Grundig GT 2105 User manual

Service
Manual
Sach-Nr./Part No.
72010-019.10
Service
Manual
Sicherheit
Safety
Sach-Nr./Part No.
72010-800.00
Additionally
required Service
Manuals for the
Complete Service:
Änderungen vorbehalten Printed in Germany Service Manual Sach-Nr.
Subject to alteration VK 221 0596 Service Manual Part No. 72010-019.10
SERVICE MANUAL
D
Btx *32700 #
GT 2005 (77250-056.61/GCC 1261GB)
GT 2105 (77250-055.61/GCC 1361GB)
TRC 1 (75990-200.14)
TRC 2 (75990-300.00)
.
Attention: The picture tube panel must be removed
before disconnecting the yoke plug
Chassis G 1000 Stereo (ST 03)

GRUNDIG Service1 - 2
General Section ST 03
Table of Contents
Page
General Section .....................................1-1... 1-8
Safety Advice ............................................................................... 1-2
Technical Data..............................................................................1-2
Remote Control TRC 1 .................................................................1-3
Remote Control TRC 2 .................................................................1-3
Brief Service Instuctions ...............................................................1-4
Fasttext Operation ........................................................................1-4
Operating Hints.............................................................................1-5
Circuit Descriptions..............................2-1... 2-3
1. Power Supply .........................................................................2-1
2. Tuner and Demodulator Circuits ............................................ 2-1
3. Peritel Output .........................................................................2-1
4. Video Chroma Processing .....................................................2-1
5. Delay Line ..............................................................................2-1
6. Time Base Generator .............................................................2-2
7. RGB Drivers ...........................................................................2-2
8. System Microcontroller (IC500)..............................................2-2
9. Output Power Stages .............................................................2-3
10. Video Output Stages ..............................................................2-3
11. Teletext Options......................................................................2-3
12. Power Supply to MSP 3400/3410 ..........................................2-3
13. Second Peritel and Mute Circuit............................................. 2-3
14. Audio Amplifier........................................................................2-3
Alignment ....................................................... 3-1
Layout of the PCBs
and Circuit Diagrams.........................4-1... 4-22
Chassis Board ..............................................................................4-1
Oscillograms ................................................................................ 4-8
Deflection H+V............................................................................4-10
Power Supply............................................................................. 4-11
Signal Board .............................................................................. 4-13
Y/C Processing ...........................................................................4-15
Audio Board Circuit Diagram ......................................................4-17
Audio Board PCB........................................................................4-19
Text ............................................................................................ 4-21
CRT Panel ................................................................................. 4-21
Spare Parts List ....................................5-1... 5-4
Safety Advice
The X-radiation developing in the sets conforms to the X-radiation
Regulations (January 8, 1987), issued by the Physikalisch-Techni-
sche Bundesanstalt (federal physiotechnical institution).
The high tension for the picture tube and thus the developing X-
radiation depends on the precise adjustment of the +A power
supply.
Aftereveryrepairofthepowersupplyunitorthehorizontaldeflection
stageitisimperativethattheEHTforthepicturetubeischeckedand
re-adjusted if necessary.
To avoid consequential damages to the chassis or the picture tube
the integrated protective circuits are allowed to be put out of
operation only for a short time.
When replacing the picture tube use only the types specified in the
spare parts lists.
Technical Data
TV Receivers .............................................. 20" / 21"
Mains voltage.............................................. 220…240V ~ 50/60Hz
Control range of the power supply ..............190…264V
Screen diagonal.......................................... 51cm / 55cm
Picture diagonal .......................................... 48cm / 52cm
Power consumption .....................................ca. 55W
Power consumption in Standby ...................ca. 8W
Aerial socket ............................................... 75 Ωcoaxial plug
Programmes ............................................... 99 + 2AV
Standard ..................................................... PAL/I
Output power .............................................. 2x5W RMS
Temperature range ......................................0 - 40°C
General Part
Test Equipment / Aids
Variable isolating transformer Test/Sweep Generator
Colour Generator Oscilloscope
DC Voltmeter AF Voltmeter
AF Generator Frequency counter
Please note the Grundig Catalog "Test and Measuring Equipment"
obtainable from:
Grundig electronics GmbH
Würzburger Str. 150
D-90766 Fürth/Bay.
Tel.[phone]
Telefax 0911/703-4479
Theregulationsandsafetyinstructions shall bevalidasprovidedbythe"Safety"ServiceManual,part
number 72010-800.00, as well as the respective national deviations.

