Philips MG5.1E User manual

Published by LM 9972 Service PaCE Printed in the Netherlands Subject to modification 53122 785 10053
©
Copyright reserved 1999 Philips Consumer Electronics B.V. Eindhoven, The
Netherlands. All rights reserved. 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, or otherwise without the prior permission of Philips.
Colour Television Chassis
MG5.1E
AA
Contents Page
1 MG99 Light path 2
2 Introduction 8
3 Overall blockdiagram 9
4 Power supply 11
5 Scan circuits 24
6 Small signal panel 29
7 CRT drive circuit 69
8 Interface panel 72
9 SIDE JACK panel 74
10 Audio signal part 75
11 Digital convergence circuit 80

2 1. MG99 Light path MG5.1E
Personal notes
1. MG99 Light path
Figure 1-1
BLUE
GREEN
RED
MIRROR
FRESNAL
LENS LENTICULAR SCREEN
R+G+B
CL 96532100_078.eps
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The MG99 Projection TV uses three single color tubes, Red,
Green, and Blue. (Figure 1-1) The output of each tube is
projected onto a mirror where it is then reflected onto a viewing
screen. The Tubes are converged so the light from each tube
strikes the same spot on the Fresnel Lens. The Fresnel Lens
equalizes and concentrates the light to provide equal light
uniformity across the screen. The Mirror is a first surface mirror
type which has the reflective coating on the outside of the
mirror. To prevent scratching of this surface, always use a soft
cotton cloth to clean it.

MG5.1E 1. MG99 Light path 3
Personal notes
Figure 1-2
LIGHT
OUTPUT
BLACK STRIPING
CL 96532100_079.eps
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The Lenticular Lens Screen calumniates the light from the
Fresnel Lens. (Figure 1-2) The Lenticular Lens increases
contrast by reducing the ambient light by the use of Black
Striping. The Prismatic formation of the screen allows for nearly
3X light output as compared to a flat screen. Caution should be
used when working with the screen. Damage can easily occur
in the form of scratching, or by using certain chemical screen
cleaners which can strip the black striping from the screen. To
clean the screen, use one drop of dish washing detergent in a
small bowl of water. (approximately 2 liters) Wipe the screen
with a soft cotton cloth in the direction of the stripes.

4 1. MG99 Light path MG5.1E
Personal notes
Figure 1-3
CRT
C ELEMENT LENS
LIQUID COOLANTOUTPUT LENS
CL 96532100_080.eps
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The Three CRT's are driven by 30KV of high voltage and 15KV
of focus voltage. (Figure 1-3) The Tube produces a highly
concentrated light output of color. A liquid coolant of Glycol is
used to transfer heat from the face of the tube to the
surrounding mechanical assembly. The
C-element lens seals the Coupling fluid within the coupler. The
C-element lens and Coupling fluid are part of the light path and
contribute to the properties of the optical system.

MG5.1E 1. MG99 Light path 5
1.1 MG99 LIGHT PATH PROBLEMS
Personal notes
1.1 MG99 LIGHT PATH PROBLEMS
Figure 1-4
CL 96532100_107.eps
021299
Look at the edges of the screen. They may be bowed inward.
PROBLEM - BOTTOM CORNERS DARK
PROBLEM - BOTTOM CORNERS COLORED
There is no problem with the set. The viewing angle is too high.

6 1. MG99 Light path MG5.1E
1.1 MG99 LIGHT PATH PROBLEMS
Personal notes
Figure 1-5
CL 96532100_109.eps
151199
Fresnel may be reversed. Carefully remove the fresnel and
point the grooves toward the viewer.
PROBLEM - BRIGTH AND DARK LINES ON A WHITE FIELD

MG5.1E 1. MG99 Light path 7
1.1 MG99 LIGHT PATH PROBLEMS
Personal notes
Figure 1-6
CL 96532100_110.eps
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The Fresnel offset is pointing down. The center of the Fresnel
should be toward the top of the screen.
PROBLEM- UPPER CORNERS OF THE SCREEN DARK

