
changes in output voltage at the emitter of 03200. If the
output voltage decreases, the current through R3203
and
R3202 decreases and therefore the voltage at the base of
03201 decreases. When this occurs, conduction through
03201 decreases effectively raising the voltage at the
base of 03200. Regulator 03200 is driven harder, thereby
increasing its output voltage
and current-delivering capabil-
ity.
If the output voltage rises above + 12 VDC, the current
through resistors R3203 and R3202 increases and causes
the voltage at the base of 03201 to increase. This transis-
tor
is forced to conduct harder which lowers the voltage at
the base of 03200, and therefore its output voltage at the
emitter.
RGB Drive and Cutoff Voltages
The RGB signals are processed by the RGB gain control
board and are then interfaced to the main board through
connector
E.
Circuit Descriptions
The RED signal is supplied to the base circuit of emitter
follower transistor 02501. During its quiescent state, the
base of 02501 is biased to approximately 11.3 volts as de-
termined by
the voltage divider comprised of resistors
R2501 and R2502.
When an active-low RED signal drives the base of 02501,
the emitter of 02501 reproduces the signal and drives the
base of 02502 through potentiometer R2506. This poten-
tiometer establishes the bias voltage at the base of 02502
and therefore is used to vary the RED signal drive. The
RED signal cutoff voltage is adjusted by potentiometer
R2505 which is located in the emitter circuit of 02502.
The collector of 02502 conducts the inverted RED signal
to the base of emitter follower transistor 02507 which
drives the signal through resistor R2550 to pin 4 of con-
nector A.
The BLUE and GREEN signal drive circuits function in
exactly the same way as the RED signal circuits.
Composite Drive
The composite signal at pin 2 of connector C goes to the
base of emmitter follower transistor 03404. Capacitor
C3462, in conjunction with zener diode CR3409, protects
the base of 03404 from over-voltage conditions. Resistors
R3467, R3468, and R3470 determine the bias voltage on
the base. The composite signal goes from the emitter of
03404
to pin 27 of the sync processor (IC3401). Pin 16
of the sync processor drives the resulting signal to the
base circuit of 03405. The collector of 03405 supplies
each of the drive level adjustment potentiometers with the
signal.
Composite Vertical Sync
The sync processor adjusts the vertical signal with respect
to the horizontal signal, to provide properly synchronized
CRT scan.
If either positive or negative vertical sync is configured, the
Signal is supplied from pin 2 of connector E to the base
of common emitter transistor 03401. The inverted signal at
the base of 03401 goes to the base of common emitter
03402 and is then applied to pin 28 of the sync processor.
Page 15

Composite Horizontal Sync
The sync processor adjusts the horizontal signal with re-
spect to the vertical signal to provide a properly syn-
chronized CRT scan.
If either positive or negative horizontal sync is configured,
the signal is supplied from pin 1 of connector E to the
base of common emitter transistor 03403. The inverted
signal at the collector of 03403 goes to the base of emitter
follower 03404. The signal is then supplied to pin
27 of
sync processor IC3401 .
Horizontal and Vertical Drive Outputs
The sync processor, IC3401, contains horizontal oscil-
lators, horizontal automatic phase control (APC), horizontal
output driver, vertical oscillator, and vertical output driver.
The vertical output of IC3401 (pin 14) drives a stacked pair
of transistors (02101 and 02102) for vertical scan genera-
tion. This vertical output goes to connector 3G3 to supply
the sweep assembly.
The horizontal drive output of IC3401 (pin 5) also is routed
through connector 3G3 to the sweep assembly where it
will drive the H.D.T.
AUDIONIDEO SYNC BOARD
The composite video signal is supplied at the rear of the
monitor to either the video input connector or to pin 20 of
OB-25 connector. This signal is processed in IC1301 and
supplied to the main board at connector E after passing
through the GREENIWHITE switch.
The RGB and intensity signals are supplied at OB-25 con-
nector. The audio/video sync board processes various
forms of signals including Apple 4-bit matrix, PC intensity
function, and RGB from a Z-100 computer.