GRUNDIG Service 1 - 3
ST 03 General Section
Remote Control TRC 2
123
456
789
0/AV
VOL-
VOL+
P+
P-
MENU
TUNE
TV
STORE
TEXT/MIXHOLD EXP
e
8
6
AUDIO
LANG 1/2 STEREO
INDEX
TRC 2
A
P
O
N
M
L
H
J
G
F
D
C
B
K
E
I
Q
R
S
Operation of the Remote Control Keys
A Directchannelselectionorpagenumberinteletextmode.Switches
the television on from standby.
B Switches set to standby or switches set on from standby
C Increases and decreases the volume
D Displays the selected channel
E Stores channels in tuning mode
F Increases or decreases adjustable settings
G Returns to normal viewing mode
H Mutes sound
I Selects teletext/selects mixed mode (text on picture)
J Changes height of characters in teletext mode
K Fasttext buttons
L Holds a selected page in teletext mode
M Selects index pages in teletext mode
N Selects between stereo, stereo-wide and pseudo-stereo
O Selects language in dual language Nicam transmissions.
Selects mono sounds.
P Accesses menu
Q Accesses audio selections
R Selects tuning mode
S Selects auxiliary input
Remote Control TRC 1
Operation of the Remote Control Keys
8Switches the receiver on and off (Standby)
1-0 Directchannelselectionanddirectentryofadjustable
settings. Turns television on from Standby.
P+ Selects channel above current channel. Increases
adjustable menu settings.
P- Selects channel below current channel. Decreases
adjustable menu settings.
VOL+ Increases Volume
VOL- Decreases Volume
i Displays selected channel number. Accesses hidden
information.
MENU Accesses Menu
STORE Stores channels in tuning mode
TUNE Selects tuning mode
eMutes sound
HOLD Holds a particular page in the Teletext mode
EXP Changes height of characters in the Teletext mode
TEXT/MIX Selects teletext/selects mixed mode (text on picture)
TV Returns to normal viewing mode
0/AV Selects auxiliary mode
123
456
789
0/AV
VOL-
VOL+
P+
P- MENU
TV
TUNE STORE
TEXT/MIX
HOLD EXP
e
8
6
TRC 1

GRUNDIG Service1 - 4
General Section ST 03
Brief Service Instructions
Tuning
Press the "Tune" key on the remote control to bring up the tuning
graphic"S".Pressandholdthe"P+"keyformorethan1secondtostart
the search tuning. When a channel is found the "S" graphic will flash.
Eitherselect"P+"tocontinuetuningor"Store"toretainthechannel.By
pressing the "Store" key the programme number will flash, key in the
programmenumberthatthechannelistobestorein.Toexitthetuning
screen press TV.
Fine Tuning
Pressthe"Tune"buttonandthenthe"HOLD"keybrieflytobringupthe
finetuninggraphic.AnXwillappearafterthechannelnumber.Usethe
"P+" and "P-" keys to fine tune and then "Store".
Scart Menu
Press the "0/AV" button and then the "Tune" key the Scart options
graphic will appear, with VCR, DECoder and AUX. In the VCR mode
only, the line time base time constant is short. In Decoder mode Pin 8
of the Scart is enabled whilst tuning to allow for tuning of decoded
channels.
Fasttext Operation
In addition to the standard Teletext functions, the receiver GT 2105
has Fasttext. This system provides more value from Teletext by
allowing fast access to highlighted pages and by linking many related
pages for easy access.
Thekeyto Fasttext is four colour codedpromptsatthebottom of each
teletext page. These red, green, yellow and blue prompts relate to the
four colour coded buttons on the tv remote control.
Each colour coded prompt acts as a "signpost" through the huge
choice of Teletext pages available, allowing faster and easier access
to highlighted pages.
Use of Fasttext
To select any colour coded page from Teletext press the correspond-
ing coloured button on the TV remote control.
Thenewpageselectedwillappearalmostinstantlyalthoughtherecan
still be a delay for some pages to appear. This is particularly the case
if a rapid succession of coloured Fasttext buttons are pressed.
Asnewpagesareaccessed,at the bottom of the page a new series of
subject related colour coded prompts will appear.
Fasttext Index Function
To return any time to the main index pages it is not necessary to enter
the index page number.
INDEX To return to the main index press the INDEX button once.
INDEX With the main index on screen a further press of the INDEX
buttonwillaccessthemainA-Zindexorothersubsidiaryindex
pages.
