Philips EM7U LCOS User manual

PHILIPS SERVICE AND QUALITY/TRAINING
ONE PHILIPS DRIVE
PO BOX 14810
KNOXVILLE, TN 37914-1810
PHONE: [phone]
FAX: [phone]
EMAIL: [email protected]
PHILIPS
TECH
VIDEOTAPE S
MANUALS
TRAINING
PHILIPS SERVICE AND QUALITY/TRAINING
LCOS
LIQUID CRYSTAL ON SILICON
EM7U LCOS REAR PROJECTION TV

Table of Contents
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
Set Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2
Remote Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
Picture Formats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4
Reflective CD Projection System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
Power Supply Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
AC Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8
Standby Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Main Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
3.3 Volt Regulator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Audio Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
amp Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Video Signal Flow Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Overall Block 1FH Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Side Jack Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
AV1 Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
1H Component Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
1FH Jack Panel Switching . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Main Tuner . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
HIP (High-end Input Processor) Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .30
NTSC Comb Filter Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .32
PIP/Double Window Input . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Double Window PIP Output . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Double Window Control and Power Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Feature Box . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Eagle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
VDS Transmitter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
2H Section Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
AV3 and AV4 Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
Analog Input A/D Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
Reference Voltage and A/D Converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
Input atch and P D Sync . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
ADC Clock Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
ight Engine Block . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
Audio Signal Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
Audio Power Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74
Audio Protection Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
Center Channel Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
Headphone Switch and Amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78
OTC Communication . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
ight Sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Keyboard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
I2C Interconnect - Part One . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
ED Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
I2C Interconnect - Part Two . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
I2C Interconnect - Part Three . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Fan Drive Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87
Wiring Interconnect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91
Disassembly . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94

INTRODUCTION
The EM7U chassis is designated for release in the 2003 model year This is a rear projector
based on LCOS (Liquid Crystal on Silicon) technology LCOS is a reflective LCD technology
The light source is an ARC projection lamp that is replaceable by the customer This projec-
tor is lighter and more compact that comparable size projection sets using tubes They will
be available in 44 and 55 inch screen sizes All of the screen sizes will have a 16x9 aspect
ratio The following table shows the dimensions and weights
Screen size Height Width Depth Weight
44 inch 31 7" 46 7" 14 6" 68 8 lbs
55 inch 38 7" 57" 17 7" 83 9lbs
The EM7U will come in the Epic and Matchline formats The Matchline version will have
Pixel Plus for the 1H inputs The EM7U is a High Definition Ready set with a screen resolu-
tion of 1280x720 It does not have a ATSC Tuner built in A Set Top box will be required for
viewing ATSC signals
44 INCH LCOS PROJECTOR
Page 1
INPUTS
2 1FH INPUTS
1 COMPONENT
3 SVHS
3 COMPOSITE
4 2FH INPUTS
2 COMPONENT
1 RGB
1 DVI

SET OPERATION
The set has three 1H or NTSC only inputs. They are AV1 and AV2 located on the rear ack
Panel. The third input is the Side ack panel. AV3 and AV4 can be either 1H NTSC, 480P,
or 1080I signals. These signals must be in the Y Pb Pr format. AV5 is a DB15 RBG input.
AV6 is a DVI 1080I input connector. The RF input on the Rear ack panel is for NTSC only.
The MON OUT is a monitor output for whichever 1H Tuner, AV1, AV2, or Side ack panel
signal has been selected.
REAR ACK PANEL
The indicator LEDs and the Remote Control
Receiver are located on the front of the set. When
the set is turned On, the Amber LED will turn On.
After the Lamp in the set has switched On, the
Green LED will turn On.
The Control Panel is located at the top of the set.
The Power On button is lighted with a blue LED
whenever power is applied to the set.
Page 2

Remote Control Figure 1
When the set is turned On via the Keyboard or Remote Control, the set will take
approximately 3 seconds to display a picture. By using the Select button, the
Remote can be used to control other devices. A list of setup codes for other
devices is located in the customer's operator’s manual. The customer can select
the Menu button on the Remote to make additional selections and adjustments as
desired. Use the cursor right and cursor down buttons on the Remote to select the
desired topic.
When Picture is selected, use the cursor down
button to select the desired subtopic. For example, press the
cursor down button to select Contrast then use the cursor left
and cursor right buttons to change the values. Additional dots
on the lower part of the line indicate that additional selections
are present. Continue to press the cursor down button to make
these selections.
When Picture is selected, use the
cursor down button to select the
desired subtopic. (Figure 2) For example, press the cursor
down button to select Contrast then use the cursor left and cur-
sor right buttons to change the values. Additional dots on the
lower part of the line indicate that additional selections are pre-
sent. Continue to press the cursor down button to make these
selections.
Under Color Temperature, there are
three selections: Normal, Warm,
and Cool. (Figure 3) With the Normal selection, the picture dis-
plays a normal Gray Scale. If the customer desires a reddish tint
to the picture, Warm is selected. Cool shifts the picture's gray
scale in the direction of Blue.
With sets with Pixel Plus, the C
customer can select between
Progressive Scan and Pixel Plus.
(Figure 4) Pixel Plus provides additional picture enhancement.
FIGURE 1 - MAIN MENU
FIGURE 2 - PICTURE
SELECTION
FIGURE 3 - COLOR
TEMPERATURE
FIGURE 4 - PIXEL
PLUS SELECTION
Pictures with Pixel Plus Off (left) and On (right).
Page 3

