Goldstar MBM-2105 G, MBM-2105 A Service Manual
GolclStar
MONOCHROME MONITOR
SERVICE MANUAL
WTION
BEFORE SERVICING THE CHASSIS, READ THE “SAFETY
PREtXJTK)NS”, IN THIS MANUAL
MODEL:
MBM-2105GIA (MC-3 CHA=W
B GoldStar
FEATURES
l 2000 display characters in a 8 x 8 dot format.
l 18 MHz bandwidth, medium class, composite signal input.
l This monitor is compatible with a variety of home and personal computers
CONTROLS LOCATION
The MBM-2105GIA monochrome monitor uses a RCA jack connector.
The input signal is input through the RCA jack connector.
The input signal is based on the composite level.
Figure 2 shows the monitor controls on the front and rear panels.
\
r---
--
[
/
t
yLcPower
Indicator
H-Size
Video In
Contrast Brightness Power H-Position H-Hold V-Sue Power Cord
0
POWER (PUSH-ON)
Turn on the monitor by pressing the power switch.
The power indicator lights when the power is ON.
Always turn on the monitor before you turn on the
computer.
To turn the power OFF, just press this switch again.
0
Brightness
Turn this knob clockwise to increase brightness.
0
Contrast
Turn this knob
0
V-Size
Turn this knob to adjust the vertical size of the
picture.
clockvvise
I
Figure 2, Monitor Controls
NOTE: Monitor cabinet not used on 6300T Models.
to increase contrast.
0
H-Hold
Turn this knob to stop horizontal rolling of the
picture.
0
H-Position
Turn this knob clockwise to move the center of the
picture to the right; turn the knob counterclockwise
to move the center of the picture to the left.
0 H-Size
Turn this knob to adjust the horizontal size of the
picture.
CIRCUIT DESCRIPTION
1. VIDEO AMPLIFIER 2. POWER SUPPLY
The Fig. 3 details the cascade video amplifier.
Video amplification is provided by the TR303 and
TR304. TR303 and TR304 are connected in a
cascade configuration. TR303 operates as a
common emitter and TR304 operates in the
common base configuration. This minimized the
miller effect input capacitance and the difining
breakdown parameter for TR303 which becomes
BVCBO as opposed to BVCEO.
This enables selection of a higher speed/lower
breakdown transistor to be used in the video
amplifier.
The emitter of TR304 is driven by the collector of
TR303 which is a high frequency transistor.
Overall voltage gain for the stage is determined
by the ratio of R312 to R316. Bandwidth is within
3dB to 32 MHz.
The 120V AC line voltage is applied to the primary
of the T901 where it is stepped down through the
secondary winding to approximately 17V (AC).
After passing through the bridge rectifier circuit
and filter (C905) the regulated DC supply voltage
is approximately 18V (DC). The 18V unregulated
B+ voltage is applied directly to the collector of the
B+ regulator (TR901). A voltage divider network
(R905, VR901, R906) in which the B+ adjustment
control (VR901) is used to establish the desired
operating level (12V DC). When AC input voltage
variations occur, a correction voltage is produced
at the base of TR903 and is coupled directly to the
base of the error amplifier (TR902). This correction
voltage is then passed from the emitter of TR902
directly to the base of TR901 and B+ voltage
regulation is then accomplished.
TO@
c305
lOOuF/
TO
@
<
‘16V
R316
1
.ZK/ZW
TR304
3
KTC2229
R317
330
TR303
2N3904
C306
12OP
R313
47
R314
;
+
R309
75
L301
4.7uH
7
l
+
2~ C308
2.2uFll
l
TO
v
0
oov
TO
CRT CA.THODE
Figure 3, Video Ampllfler
Vertical
Oscillator
F,B)
vcc 2
Vetical Frame
Vcc 2 Generator
1
Oscillator
Frame-Synchro
Figure 4, BLOCK DIAGRAM OF THE TEA 2037A
1
Line Fly Back Phase
Input Detector
3. COMPOSITE VIDEO INPUT AND HORIZONTAL/
VERTICAL DEFLECTION
3-l VIDEO INPUT (PIN 15) 3-3
The detection level for negative sync pulse at the
sync separation input (pin 15) is set at 1.6V. When
the voltage at emitter of the Transistor (pin 15) is
above
1.6V, the transistor is cut off. Voltage
lower than 1.6V enables the transistor to conduct
and the internal circuitry
is
enabled for
synchronization function.
Generator
Vertical
output
Power
Amplifier
Input
Horizontal
output
Horizontal
Oscillator
LINE (H) OSCILLATOR (PIN 9)
The line oscillator is of the type which charges and
discharges a capacitor, since a perfectly linear
sawtooth wave form is not required.
The free running frequency is dependent on C705,
R705 and VR702 and is governed by this expression To = 085 x C705 x R705 where To is the line
oscillator free running frequency.
3-2 COMPOSITE VIDEO INPUT (PIN 15)
3-4
FRAME(V) OSCILLATOR (PIN 9)
Oscillator thresholds are internally fixed by
resistor C601, R603 are used to determine the
free-running frequency, the oscillator
free-running frequency is given by To = 0.15 x
C601 x R603.
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