Returning to Normal Television Viewing
TV To return to normal television viewing at any time, press the
TV button.

GRUNDIG Service 1 - 5
ST 03 General Section
Operating Hints GT 2005 / 2105
Note: This chapter contains excerpts from the operating instructions. For further particulars please refer to the appropriate user instructions the part number of which is indicated in the relevant spare parts list.
5
'S'
TUNING IN
TUNING
Your TV set can memorise 99 different channels.
During channel tuning any connected satellite receiver
or video recorder should be switched to standby. To
tune in different channels, follow the instructions below.
Step 1
Press TUNE on the remote control.
A tuning bar will appear.
Step 2
Press P+ for approximately one second.
The set will scan up through the available channel
frequencies. A cursor moves slowly up the bar until
a channel is found. The Swill now flash on and off.
If you do not wish to store the channel, press P+
again until a required channel is found.
Step 3
Press STORE to memorise the channel.
The programme setting PO1 will now flash on and off.
Step 4
Decide which channel number you want to allocate
the channel to e.g. BBC1 = 1. Press the appropriate
number e.g. 1.
Step 5
Store the setting by pressing STORE.
The channel is now stored against the chosen channel
number. The tuning bar will still be on screen and the
S will still flash.
Now tune the remaining channels. Repeat steps 2, 3, 4
and 5 until all channels are tuned in.
To exit the tuning screen press TV.6x2
FINE TUNING
After following the TUNING instructions you should
have a clear picture on all channels (subject obviously
to the reception quality of the incoming signal). If any
channels are not to the standard you would expect,
fine tuning may sometimes improve the picture quality.
To fine tune follow the steps below:
Step 1
Select the channel to be tuned. If the tuning bar is no
longer on screen press TUNE. If it is, move onto step 2.
Step 2
Press HOLD very briefly. An Xwill appear besides the
programme number to indicate that fine tuning has
been selected.
Step 3
By briefly pressing P+ or P-, fine tune the picture.
Step 4
When the best possible picture has been achieved,
press STORE twice to memorise the settings.
Step 5
To return to normal television viewing press TV.
Note : the Xsymbol means that the Automatic
Frequency Control (AFC) has been switched off.
Channels stored with the Xdisplayed may drift off
tune and therefore fine tuning should only be used if
absolutely necessary.
TUNING INTO A VIDEO RECORDER,
SATELLITE RECEIVER OR GAMES CONSOLE
If connecting a video recorder, satellite receiver or
games console to the television set via the scart
sockets (see page 3 and 14), press 0/AV on the
remote control. Alternate presses of 0/AV selects
between the AV inputs, AV1 and AV2.
If making the connection via the television sets aerial,
select channel 99 as the dedicated channel by
pressing 9twice.

1 - 6 GRUNDIG Service
General Section ST 03
7
With the video recorder, satellite receiver or games
console on, tune channel 99 to the output following
steps 1-5 in the TUNING IN SECTION on pages
4 to 5.
When using the 0/AV mode the on screen display can
be adjusted to indicate whether a video recorder,
external decoder or auxiliary source (e.g. a games
console or satellite receiver) is connected. Follow the
steps below selecting first either AV1 or AV2 input
as required.
Step 1
Press 0/AV on the remote control.
Step 2
Press TUNE on the remote control. The display will
show 3 options;
(vcr)
DEC (decoder)
AUX (satellite receiver or games console).
Step 3
Further pressing of TUNE allows the desired symbol
TUNE to be highlighted in yellow. When the required
symbol is highlighted the setting will automatically store
after five seconds.
STANDBY AND CHANNEL
CONFIRMATION
STANDBY MODE
When the television is in standby it can be switched on
by pressing either P+ or P- or by pressing the channel
number required, e.g. 1for BBC 1. Alternatively press
STANDBY.
CONFIRMATION OF CHANNEL SELECTED
Whenever a new channel is selected the top left hand
corner of the screen will confirm the channel number
selected for approximately 5 seconds.
8
To confirm or check the channel being watched
without changing channel, press i. The channel
number selected will be displayed in the top left hand
corner of the screen for approximately 5 seconds.
Note : Pressing iwill confirm the channel details at the
bottom of the screen.
PICTURE ADJUSTMENT
Your Grundig television set allows control of
brightness, contrast and colour. To make any picture
adjustments follow this procedure :
BRIGHTNESS CONTRAST AND COLOUR
Step 1
Press MENU.