Synchronization (sync) signals
of positive or negative po-
larity, including composite, are supplied at OB-25 connec-
tor, processed at transistors 01723 and 01726, and sup-
plied to the main board at connector o.
The audio signal is supplied to either connector 9E4 or at
pin 18 of OB-25 connector. The signal is converted from
digital to analog
in IC1451 and then goes to the speaker
through capacitor C1451.
Page 16
HIGH VOLTAGE AND HORIZONTAL SWEEP
BOARD
This board will be referred to as the sweep board in the
following text. The horizontal drive signal originates in the
main board, enters the sweep board at connector 3G3,
goes to forward driver transistor 03206 and reverse driver
transistor 03209, and then to transformer T3205. The out-
put of T3205 goes to the H.D.T. through connector 3R3
with the H.D.T. output going to the sweep board through
the same 3R3. From connector 3R3, the H.D.T. output
goes to the width step board through connector 3S3. The
H.D.T. output also goes to the horizontal output trans-
former TX3204 where the following voltages are gener-
ated; CRT filament, CRT high voltage, Focus, G2, 170
Vpp, 60 Vpp, and Video B+.
The vertical output, which originates in the main board,
goes to the yoke through the sweep board after passing
through connectors 3G3 and 2A3.
WIDTH STEP BOARD
The horizontal sweep goes to the width step board before
reaching the horizontal windings of the yoke. Coarse width
selection is made at this board by the placement of P1 and
P2 jumpers as explained in Alignment and Adjustment in
the Servicing section.
VIDEO OUTPUT BOARD
All outputs of this board go to the CRT socket which is on
this board.
The REO, GREEN, and BLUE signals from the main board
enter at connector 5A2 and go to transistors 05102,
Q5103, and 05101 to drive the CRT.
The following voltages are supplied by the sweep board:
•
•
•
The CRT filament voltage
G2 voltage to connector 5X3
Focus voltage through a pigtail connector to the CRT
The +120 VOC transistor supply voltage along with G1
and BASE voltage are supplied to the video output board
by the main board.
Circuit Descriptions

ZVM-133 and ZVM-136 Circuit Boards
Refer to the block diagram in Figure 9.
RGB GAIN CONTROL BOARD
The RGB digital signals enter the monitor at input connec-
tor DB- 25 and then go to the RGB gain control board con-
nector SA7. The intensity (I) signal also goes to connector
SA7 if a PC- compatible computer is used.
RGB Signal Input
The RGB signals are then applied to hex buffer/driver
IC1700. When either the RED or GREEN signals are ac-
tive (low), they are outputed at pins 2 and 4, respectively,
to the bases of common collector transistors 01703, and
01704. Base current drive for transistor 01703 (RED) is
derived from the +12 VDC supply, through resistor
R1712, diode CR1704, and buffer IC1700. Similarly, base
drive for 01704 (GREEN) is derived through resistor
R1712, diode CR1703, and buffer IC1700.
When the BLUE signal is active, the base of common
emitter transistor 01709 is driven through resistor
R1711,
causing the transistor to conduct from emitter to collector.
When this occurs, the +12 VDC supply is loaded, and
therefore reduces the RED and GREEN signal current
drive capability. The gain on each respective signal is
Circuit Descriptions
therefore equal to each other. The BLUE signal drives the
base of 01705 through pin 6 of buffer IC1700.
RGBllnput
The intensity bit is used to enhance the hue of a particular
color by providing additional drive to the displayed color.
The displayed color is therefore intensified on the face of
the CRT and takes on a different hue. In this manner, as
many as 16 different colors can be displayed when using
a
PC.
The intensity bit is applied to pins 1 and 3 of hex buffer/in-
verter IC1700. When these signals are active, they force
the output at pins S, 10, and 12 of IC1700 low. This 3-bit
combination of data goes through diodes CR1707,
CR170S, and CR1709 to D/A converter IC1723. The D/A
converter processes the data and provides additional drive
voltage at pins S (RED), 2 (GREEN), and 5 (BLUE). This
voltage increases the bias on the bases of common collec-
tor transistors 01706 (RED), 01707 (GREEN), and 0170S
(BLUE). These RGB output transistors are therefore able
to provide higher level· RGB signals at their emitters. The
signals go to the main board through connector E.