Picture Formats
There are seven different Picture Formats: Super Zoom,
Panoramic, 4:3, Movie Expand 14:9, Movie expand 1 :9, 1 :9
Subtitle, or Wide screen, which can be selected by the cus-
tomer. (Figure 5) When portions of the picture are deleted, the
cursor buttons on the Remote can shift the picture to select the
area to be deleted.
Super Zoom enlarges the picture vertically
without distortion. (Figure ) Some of the top and bottom portions of
the picture will be deleted.
The Panoramic format evenly stretches the
edges while keeping the center of the picture
linear to display a 4:3 picture on a 1 :9 screen. (Figure 7)
The 4x3 Format displays a 4:3 picture without
change. Black or gray bars will show at the left
and right sides. (Figure 8) There is no loss of picture on the top and
bottom.
Movie Expand 14:9 displays the picture in a
14:9 aspect ratio. Some of the top and bottom
portions of the picture will be deleted. Black or gray bars will show at
the left and right sides. (Figure 9) This would be used by the viewer if
the original material was in the 14x9 letterbox format.
Movie Expand 1 :9 format stretches the picture
horizontally and vertically to fill the 1 :9 screen. Some of the top and
bottom portions of the picture will be deleted. (Figure 10) This Format
would be used by the viewer if the original material was in the 1 x9
letterbox format.
The 1 :9 Subtitle format zooms the picture for a
full view of subtitles or other information dis-
played at the bottom of the screen. (Figure 11) The top portion of the
picture will be deleted in this mode. This Format digitally stretches the
picture vertically, then shifts it up.
The Wide Screen format evenly stretches the width of a 4:3 picture to
fill the screen. (Figure 12) The viewer would use this Format if the
original material was in a 1 x9 compressed Format.
FIGURE 5 - PICTURE
FORMATS
FIGURE - SUPER
ZOOM
FIGURE 7 -
PANORAMIC MODE
FIGURE 8 - 4x3
MODE
FIGURE 9 - 14x9
EXPAND FORMAT
FIGURE 10 - 1 x9
EXPAND FORMAT
FIGURE 11 - 1 x9
SUBTITLE FORMAT
FIGURE 12 - WIDE
SCREEN FORMAT
Page 4

Under the Channels title, is the channel guide lock selection.
(Figure 13) The customer can lock out selected channels or
channels that are transmitting a selected rating code. These
channels can only be view when the code selected by the cus
tomer is entered. If the customer forgets the code, a code of
0711 entered twice can be used to unlock the set.
A dust filter
is located
under the
Power Cord
to prevent dust buildup in the set. (Figure
14) This is an item that can be replaced
by the customer. Under certain
conditions, if this filter becomes dirty, the
set could overheat and shut down.
The projection lamp is replaceable by the customer.
(Figure 15) A door near the Power Cord allows
access to the Lamp. When this door is open, an
interlock switch will prevent the set from being
turned On. When the back cover is removed, the
switched is in the closed position allowing the set to
be serviced.
A timer in the set will
inform the customer
when the Lamp should
be changed. Under
the Settings/General
title, the Bulb Replaced
selection will reset the
timer when the OK but
ton on the Remote is
pressed. (Figure 16)
The Timer is set for 6000 hours.
When the set is turned On, it takes approximately 30 seconds before the lamp will turn On.
There is an approximate 30 second shutdown time before the set turns Off and can be turned
On again.
FIGURE 13 CHANNEL
LOCKING
FIGURE 14 DUST FILTER REMOVAL
FIGURE 15 PROJECTION
LAMP REPLACEMENT
FIGURE 16 LAMP
TIMER RESET
Page 5
REPLACEMENT PROJECTION LAMP