The brightness symbol will be displayed with a cursor
which indicates the current brightness setting.
Step 2
With the cursor on screen adjust the brightness by
using P+ or P-. The cursor moves to indicate the
change. The new setting is automatically stored.
Step 3
To change the other settings, with the brightness
control on screen, press MENU. The brightness symbol
before the cursor will change to the contrast setting.
Step 4
Adjust the contrast by using P+ or P-.
Step 5
With the contrast setting on screen press MENU again.
The contrast symbol before the cursor will change to
the colour setting.
Step 6
Adjust the colour setting to your liking by using
P+ and P-.

GRUNDIG Service 1 - 7
ST 03 General Section
The cursor will move to indicate the change.
To return to normal viewing press TV.
AUDIO ADJUSTMENT
VOLUME CHANGE AND MUTE
To increase the volume press VOL+.
To decrease the volume press VOL-.
To mute the sound, press .
To restore the sound when muted press again.
BASS, TREBLE AND BALANCE ADJUSTMENT
To make the most of high quality NICAM stereo
transmissions you can alter the bass, treble and
balance to your preference. Follow these steps:
Step 1
Press AUDIO until the audio selection screen is
displayed. The bass symbol will be displayed with a
cursor which indicates the current bass level selected.
Step 2
With the cursor on screen adjust the bass level using
P+ or P-. The cursor moves to indicate the change.
Step 3
To change the treble level with the audio selection
screen displayed press AUDIO until the treble
symbol is displayed.
Step 4
With the cursor on screen adjust the treble level
using P+ or P-.
Step 5
To change the balance with the audio selection screen
displayed press AUDIO until the balance symbol
is displayed. 9 10
Step 6
With cursor on screen alter the balance in favour of
the left or right TV speaker with P+ or P-.
Note: If no further buttons are pressed the audio
selection screen will disappear within 5 seconds and
any changes made will be stored.
STEREO WIDE SELECTION
Your Grundig NICAM stereo television allows you to
enhance the stereo effect from stereo transmissions
by selecting Stereo Wide. To select Stereo Wide follow
these steps:
Step 1
Press STEREO. Either (stereo) or
(stereo wide) symbols will appear.
Step 2
Repeated presses of STEREO will alternate between
stereo and stereo wide allowing the selection of
whichever is preferred. Once the required stereo
selection is made the on screen symbol will disappear
after 5 seconds and the selection will be stored.
PSEUDO STEREO SELECTION
If the transmission is not in stereo no symbol will be
displayed. It is possible to give the mono sound a
stereo like sound by following the steps in stereo wide
selection above.
Either (mono) or (pseudo stereo) can be
selected.
MONO SOUND SELECTION
On the edge of a NICAM stereo transmission area the
stereo sound may be intermittent, resulting in poor
sound quality, popping and clicking noises. If this is
the case the programme can be listened to in mono
instead of stereo, by pressing LANG 1/2. The
symbol will indicate that mono sound has been
selected. A second press will restore the stereo
symbol and stereo sound.

1 - 8 GRUNDIG Service
General Section ST 03
ADDITIONAL INFORMATION
CARE OF YOUR SET
Use only a soft cloth to clean your television set
cabinet. Normal window cleaning products can be
used to clean the screen.
Never use strong detergents, abrasive cleaner or
polish to clean either the cabinet or the screen.
SCART USAGE
If only one SCART connector is to be used it is
advisable to use SCART 1. If both are to be used the
following use of Scart connections is likely to be
most suitable:
Products Scart 1 Scart 2
VCR and Satellite Receiver VCR Satellite Receiver
VCR and Games Console Game VCR
VCR and Hi-Fi Hi-Fi VCR
Satellite Receiver and Hi-Fi Hi-Fi Satellite Receiver
11
15
60
MULTI LANGUAGE OPERATION
In the future some television programmes may be
transmitted with a choice of language selections.
Your Grundig television is ready for this development.
If programmes are transmitted in this way, pressing
LANG 1/2 will alternatively select between the dual
language audio soundtracks which will be in mono.
SETTING THE SLEEP TIMER
Should you fall asleep whilst watching television, or
leave the television set on unattended, your Grundig
Television set will automatically switch into standby
10 minutes after the end of transmissions.
You can however, programme the television to switch
into standby between 1 minute and 90 minutes ahead.
This ensures that should you fall asleep before the end
of a programme, the television set will automatically
switch off, instead of remaining on until the end of the
last programme of the day. To activate the sleep timer
follow these steps:
Step 1
Press MENU until the timer off symbol is displayed.