8 2. Introduction MG5.1E
Personal notes
2. Introduction
The 1999 MG99 PTV chassis is designed for the European
market. It is available in a 46 inch (117 cm) and a 55 inch (140
cm) 16 by 9 aspect ratio screen sizes. Selected Video can be
displayed in either a 4 by 3, 14 by 9, or 16 by 9 aspect ratios.
The set has a viewing angle of 160 degrees.
The MG99 PTV is capable of receiving signal from PAL B/G,
PAL B/G 6OHz, PAL B/H, PAL D/K, PAL 1, PAL M, PAL N, PAL
plus, SECAM B/G, SECAM D/K, SECAM L, AND SECAM Li TV
systems. There are four composite video inputs which include
three SCART connectors, and a Side Jack panel. The systems
that can be applied to these inputs are NTSC 3.58, NTSC 4.43,
NTSC Play Back, PAL 4.43, PAL, B/G Play Back, SECAM, and
SECAM Play Back.
The set is equipped with a Frame and Line doubler to produce
a horizontal resolution greater than 800 lines. The picture
display is driven by three seven inch Red, Green, and Blue
tubes.
The Sound system is driven by a 2 times 20 watt power
amplifier. A switch in the rear of the set allows the sets internal
speakers to be driven by an external amplifier.
The following sets will be sold in Europe:
46PP9501/05U.K. and Ireland
55PP9501/05U.K. and Ireland
46PP9501/12Western Europe
55PP9501/12Western Europe
46PP9501/58Eastern Europe
55PP9501/58Eastern Europe
These units will be distributed from Philips Bundling Center in
Bruges, Belgium.

9 3. Overall blockdiagram MG5.1E
3. Overall blockdiagram
Figure 3-1
Y_CVBS
C
L
R
DELAY SVM
MODULE
CRT
DRIVE
CIRCUIT
GREEN
CRT RED
CRT
BLUE
CRT
Y
R
G
B
G
B
R
AUDIO
AMPLIFIER
LEFT AUDIO
RIGHT AUDIO
LINE
DRIVE
FRAME
DRIVE
HV
CIRCUIT FOCUS/G2
BLOCK
LINE SYNC
FRAME SYNC
CONVERGENCE
PANEL
INTENSITY
CONTROL
CONV R, G, B, FB
CONV R, G, B, FB
INTERFACE PANEL
HV/SCAN
PANEL
CONV
YOKES
SIDE JACK
PANEL
MG99 SMALL
SIGNAL PANEL
LINE SYNC
FRAME SYNC
+5V STBY
+15V STBY
+130V
+38V
-38V
+33V
+15V
-15V
-7V7
+8V6
+5V2
POWER
SUPPLY
AC
SWITCH
PANEL
SWITCH
SPEAKER
FOCUS
G2
CL 96532100_081.eps
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10 3. Overall blockdiagram MG5.1E
Personal notes
There are eleven PC boards in the MG99 chassis. (Figure 3-1)
They are the Small Signal panel, Side Jack panel, Power
Supply panel, Interface panel, SVM module, Blue CRT panel,
Green CRT panel, Red CRT panel, High Voltage Scan panel,
and Convergence panel.
Whenever AC power is applied to the set and the Mains switch
is turned On, the Power Supply panel produces a 5 and a 15
volt standby supplies. When the set is turned On by the channel
up button on the Front Keyboard or the Remote Control, the
130 volt, 38 volt, -38 volt, 33 volt, 15 volt, -15 volt, -7.7 volt, 8.6
volt, and 5.2 volt supplies are switched On.
Frame and Line drive from the Small Signal panel is routed
through the Interface Panel to the Frame Drive and Line Drive
circuits on the High voltage Scan panel. The High Voltage scan
panel produces the High Voltage and Sync to the Convergence
panel. Focus voltage from the High Voltage circuit is fed to a
Focus/G2 block which provides Focus and G2 voltage to the
three CRT'S. During the Convergence adjustment mode, Red,
Green, Blue, and Fast Blanking from the Convergence Panel is
fed to the Small Signal panel to generate the adjustment grid.
The Small Signal panel selects video from the Antenna input,
one of the three Scart connectors, or the Side Jack panel. The
Small Signal panel outputs Red, Green, and Blue drive to the
CRT drive circuit located on the Interface Panel. The CRT drive
circuit then provides drive for the three CRT panels.
Left and Right channel audio from the Small Signal panel is
routed through the Interface Panel to the Audio Amplifier panel.
The Audio Amplifier panel has its own separate Switch Mode
power supply. The output of the Audio Amplifier is then fed to
the Speaker Switch panel which selects between the Audio
Amplifier or External Audio from a separate amplifier.
Luminance or Y from the Small Signal panel is fed to a Delay
circuit on the Interface panel before being applied to the SVM
panel. The Scan Velocity Module speeds up the beam during
light to dark transitions in the picture to provide a sharper
image.