REFLECTIVE LCD PROJECTION SYSTEM
The LCOS (Liquid Crystal o Silico ) uses a reflective LCD
system. A si gle reflective LCD pa el with multiple LCD
cells is used. Si ce a si gle pa el is used, it is ecessary
to sca the pa el with the primary colors to obtai a color
picture. A LCD is a light valve which allows more or less
light through it, depe di g o the applied voltage. See
Figure 17.
The LCD used i most projectors a d direct view LCD TVs
uses a tra smissive type of LCD. (Figure 18) Light is pro-
jected to pass through the LCD pa el. O e of the disad-
va tages of this type of system is that the electro ics to
co trol the LCD cells limit the surface area i which light
ca pass. This limits the resolutio of the picture a d
bright ess.
The Reflective type of LCD, like the o e used i the LCOS, has
the electro ics be eath the LCD cells, allowi g greater resolutio .
(Figure 19) The LCD cells are tur ed O , switchi g the i dividual
cells. Be eath each cell is a reflective surface. The amou t of
light reflected from each cell depe ds o the applied voltage.
Si ce the LCD may be illumi ated by all three primary colors at
o e time, several cells are addressed at o ce.
The Reflective LCD used i the LCOS projector uses a 1280x1024
device with 20 micro pixels. Si ce the aspect ratio of the TV is
16x9, the actual area used is 1280x720. (Figure 20)
Regardless of the format of the i put, the LCD displays the picture
i a 1280x720 format.
FIGURE 17 - LCD CELL
FIGURE 18 -
TRANSMISSIVE LCD
FIGURE 19 - REFLECTIVE LCD
FIGURE 20 - LCD SURFACE AREA
Page 6

The Philips LCOS projector uses a single LCD device. To obtain a color picture, the LCD is
scanned with strips of Red, reen, and Blue light. The strips of color are developed by split-
ting the light from the Lamp and directing it to three color filters which produce Red, reen,
and Blue light. The output from the filters is directed to three rotating Prisms to produce the
color strips and direct it to the correct part of the LCD. Data is directed to the LCD in such a
way that the correct data for color illuminating that portion of the LCD will be displayed. The
LCD is being scanned a rate of 180 Hz. The phase of each prism is offset by 30 degrees to
provide color separation. The reflected light from the LCD is fed to a projection lens, the mir-
ror, and finally the screen.
Page 7
LAMP
DRIVER
LAMP
LI HT SENSOR
SCANNIN PRISM
LIQUID
CRYSTAL
DISPLAY
PROJECTION LENS
LI HT EN INE WITHOUT LAMP AND PC BOARD
LI HT EN INE LI HT PATH
PRISM

POWER SUPPLY BLOCK (Figure 21)
The Bridge Rectifiers, O /Off Relay, Audio Power supply, a d Lamp supply are located o the
Power I put board. The Sta dby a d Mai supplies are located o the Mai Power board.
AC is applied to the Power I put Board via co ector 1212. This voltage is rectified to pro-
duce the RAWDC-STBY a d is fed to the Mai Power Board. This feeds the Sta dby Supply
that produces a +5V2 supply. This supply feeds the Power Relay o the Power I put board
a d the SSB to power the Microprocessor.
The AC i put voltage is also fed to a Switch co trolled by the Microprocessor o the SSB via
the System Board. Whe the set is tur ed O , the Sta dby li e goes Low, switchi g the
Relay O . This is fed to a rectifier that supplies RAW_DC to the Audio Supply a d Lamp
Supply located o the Power I put Board. The rectifier is co ected as a voltage doubler. It
also supplies RAW_DC to the Mai Supply located o the Mai Power Board. The Audio
Supply provides a positive a d egative voltage to the Audio Amplifier Board. The Lamp
Supply is a Boost regulator that supplies 330 volts to the Lamp Driver board.
The Mai Supply produces a +36, a +12, a +22 a d a +9 volt supply. The +9 volt supply is
also fed to a 3.3 volt regulator.
AC INPUT (Figure 22)
AC power is co ected to the Power I put board via co ector 1212. Fuse 1211 provides
protectio agai st overcurre t. Spark gaps 1214 a d 1216 provide protectio agai st exces-
sive voltage spikes o the AC li e. Resistors 3207, 3210, 3213, a d 3215 limit the curre t
whe power is first applied to the set. Bridge 6202 rectifies the AC voltage to produce the
RAWDC_STBY for the Sta dby regulator.
Bridge 6201 provides power for the Lamp Supply a d the Mai Power supply. Whe the set
is tur ed O , Relay 1210 switches O to provide power to 6201. Bridge 6201, Capacitors
2202 a d 2209 co stitute a voltage doubler circuit. Whe the set is tur ed O , the Sta dby
li e goes Low. Tra sistor 7212 tur s O tur i g tra sistor 7211 O , switchi g the Relay 7210
O . The grou d side of the Relay is co ected to the Lamp Door I terlock switch a d the
Thermal switch which is located o the Lamp Housi g. If the Projectio Lamp Door is ope
or the Lamp Housi g has overheated, the set ca ot be tur ed O .
Page 8