See ZVM-131 and ZVM-135 Circuit Boards for the descrip-
tion of other ZVM-133 and ZVM-136 circuit boards.
Page 17

Servicing
Safety and Service Guidelines
WARNING: No work should be attempted on any part of
the chassis by anyone not familiar with Zenith service pro-
cedures and precautions; otherwise, personal injury may
result.
WARNING: With the monitor power turned off and discon-
nected, discharge the high voltage anode lead at the CRT
using a jumper lead connected between the chassis and
a screwdriver (see Figure 32). Failure to comply could re-
sult in severe shock and/or personal injury.
WARNING:
Do not operate the monitor with excessive
high voltage any longer than necessary or the monitor may
produce X-rays from the CRT.
Excessive high voltage will produce X-rays from the CRT;
always verify that the voltage is at normal levels when ser-
vicing the monitor.
WARNING: Carefully handle the cathode-ray tube when
you hold, remove, or install it; otherwise, implosion and/or
injury may result.
NOTE: Under no circumstances should the original design
be modified or altered without permiSSion from Zenith Elec-
tronics Corporation.
AC Leakage Test
To prevent electrical shock after reassembly, perform an
AC leakage test on all exposed metal parts of the monitor.
Do not use an isolation transformer to perform this test.
1. Connect the test circuit as shown in Figure 4.
2. With the monitor turned on, measure the leakage
voltage between earth ground and an exposed moni-
tor metal part.
3. Repeat the measurement with the meter leads re-
versed.
4. Repeat steps 2 and 3 until all exposeq metal parts
are verified to have satisfactory
AC leakage levels.
WARNING: Any leakage voltage measurement that ex-
ceeds 0.75 volts rms (0.5 milliamperes AC) constitutes a
potential shock hazard
and must be corrected.
CAUTION: Some of the ICs (integrated circuits) used in
the monitor are electrostatic-sensitive devices (ESO).
These circuits can be damaged by static electricity. When
handling any IC, use a wrist grounding strap or be sure to
equalize the static charge before touching the
IC.
A.C. VOLTMETER
(5KOHM/VOL T MINIMUM)
Page 18
ICLI
HE- 22-4384
.15jJF
A.C. TYPE
HE-
TO GOOD EARTH GROUND 63-10401-76
SUCH AS WATER PIPE,
CONDUIT, ETC.
1500n
10 WATT
PLACE THIS PROBE
ON EACH EXPOSED
METALLIC PART.
Figure 4
AC Leakage Voltmeter Circuit

•
•
•
Other Precautions
Be sure that all components are positioned in such
a manner as to avoid the possibility of short circuits.
Inspect and correct all soldered connections for cold
solder joints, frayed leads, damaged insulation,
splashed solder, or sharp points.
Never release a repaired product to a customer un-
less all protective devices, such as insulators, bar-
riers, cover shields, strain reliefs, etc., have been in-
stalled.
• Remove all loose material from inside the monitor
after servicing.
•
•
Follow the original lead layout, dress, lengths, and
tension.
Replace all components with exact Zenith replace-
ment parts.
Suggested Tools and Supplies
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
1/4-inch nut driver
Flat-bladed screwdriver, 1/4-inch blade
Phillips screwdriver, No.1 tip
Phillips screwdriver,
No.2 tip
Diagonal cutters
Wire strippers
Long-nose pliers
Desoldering tool
Soldering iron, 25 to 40 watts
Solder, 60/40, HE-331-59
Desoldering braid, HE-490-185
Cable ties, HE-354-59
Lint-free cloths
Test Equipment
Oscilloscope - DC to 100 MHz, dual trace, triggered
sweep. Tektronics Model 465, or equivalent.