11 4. Power supply MG5.1E
Personal notes
4. Power su pply
Figure 4-1
AC
INPUT
CIRCUIT
AC
SWITCH
PANEL
POWER
FACTOR
CORRECTION
CIRCUIT
STBY
POWER
SUPPLY
MAIN
SMPS
POWER
SUPPLY
+5V STBY
+15V STBY
+130V
+33V
+35V
-35V
+15V
-15V
ON/OFF
+15V 5V2
REG +5V2
+15V 8V6
REG +8V6
-15V -7V7
REG -7V7
CL 96532100_082.eps
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AC power is applied to the set on the Power Supply panel.
(Figure 4-1) It is then fed to the Mains switch on the AC switch
panel located on the front of the set. It is then fed back to the
Power Supply panel and to the Power Factor Correction circuit.
If the AC mains is 240 volts, the output of the Power Factor
correction circuit is approximately 329 volts DC in standby and
350 volts DC when the set is turned On. The Power Factor
correction circuit is turned Off during standby. This is a "HOT"
chassis. When troubleshooting this or any power supply,
always use an isolation transformer.
The Standby Power supply produces a 5 and a 15 volt supplies.
It also provides operating voltage for the Power Factor
Correction and the Audio Amplifier power supply. The Power
Factor correction circuit is turned Off when the set is in the
Standby mode.
The Main Switch Mode Power supply produces a 130 volt, a 33
volt, a 35 volt, a -35 volt, a 15 volt, and a
-15 volt supply. The Main SMPS and the Power Factor
Correction Circuit is switched On by a Low from the Small
Signal panel.

MG5.1E 4. Power supply 12
Personal notes
Figure 4-2
3011
2000
680n
1000
5A 5001
1221
TO AC SW BD
14
3004
3.3M
3005
3.3M
3006
470K
7000
3007
6.8K
3008
10K
+5VSTBY
50_60HZ
CL 96532100_083.eps
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The applied AC voltage is fed to a 5 amp fuse and then to the
Mains switch on the AC switch panel. (Figure 4-2) The AC
voltage is fed to transistor 7000 and then to the Small Signal
panel for clock synchronization.
The Standby Supply produces the 5 volt and 15 volt standby
supplies. (Figure 4-3) The output of the Power Factor correction
circuit PFCOUT is applied to Pin 5 of 7211 through Pins 2 and
4 of the switching transformer 5202. When the supply voltage
is first applied, voltage through the internal startup resistor Rs
is applied to capacitor 2283 via Pin 4. When the capacitor
charges to 5.7 volts, the internal oscillator switches On driving
the internal FET switch. When the voltage across capacitor
2283 drops below 4.7 volts, the IC turns Off. This cycle repeats
until the 5 volt standby supply turns Shunt Regulator 6205 On.
The supply voltage for the IC is then supplied to Pin 4 through
7213. Operating voltage to Pin 5 of 7213, the Audio Amplifier
power supply, and the Power Factor correction circuit is
supplied by Pin 5 of 5202. During normal operation, the 5 volt
standby source is monitored by the Shunt Regulator 6205. If
the 5 volt supply should increase, the Shut Regulator will cause
more current to flow through the LED inside the opto-isolator
7213. This will reduce the resistance of the transistor inside
7213. As a result, more current will flow through the Sensing
resistor inside 7211, which will reduce the On time of the FET
inside the IC. This will reduce the output voltage to the correct
level. This supply operates at approximately 100 KHz.