Step 2
Press either P+ or P-. The timer on symbol will be
displayed along with the time in minutes until the
automatic switch off will be activated.
Step 3
Press P+ or P- to set the time in minutes until the
television set will switch off.
Pressing P+ will increase the minutes from 1-90.
Pressing P- will decrease the minutes from 90-1.
When the correct advanced switch off time is selected,
if no further buttons are pressed the set will revert to
normal viewing and automatically switch off after the
pre-determined time. To ensure that the timer will not
activate alter the switch off time to zero. 14

ST 03 Circuit Description
GRUNDIG Service 2 - 1
Circuit Description
1. Power Supply
The power supply is a conventional off line, isolated switch mode
system.AC line voltage isapplied to the circuitviaswitch fuse and the
maininputRFIfilter. The degauss coil supply is takenoffafterthefilter
then the AC is rectified through a bridge circuit comprising D100 to
D103. After filtering by C103 and C104 the DC is now fed to T100
switch mode transformer. TR100 is the switching transistor and it, in
turn, is driven by the UC3844 IC100 which is a PWM (Pulse Width
Modulation) control IC. In the basic chassis, the UC3844 is run as a
fixed frequency PWM controller, the frequency being governed by
R105 and C107.
1.1 HT Adjustment
VR100isusedtosetthe+B,thisvariestheoutputvoltagebycontrolling
the feedback voltage to the IC100. The +B rail is the line measured
when this control is used. This line is set in accordance with the CRT
that is fitted. When this rail is set then any variation in power demand
by the receiver will be reflected in the feedback winding which, in turn,
will appear as an error voltage on IC100-(2). This error voltage will, in
turn,varythePWMoutputtotheswitchingtransistorwhich,inturn,will
maintain the output voltage constant.
1.2 Over Current Protection
The power supply is totally overcurrent protected by sensing the
current through the switching transistor. The combination of R114,
R113, D112, D113, R112 and C113 all act to provide conditioning of
thesensing voltageforthe IC100currentsense input.Ascurrent flows
across TR100 collector-to-emitter junction (source drain for stereo) a
voltageproportionaltothecurrentisproducedacrossR114andR113.
This voltage is fed to Pin 3 current sense pin of IC100. When the
predeterminedthresholdvoltageisreachedbecauseofexcesscurrent
drawn IC100 limits the current to protect the PSU and other circuits.
Aftera periodoftime itwilltrytorestart,ifthe faulthasnotclearedthen
itwillshutdownagain.D112andD113aretheretopreventthevoltage
developed rising to an unacceptable level on the sense pin of the IC.
R112 and C113 provide a degree of filtering of the sense waveform.
T100 also provides the isolation from the AC line to the chassis of the
TV.Allsecondary supplies are isolated so that themain -and external
connections are at ground potential, therefore, safe to the user.
Warning! The heat sink on TR100 is live.
1.3 Supply Regulation
The5V supply for someof the main ICsofthe system is supplied from
the secondary winding of T100, the 9V output is fed into a fixed 5V
voltageregulator.The33Vtunertuningvoltsisderivedfromthe+Bline
using a band gap close tolerance shunt regulator D120.
R115 and C114 are isolation components linking the non-isolated to
the isolated side of the chassis for RFI and electrostatic purposes.
2. Tuner and Demodulator Circuits
The tuner TUN600 can be one of two models depending on what
transmissionsystemisbeingviewed.FortheU.K.usingPALSystem I
thetunerisaSalcomp1590R.ForallotherEuropeanPALandSECAM
systems the tuner is a Salcomp 1490R. Both tuners are pin for pin
compatible, the only difference is that the 1590R is UHF only and the
1490R is a multi band tuner. Both tuners are voltage synthesis types
and tuning voltage is controlled by the system microcontroller IC500.
AGC control of the tuner is determined by the demodulator IC400.
2.1 SAW Filter Options
TheIFoutput of both types oftunerisabalancedoutputand isfedinto
a number of balanced input saws - SAW450, SAW600 and SAW601.
As to which or how many saws are fitted is determined by the options
fittedand the system tobe received.In the stereo chassisSAW 600 is
fitted.
However,thiscanbeadifferenttypeofSAWdependingonthesystem
being received. A system table is presented on the circuit diagram
giving the specific type of SAW to be fitted in the 601 position for each
system.
2.1.1 SECAM L/L (option)
If the chassis is fitted with SECAM L/L the addition of SAW450 is
required for the sound.