Logic probe -Capable of detecting 10 nanoseconds
single pulses, and indicating logic one, logic zero,
and high impedance states. Heath Model IT-741 0, or
equivalent.
Servicing
•
•
•
•
Digital voltmeter -High impedance input, zero to
1000 volts, zero to one megohm. Heath Model SM-
2215, or equivalent.
Variable power supply -Zero to 120 VAC rms, 3
amps Heath Model IM-5210, or equivalent.
Low capacitance oscilloscope probe -Input capaci-
tance adjustable from 15 pF to 50 pF, 4 ns rise time.
Heath Model PKW-105, or equivalent.
High voltage probe -Zero to 40
kV. Heath Model
IM-5210, or equivalent.
• Isolation transformer
Troubleshooting
Use the following inspection to determine possible causes
of monitor failures.
• Verify proper computer operation.
•
•
•
•
•
•
•
•
•
Check monitor controls.for proper response and set-
tings.
Unplug the signal and power cables from the monitor
and check for burnt insulation,. broken wires, or loose
prongs
on plugs.
Check the AC receptacle (wall outlet) for proper sup-
ply voltage.
Check all cabling and internal circuit board plugs for
proper electrical connections. Refer to the applicable
block diagram and component location illustrations
for cable connector asSignments.
Check monitor adjustments as explained at the end
of this section.
Check all circuit boards for broken or burnt compo-
nents or for darkened areas or other signs of compo-·
nent overheating.
Verify that the GREENIWHITE switch is
in the cor-
rect position.
When power is applied, check the CRT for glowing
filament.
When power is applied, check for high voltage by
placing the back of the hand near the face of the
CRT.
Page 19

Table 1
General Troubleshooting
PROBLEM POSSIBLE CAUSE
Dead monitor
No power at source
Power cord
Fuse
Connector 3R8
Connector 3S8
Power switch
No display
RGBcable
95 volt supply
No color
GREENIWHITE switch
Software
produces monoc-
hrome display
Green color only
GREENIWHITE switch
Software produces green dis-
play
Out of focus
Focus control
Raster displayed
G2 control
Display does not fit
P1, P2 on the sweep board
on CRT
Width control
95 volt adjustment
Fault Isolation Procedures
Have the monitor sync-locked to a signal, if possible, be-
fore starting this procedure.
Always reference the DVM
or oscilloscope to DC (cold)
ground unless instructed otherwise.
A 10X probe is recommended for use with the oscillo-
scope.
1. With a DVM, measure the voltage at pin 2 of con-
nector 3V3 on the main board (see Figure 16).
If +150 VDC is present, proceed to step
2.
If +150 VDC is not present, replace the main board.
Page 20
2.
3.
4.
With a DVM, measure the voltage at pin 2 of con-
nector 3F3 on the main board.
If the voltage is from +4.5 VDC to +12 VDC, pro-
ceed to step 3.
If the voltage is less than +4.5 VDC, replace the
main board.
With a DVM, measure the voltage at pin 2 of con-
nector
303 on the main board.
If the voltage is from +12 VDC to +26 VDC, pro-
ceed to step 4.
If the voltage is more than +26 volts, replace the
main board.
With a DVM, measure the voltage at pin 2 of con-
nector 3G3 on the main board. A value of +0.3 VDC
should be observed. Observe this point with an oscil-
loscope and verify the presence of horizontal drive
pulses.
If the pulses are present, proceed to step
5.
If the pulses are not present, replace the main board.
5. With an oscilloscope, measure the supply voltages at
connector 303 on the main board. The voltages
should be:
Pin 1 170 volts peak to peak
Pin 2 +26 volts DC
Pin 3 Ground
Pin 5 60 volts peak to peak
Pin 6 140 volts peak to peak
If all voltages are correct, proceed to step 6.
If any voltage is not correct, replace the sweep as-
sembly.
6. Use a high voltage probe to verify the presence of
26 kV on the CRT anode lead.
If +26 kV is present, proceed to step
7.
If +26 kV is not present, replace the sweep assem-
bly.
Servicing