MG5.1E 4. Power supply 13
Figure 4-3
RESET
7211
7213
1 2
4 5
3287 470
2283 47uF
+5VSTBY
3223 47
3244 33K
2206 220uF
2228 100
6207
6200 6236
5202
5
4
1,2,3,7,8
6235
2211 .1
3230 1K5
6201 8.2V
7209
2208 100 6231
6204 2269 100
2270 100uF
+15VSTBY
2213 1000uF
3239 2K4
2226 22n
6205 SHUT REGULATOR
3240 39K
2210 22uF
7208
5234
2282 1uF
RESET +5VSTBY SOURCE
3245 1K
3247 180
1
5 2 4
7
10 9 8
PWM
RS
5.7V 5.7V
4.7V
INTERNAL SUPPLY
-
RS
PFCOUT
3246 2K4
3222 1K5
ON_OFF
3289 10K
3288 10K 2284
10n
7214
+5VSTBY
3212 10K
3214 100K
7205
+5VSTBY
3215 1K
7206
3241 6K8
1
24
5
GND_C
3213 10K
7204
2209 100uF
5214
5211 5233 PFC
CONTROL
GND_C
GND_C
GND_C
GND_C
GND_C
3216 10
CL 96532100_084.eps
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14 4. Power supply MG5.1E
Personal notes
To troubleshoot the Standby Supply, first check the supply
voltage on Pin 5 of 7211. If there is no secondary voltage and
7211 is working correctly, startup pulses should be seen at Pin
5 of the IC. If the IC is pulsing and there is no secondary
voltage, there is a problem with the outputs of 5202 or with the
feedback circuit. If 7211 is not pulsing, either the IC or capacitor
2283 is defective.
When the set is turned On, transistor 7214 will turn Off turning
7205 On. This will turn the Optoisolator 7206 On turning
transistor 7204 On, switching the operating voltage to the
Power Factor Correction circuit. It also switches the operating
voltage to the power supply on the Audio Amplifier panel on the
line labeled "CONTROL".

MG5.1E 4. Power supply 15
4.1 European power factor correction circuit
Personal notes
4.1 E uropean power fac tor correction c ircuit
Figure 4-4
CAPACITOR
CHARGE
AC CURRENT
VOLTAGE
AC IN BRIDGE
CAP LOAD
AB CL 96532100_085.eps
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The input to most switching power supplies consists of a bridge
rectifier and a large electrolytic capacitor. (Figure 4-4) When
AC power is applied, the Capacitor will charge to approximately
1.4 times the RMS value of the applied AC voltage. This type of
supply does not draw current from the AC power source
through out the entire AC cycle. When the capacitor charge falls
to point "A", the instantaneous value of the AC voltage exceeds
the charge of the capacitor. The bridge diodes are then forward
biased, causing current to flow from the AC source. Current will
continue to flow from the AC line until the AC sinusoidal voltage
reaches its peak at Point "B". At this point, the charge on the
capacitor will exceed the AC line voltage reversing the bridge
diodes. This results in an AC current waveform that is narrow
and distorted compared to the AC voltage waveform. Non
sinusoidal waveforms have a high harmonic content, with
excessive peaks which results in a low power factor of 0.5 to
0.6. Power Factor is a ratio of real power divided by apparent
power. Excessive harmonics and peak currents reduce the
efficiency of the power distribution system.
The MG5.1 Projection TV without Power Factor correction has
a high harmonic content of 85 percent, creating a Power Factor
of 0.5. Current spikes of 7 amps will also be created in the AC
supply. With the Power Factor correction circuit, the peak
current is limited to 1.58 amps, with the harmonic content being
reduced to 4.5 percent. The Power Factor is increased to 0.99.
The ideal Power Factor is one, which occurs when the current
is sinusoidal and in phase with the voltage. The European
standard IEC1000 limits the current harmonic content of
equipment supplied by the AC Mains.