POWER INPUT BOARD
MAIN POWER BOARD
POWER BOARD SERVICE
POSITION
Page 9

Page 10
FIGURE 21 - POWER SUPPLY BLOCK

Page 11 FIGURE 22 - AC INPUT CIRCUIT

STANDBY SUPPLY (Figure 23)
The Standby supply is l cated n the Main P wer b ard. It pr vides the +5VSTBY supply t
the set whenever p wer is applied.
When p wer is first applied, the RAWDC_STBY is applied t the primary winding f 5210 and
t Pin 7 f 7202. Current thr ugh resist r Rs charges Capacit r 2244 c nnected t Pin 1 f
7202. When the charge n 2244 reaches 5.8 v lts, the Internal Supply switch is switched t
internal. The Oscillat r and PWM turn On t drive the internal FET. The PWM will c ntinue
t drive the FET until the charge n Capacit r 2244 dr ps bel w 4.8 v lts. Capacit r 2244
will again charge and the pr cess will repeat. With each startup cycle, energy is transferred
t the sec ndary windings f 5210. When the +5VSTBY supply reaches 5 v lts, the input f
7206 will g t 2.5 v lts. This will turn Shunt Regulat r 7206 On, causing current t fl w
thr ugh pt is lat r 6207. V ltage fr m Pins 1 and 2 f 5210 is rectified by 6205 t pr duce
the perating v ltage f r 7202. When Opt is lat r 6207 turns On, the perating v ltage is
applied t Pin 1 f 7202. The supply is in a n rmal perating m de.
Regulati n f the sec ndary is acc mplished by m nit ring the reference v ltage via Shunt
Regulat r 7206 and pt is lat r 6207. The +5VSTBY is the reference v ltage f r the
Standby supply. If the 5-v lt standby supply sh uld increase, Shunt Regulat r 7206 will c n-
duct harder, causing the LED in Opt is lat r 6207 t get brighter. The internal resistance f
the transist r inside 6207 will be reduced. The internal regulat r inside 7202 c nnected t
Pin 1 w rks t keep Pin 1 at 5.8 v lts. If the current thr ugh 6207 increases, the current fl w
thr ugh the 5.8-v lt regulat r will increase. This increase in current will cause the v ltage
acr ss the sensing resist r Re t increase. The PWM will then reduce the On time f the
internal FET, reducing the sec ndary v ltage. If the 5-v lt standby v ltage sh uld decrease,
the current thr ugh the sensing resist r Re will decrease, reducing the v ltage acr ss the
resist r. This will cause the PWM t turn the internal FET On f r a l nger peri d f time,
increasing the sec ndary v ltage.
The +5.2 v lt supply is switched by FET 7203 when the +12 v lt supply fr m the Main P wer
supply is switched On. If the Standby Supply sh uld fail r P wer is rem ved fr m the set,
the Standby P wer Fail circuit will signal the Micr pr cess r in time t all w it t shut d wn.
V ltage fr m Pin 8 f 5210 is rectified by 6209 t pr duce a negative v ltage. This v ltage
and the +5 v lt standby v ltage is applied t the input f Shut Regulat r 7209. The c mbined
v ltage keeps the input t 7209 bel w the turn On v ltage f 2.5 v lts. A small Capacit r,
2265, filters the negative v ltage that is rectified by 6209. If p wer is rem ved fr m the set,
2265 will discharge quickly because f its small value. The input t 7209 will then g ab ve
2.5 v lts, turning it On. This will turn transist r 7210 On, switching the Standby P wer Fail
line High. Transist r 7210 will als turn On, turning the +5.2 v lt supply Off.
Page 12

