Goldstar Mbm 2105 Monochrome Service Manual

							GolclStarMONOCHROME MONITOR
SERVICE MANUAL
WTIONBEFORE SERVICING THE CHASSIS, READ THE “SAFETYPREtXJTK)NS”, IN THIS MANUALMODEL: 
MBM-2105GIA (MC-3 CHA=W
B GoldStar 
						

							FEATURESl 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 LOCATIONThe 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-SizeVideo InI
ContrastBrightness PowerH-Position H-Hold V-Sue Power Cord
Figure 2, Monitor ControlsNOTE: Monitor cabinet not used on 6300T Models.
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 
clockvvise to increase contrast.0 
V-SizeTurn this knob to adjust the vertical size of the
picture.
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-SizeTurn this knob to adjust the horizontal size of the
picture. 
						

							CIRCUIT DESCRIPTION1. VIDEO AMPLIFIER2. 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 withinThe 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. 3dB to 32 MHz.
TO@c305lOOuF/
TO 
@
R316L301
1 .ZK/ZW4.7uH
7l TO
+
TR3042~ C308
R314KTC22292.2uFll
< ;
+l TO
‘16VR317
330
3
TR303
2N3904
C306
12OP R309
75
R313
47
0v
oovCRT CA.THODE
Figure 3, Video Ampllfler 
						

							Vertical
OscillatorF,B)vcc 2Vetical Frame
Vcc 2 Generator
1 Oscillator 1Frame-SynchroGenerator
Line Fly Back Phase
InputDetectorHorizontal
OscillatorVertical
output
PowerAmplifier
Input
Horizontal
output
Figure 4, BLOCK DIAGRAM OF THE TEA 2037A
3. COMPOSITE VIDEO INPUT AND HORIZONTAL/
VERTICAL DEFLECTION3-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
above1.6V, the transistor is cut off. Voltage
lower than 1.6V enables the transistor to conduct
and theinternalcircuitry
isenabled for
synchronization function.
3-4
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 expres-
sion To = 085 x C705 x R705 where To is the line
oscillator free running frequency.
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 xC601 x R603.
3-2 COMPOSITE VIDEO INPUT (PIN 15) 
						

							ADJUSTMENT1. REGULATED B + ADJUSTMENT 
(VRSOl)Connect high impedance voltmeter between
TR901 emitter and ground rotate the B +
adjustment control 
(VR901) to obtain a reading of
12.0 2 
O.lV.2. FOCUS 
(VR704)Adjust the focus control (VR704) for best overall
focus of the test pattern (marked with the symbol“%“). Usually the center and corners of the
screen do not focus at the same setting and a
compromise must be made.
3. VERTICAL 
SIZE (VR601)The vertical size control (VR601) should be adjust
for the picture to fill the screen vertically.
4. HORIZONTAL SIZE 
(L703)The horizontal size control (H-site coil) should be
adjusted for the picture to fill the screen horizontal-
ly.
5. HORIZONTAL POSITION NR701)The horizontal position control (VH701) snould be
adjusted for the horizontal picture position.
6. SUB-BRIGHT (VR703)
Adjust subbright control (VR703) for 
visual cut off
of the raster when external brightness is turned to
maximum
7. CENTERING ADJUSTMENTIt the raster is not centered horizontally and verti-
cally it may be centered by removing the cabinet
back and adjusting the centering tabs on the neck
of the tube, located at the rear of the deflection
yoke. Turn the whole device clockwise or
counterclockwise. To increase the amount of raster
shift move the two tabs which project from the
device farther apart, if raster is tilted on an angle,
it may be straightened by loosening the deflection
yoke clamp and rotating the deflection yoke.
BLOCK DIAGRAMV,deo Input
0Video Preamphf~erTR301. TR302Video Output
TR303, TR304
TEA 2037A
AC 
12OVLllWPOW&YPW+.?r
REG., +12v60HzFilterTMlS 
						

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MnJ%- 4thH.HOLD uR705
VR70233Kb.lK12Ul
INOTES: 1. RESISTORS ARE SHOWN IN OHMS
K 
= 1.000M = 1.000.0002. CAPACITORS ARE SHOWN
IN 
UF OTHERWISE NOTED P : cc Ir
3. All RESISTORS ARE 
f 5%TOLERANCE UNLESS OTHERWISE NOTED
u u4 ItlPORTANT SAFETY NOTICE bTHE 
SYMBOL MARK OF THIS SCHEHATIC DIAGRAM INCOIFEATURES IMPORTANT FOR PROTECTION FROM X-RADIA
ELECTRICAL SHOCK HAZARDS. WHEN SERVICING IT IS
ONLY MANUFACTURER’S SPECIFIED PARTS BE USED 
FCOl’lPONENTS IN 
THE&YUBOL MARK OF THE SCHE
AIBIC 
						

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DIEFG 
						

							TROUBLESHOOTING GUIDETR902, TR903. D905.TR901 AND POWER
REG CIRCUIT~.7
ID706, 
c713. c714. c715YES
, CHECK CRT (GZ) VOLTAGE 450VNOTROUBLE IN
2 CHECK CRT (HEATER) VOLTAGE 12V
-, FBT. CR706 R712
LEAD (HI,. LEAD (Vl, V2)
YES
CHECK CRT CATHOD VOLTAGEABOVE 55VTROUBLE IN
*45-55vTR303, TR304. R311. R309. R310.R315, R314, R312
YESVR703 (SUB-BRIGHT,, R710. R711. 
“R301 (CONTRAST,,VI?,05 (MT BRIGHT,, TRW, TR302. VIDEO CABLEHORIZONTAWERTICAL
SYNC TROUBLEISYNCTROUBLE
TROUBLE INR719. C716. R70B, R720.
I
IREF. NO.FIGUREOEBCRIPTIONTR301. TR302.
B
wKTC ,015
TR902,KTC 1959TR903.-CKTA 562TMTR601KTC 1815LTR304
kKTC 2229t Bc
>TR701.
9BU 806TWO1KTD 880BCEIC701
l@aTEA 2037A
TR303
-02N 3904E 
						

							PRINTED CIRCUIT BOARD
1. MAIN PCBASSY PIN: 1 lo-BOW
ASSY PIN: ilO-B72A
JGSEP-2112TIBLACK 
						

							3. MAIN PCB (SOLDER SIDE)
4. LINE FILTER PCB (SOLDER SIDE)
O-0
Lsol
I