16 4. Power supply MG5.1E
4.1 European power factor correction circuit
Figure 4-5
REGULATOR
DRIVE
BRIDGE
7104
2110
AC INPUT 350V DC OUT
6103
5109
CURRENT SENSE
53
7102
CL 96532100_086.eps
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The MG5.1 Power Factor correction circuit uses a Boost
regulator to smooth out the current draw from the AC line
improving the Power Factor to 0.99, which is accomplished by
drawing current from the AC source throughout the entire AC
cycle making the current waveform sinusoidal. (figure 4-5) Input
to the module is connected to the AC Mains. The output
supplies are approximately 350 volts DC to the Main and
Standby Switched mode Power Supply circuit. The Boost
Regulator circuit produces a higher output voltage than the
input voltage. The regulator drive circuit compares 6103's
output voltage, the input voltage from the bridge, and the
voltage across the current sensing resistors to control the On
time of 7104. This will maintain the output voltage at 350 volts
DC and limit the input current to acceptable levels. When 7104
is On, current flow through 5109 stores energy in the choke.
When 7104 turns Off, 5109 reverses polarity and charges 2110.
Using this type of regulation, current is drawn from the AC
source throughout the entire cycle, keeping the current
waveform sinusoidal. When the AC cycle is at its low point,
7104 is on for a longer period of time. When the AC voltage is
at its peak, 7104 is on for a shorter time to store the same
amount of energy in 5109 to maintain the output voltage at 350
volts.
If the Boost regulator circuit should become inoperative, due to
a loss of regulator drive, operating voltage is still applied to the
set. The supply voltage to the switching supplies will drop from
350 volt to approximately 329 volts depending on the Mains
voltage. Since the customer would not detect a failure, the
operation of this circuit should be checked after any repair of
the set.