Page 13 FIGURE 23 - STANDBY SUPPLY

MAIN POWER SUPPLY (Figure 24)
Power is applied o he Main Power supply when he se is urned On. The RAW-DC is
swi ched o he Main Power supply loca ed on he Main Power supply board. Vol age is
applied o he Primary winding of 5310 via Pins 5 and 3. Vol age is hen applied o Pin 7 of
7302. In he S ar up mode, vol age from he in ernal curren limi ing resis or Rs is rou ed o
Pin 1 where i charges Capaci or 2344. When he charge on Capaci or 2344 reaches 5.8
vol s, Pin 1 is swi ched o he In ernal Supply connec ion. The Oscilla or and PWM drive are
swi ched On o drive 5310. IC 7302 will con inue o drive he Transformer, 5310, un il he
charge on 2344 drops below 4.8 vol s. The S ar up cycles will con inue un il he secondary
reference vol age, he 9 vol s supply, reaches he correc level. When he 9-vol supply
reaches he correc level, 2.5 vol s will be applied o he inpu of Shun Regula or 7306.
Shun Regula or 7306 will hen urn On causing curren o flow hrough he LED in
Op oisola or 6307. This will urn he ransis or inside 6307 o urn On. Vol age from Pins 1
and 2 of he Ho secondary is rec ified by 6305 and fil ered by 2341. Op oisola or 6307
swi ches his vol age o Pin 1 of 7302 o provide he opera ing vol age for he IC.
The secondary produces +36, +12, +9, and +22 vol supplies. Shun Regula or 7304 and
FET 7303 regula e he +12 vol supply.
The PWR_FAIL Main Power Fail de ec ion circui signals he Microprocessor when power is
abou o be los o he se while i is On. Vol age from Pin 9 of 5310 is rec ified by 6309 o
produce a nega ive vol age, which is fil ered by Capaci or 2365. This vol age along wi h he
+9 vol supply is applied o he inpu of Shun regula or 7309 via resis or ne work of 3354,
3355, and 3353. As long as he nega ive vol age is presen on 2365, he vol age on he inpu
of 7309 will be less han he 2.5 vol s necessary o urn i On. Transis or 7310 will be urned
Off, keeping he PWR_FAIL line Low. When he swi ched mode supply ceases opera ion,
Capaci or 2365 will discharge quickly, due o i s low value, allowing he vol age on he inpu of
7309 o increase o 2.5 vol s. Shun Regula or 7309 will urn On, urning ransis or 7310 On,
causing he PWR_FAIL line o go High. This will signal he Microprocessor o shu every hing
down before he main supply vol age drops.
Regula ion of he secondary is accomplished by moni oring he reference vol age, he +9 vol
supply, o con rol he On ime of he in ernal FET of 7302. If he +9 vol supply increases,
Shun Regula or 7306 will conduc harder increasing he amoun of curren hrough 6307.
This will cause he LED o increase in brigh ness, reducing he in ernal resis ance of he ran-
sis or inside he IC. The increase in curren will cause he vol age across he in ernal sensing
resis or Re inside 7302 o increase. The PWM will hen reduce he On ime of he in ernal
FET, decreasing he secondary vol age. If he +9 vol supply should decrease, 7306 will con-
duc less, he ransis or inside 6307 will conduc less, causing less curren o flow hrough he
sensing resis or Re. The PWM will sense he lower vol age across Re, increasing he On
ime of he in ernal FET o increase he secondary vol age.
Page 14

Page 15 FIGURE 24 - MAIN POWER SUPPLY

3.3 VOLT REGULATOR (Figure 25)
IC 7307 and transist r 7308 make up the 3.3-v lt regulat r l cated n the Main P wer Supply
b ard. When the Oscillat r in 7307 g es L w, the flip-fl p is reset causing Q t g L w and
the utput t g High. When the Feedback v ltage n Pin 5 is bel w 1.25 v lts, the
c mparat r utputs a High. When the Oscillat r g es High, the flip-fl p is Set, causing Q t
g High. This causes Pin 1 t g L w, turning Transist r 7308 On. 7308 will stay n until the
Oscillat r g es L w, resetting the flip-fl p. If the utput v ltage m nit red n Pin 5 g es
bel w 3.3 v lts, the v ltage n Pin 5 will dr p bel w the 1.25 v lt reference. The flip-fl p will
then Set when the Oscillat r g es High. If the utput v ltage g es ab ve 3.3 v lts, the
reference v ltage n Pin 5 will be ab ve the 1.25 v lt internal reference. The flip-fl p will n t
Set when the Oscillat r g es High until the feedback reference v ltage n Pin 5 dr ps bel w
the 1.25 v lt internal reference. This meth d c ntr ls the On time f 7308 t regulate the
3.3-v lt supply. Pin 7 m nit rs the current by reading the v ltage dr p acr ss resist rs 3349
and 3351. If the utput current is excessive, the Oscillat r will g L w t sh rten the On time
f 7308.
Page 16
POWER INPUT BOARD IN SERVICE POSITION MAIN POWER BOARD

Page 17 FIGURE 25 - 3.3-VOLT REGULATOR