MG5.1E 4. Power supply 17
4.2 F ull power factor correction circuit
Figure 4-6
-
+
-
+
- +
-
+
5005
5003 5004
3010 2R2
6000
3130 0R1 3131
0R1 3132
0R1 3133
0R1
5109
3117 10K
7104
5107
5105 6103
2110 470uF
R493 33K C486
.22
R491 330K
C485 .22
3111 1M
R490 1M 3115
47
5108
3114 47 6104
20 15
1.28
V REF OVP
IPK
LATCH
S R
Q
OSCILLATOR
19
VCC
17 18
3109 47K 3110
39K
3108 3M3
11 3
2
3120 5K6
3118 390
2118 1uF
5
93127
18K
3128 1K8
2116 2n2
8
13
3124 330K 2115
.33
3123 1K8
14
GILBERTS MULTIPLIER
3119 3M3
3126 47K
3125
1K
4 7
6
5.11V
7102
16
3121 33K 2114
1n5
350V DC OUT
OUTPUT
LOGIC
COMPARATOR
CURRENT AMPLIFIER
5.11 V
35
15 13
5.11V
19V (25V)
0.36V MAX
4.3V
0.23V
5.45V
5.45V5.11V
1.5-5.5V
INST LINE VOLTAGE
(329V)
5006
5007
2105 470p 3105
6R8
5103
2107 1n
5106
2120 220p
3134 470K
PFC
2113 100uF
1222-1 1222-4
FROM AC SW BOARD
GND_HA
GND_B
STARTUP VOLTAGE FOR FULL POWER SECTION
GND_B
GND_B
GND_B
GND_B
GND_B
GND_C
GND_B GND_B
GND_B
GND_B
PFCOUT
CL 96532100_087.eps
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18 4. Power supply MG5.1E
4.2 Full power factor correction circuit
Personal notes
An explanation of the full Power Factor Correction circuit is now
given. (Figure 4-6) The Power Factor Correction circuit is a
fixed-frequency Pulse-Width modulated boost regulator power
supply. Operating frequency is approximately 60 kilohertz. Due
to the low power consumption of the set during the standby
mode, the Power Factor Correction circuit is turned Off. The
operating voltage, PFC, on Pin 19 of 7102 is turned Off. When
the set is turned On, the operating voltage is switched to Pin 19
of 7102. Once the circuit is in operation, a 5.11 volt internal
reference voltage on Pin 11 is applied to Pin 6 of the IC. Output
of the bridge rectifier is fed to the IC on Pins 4 and 7. Feedback
from the output circuit is fed to Pin 14 where it is multiplied with
the Bridge output. Inputs to the Gilberts Multiplier produce an
error signal that is fed to the current amplifier. The Gilberts
Multiplier multiplies the bridge output voltage with the output
voltage on D438. The 5.11 volt reference is used to provide a
clamping reference for the other inputs. Input current is
sampled by resistors 3130, 3131, 3132, and 3133. This sample
is added to the error signal from the Multiplier going into Pin 8.
The error signal is amplified and then compared to the oscillator
ramp to determine the reset point for the latch. When the
oscillator goes low, the latch is set making output "Q" High. With
the other inputs to the AND gate High, Pin 20 then goes High,
turning 7104 On. By comparing the input and output voltage,
the On time of 7104 is increased when the AC voltage is at its
low point to maintain the 350 volt DC output. When the AC input
voltage is at its peak, 7104 is On for a shorter period.
The IPK circuit connected to Pin 2 is an overcurrent protection
circuit which resets the latch if there is excessive current
through the return resistors. This will reduce the On time of
7104. In a like manner, the OVP, Over Voltage Protection,
circuit will reset the latch removing drive to Pin 20 is the output
voltage exceeds 392 volts.
To check the operation of this circuit when the set is operating
correctly, check the PFCOUT voltage. This voltage should be
approximately 350 volts. If the output voltage is approximately
329 volts, this circuit is not working. Check the operating
voltage on Pin 19 of 7102. Then check the output drive on Pin
20 and at the gate of 7104. There are three grounds on the Hot
side of the supply. Ground HA is connected directly to the
bridge 6000. Ground "B" is the ground for the Power Factor
Correction circuit. If the current sensing resistors 3130 through
3133 should open, this would remove the ground for all the
switching supplies and make the set inoperative. Ground "C" is
the ground for the switching supplies. When ground "B" passes
through the choke 5106, it becomes ground "C".
Startup up voltage for the Full Power supply is taken from the
neutral side of the AC mains.

MG5.1E 4. Power supply 19
4.3 F ull power suppl y
Figure 4-7
UNDER VOLTAGE LOCKOUT 9.4/14.5
REFERENCE SECTION OSCILLATOR STANDBY
OVERVOLTAGE
17V
DEMAG
- +
-
+
FB
FLIP FLOP
S R
Q
SOFT START
A
B
C
18V VCC
VCC
VCC
1V
8
1
16 15 11 10 912
2
3
4 7
13
5
14
7302
2303 100uF
3319 15K
2.5V
3317 15K
2311 1N
2307
2308
3306 10R
3310 330R
3305 10K
6302 6303
3308 0R1
3313 10K 2443
1uF 2442
1N
3461 27K
3446 10
7301
10
11
2346 100N
3447 2.7K
SYNC
3309 0R47
6 8
FROM STBY
2302
6301
3300 22K
STARTUP
1305
ON_OFF
3344 10K
2349
3343 10K
7309
3304 1K
3303 100K
7300
6313
+5VSTBY
+5VSTBY
3316 1K
3315 15K
7303
6
VCC
GND_C
GND_C
GND_C
GND_C GND_C GND_C
GND_C
GND_C
GND_C
5302
3307 33R
6304
3318 150K
VCC
4
PFOUT
6315 3345
470R
3346 470R
2350 470P
6305
2312 470P
5304
2313 470uF
5305
2314 22uF
3330 22K 3331
22K +33V
+130V
5306 6306
2315 470p 63075308 2319 470p
2321 1000uF
14 15 16 17 18 19 12 20 21 22
5307
2316 1000u 2317
1000u 2318
100n
2321 1000u 2322
100n
6309 5313 1302
4A
2330 470u 2331
100n
5314
2332 100n
-15V
-35V +35V
2319 470p
6308 2323 470p
5310 1301
4A
2324 2m2
2325 100n 5312
2327 470u 2326
100n
+15V
5312
3329 330R 2328 1u
3328 100R
3326 4K7
3327 100R 3325
10K +130V
1 24
5
7303
2333 2334 3324
150K
3323 2K7
3322 470R
130V ADJ
3321 8K2
3320 8K2
CL 96532100_088.eps
011299
GND-C

20 4. Power supply MG5.1E
4.3 Full power supply
Personal notes
When the set is turned On, the Main Switch Mode power supply
is turned On. (Figure 4-7) This supply produces the +130 volt,
+33 volt, +35 volt, -35 volt, -15 volt, and +15 volt supplies.
When the On/Off line goes Low, transistor 7309 is turned Off,
turning transistor 7300 On. This switches relay 1305 On.
Startup voltage from the neutral side of the AC mains will
charge capacitor 2303 to 14.5 volts which will overcome the
undervoltage lockout of IC 7302. After the Soft Start capacitor
2443 charges, the oscillator inside the IC will turn On. Each
cycle of the oscillator will set the flip-flop which will cause Pin 3
to go High. This will turn the FET switch 7301 On. Voltage is
applied to the Drain of 7301 through Pins 4 and 8 of 5300 from
the Power Factor Correction circuit. Current through sensing
resistors 3308 and 3309 will develop a voltage which is applied
to comparator "B" connected to Pin 7. When the voltage on Pin
7 reaches the reference voltage on the inverting input, the Flip-
Flop will be reset. The voltage on the inverting side of
comparator "B" is limited to 1 volt. Therefore, the ramp voltage
on Pin 7 will not exceed 1 volt. The circuit will continue to
operate until the charge on capacitor 2303 falls below 9.4 volts
shutting the IC Off. Each time 7301 is turned On, energy is
stored in transformer 5300. Voltage from the Hot secondary on
Pin 10 is rectified by 6301. When the output of this circuit has
sufficient energy to maintain 2303 above 9.4 volts, the IC then
operates in steady state.
When IC 7302 develops a normal steady state operation, the
130 volt supply is sampled by resistors 3324, 3323, and 3322.
This sample voltage is then sent to Shunt regulator 7303 which
drives the feedback optoisolator 7303. The feedback voltage on
Pin 14 is then compared with an internal 2.5 volt reference by
comparator "C". Comparator "C" then sets the reference
voltage on the inverting side of comparator "B" to control the On
time of the drive at Pin 3. If the voltage on Pin 14 increases due
to the 130 volt supply increasing, the On time of the pulse on
Pin 3 will be reduced. If the 130 volt supply decreases, the
voltage on Pln 14 would decrease, causing the On time of the
pulse on Pin 3 to increase. This is used to keep the 130 volt
supply at the correct voltage. Variable resistor 3322 is used to
adjust the 130 volt supply to the correct level.
The overvoltage protection circuit of the IC will shut the IC down
if the VCC level on Pin 1 exceeds 17 volts.
To troubleshoot this circuit, first check the On/Off line from the
Small Signal Panel to ensure that it is going Low. Then check
for the presence of startup voltage on Pin 1 of the regulator IC
7302. If the IC is working correctly, this voltage will be changing
from 9.4 to 14.5 volts. If the startup voltage is not present, check
the startup resistor 3300 and the bridge rectifier. If the voltage
on Pin 1 is changing, check the drive signal on Pin3. Then
check for signal on the gate and drain of 7301. An excessive
load on the secondary, a short on the 130 volt line for example,
would cause the supply to pulse with little or no voltage on the
secondary.