2.1.2 Stereo SAW
ShouldthefullstereooptionberequiredthenSAW601isreplacedwith
SAW600 and SAW450 stays as it is if SECAM L/L is also required.
2.2 Vision IF Demodulator
TakingthebasiccasetheoutputsfromwhicheverSAW600or60isfed
to the IF input of the demodulator IC400-(19), -(20) which is an
STV8224. Under most applications there is only one adjustable
component in this circuit and that is L401 tank coil. However, when
SECAM L/L option is required an additional trim capacitor is required
alongwith R416, C412,D532,R417andR425.Theincoming signal is
demodulatedintheSTV8224.Thedemodulatedvideoandintercarrier
sound are then fed out on pin 3 STV8224. The combined signals are
fed into the filter circuits for separation of sound and video. The
separationisachievedbytheuseofceramicfilters.CF400andCF401
are the filters that perform this task.
2.3 Dual System Sound Options
It will be noted that there are two ceramic filters, CF400 and CF401.
Bothsetsarerequiredifdual system operation isrequired.Details are
to be found in the system table on the diagram for each option.
The separated signals are then fed back into the IC400 where the
sound is demodulated and the audio processed. The video and audio
are then routed by the internal switching of IC400. The routing is
controlled by the microcontroller. The external video and audio from
the Peri connector are also fed into this IC.
2.4 Tuner AGC Control
TheSTV8224alsoperformsAGCcontrolforthetuner.Theoperational
threshold for AGC action is controlled by the microcontroller, the
threshold level is set up on IC400-(24).
2.5 SECAM L/L’ Vision IF (option)
In the event of SECAM L/L’ option being required, then additional
IC450 needs to be fitted as does SAW450. This is in order to
demodulate the AM sound of SECAM L/L system. Audio switching is
then re-routed between IC450 and IC400, this is all done under the
system microcontroller software in IC500.
The switching network comprising TR450, TR451, TR452, D450 and
D451isforthepurposeofswitchingtheSAWtransducerwithvariation
in band switching. Because the sound and vision carriers are trans-
posed between Band 1 and Bands III, IV and V, then the balanced IF
output has to be switched to the right transducer on SAW450. The
switchingisagaincontrolledbythesystemmicrocontrollerIC500.The
transducer that is not being used is short circuited by its respective
diode.
3. Peritel Output
ThevideoouttothePericonnectoristakenoffbeforethefilteredsignal
is fed back into IC400. It is then fed to a buffer circuit TR700 and then
to pin 19 of the Peri connector.
4. Video Chroma Processing
IC800isthevideoandchromaprocessingcircuit.Allcontrolsaretotally
under software control. Customer controls can be adjusted from the
frontpanel.Therastercorrectioncontrolsareonlyaccessibleinfactory
set-up and troubleshooting mode set by the system microcontroller.
The customer controls are accessed in this mode, or by the conven-
tional remote control.
The composite video is fed into IC800-(2). Separation of luma and
chroma signals is carried out internally by the sampled data method
usingclocksgeneratedbytheexternalcrystal.This methodisusedfor
all decoding processes in the chip. The sample clock is phase locked
to the subcarrier for correct colour ident.
5. Delay Line
The sample component chroma signals are now fed to a digital,
1 picture line length delay line. The same sample clock is fed to the
delay line IC801 as is fed to the IC800 so that phase relationship is
maintained within the whole system.
5.1 RGB Matrix and Sync Separator
After passing through the delay line it is returned to IC500-(26), -(27)
andthenmixedwiththelumaandfedintothematrixcircuitstoproduce
the RGB output. The luma signal is also fed through a short delay line

Circuit Description ST 03
2 - 2 GRUNDIG Service
whichisintegratedontotheIC800.Thesyncseparationandtimebase
circuits are also integrated on to this chip. Incoming video is stripped
of its line and field sync pulses. The horizontal and vertical syncs are
then derived from the composite sync waveform.
6. Time Base Generator
Thelinesyncisfedtothelinetimebasegeneratorcircuit.Thelinetime
baseis derivedfromthe masterclockoscillator anddividercircuit. The
linepulses fromthedivider arefedintobothPLLcircuitsalong withthe
sync and flyback pulses. These combine together to produce the line
driveforthelineoutputcircuit.TwoPLLtimeconstantsareusedtogive
good lock for both fixed, gen-locked syncs, such as from terrestrial
transmission and from weak or variable sync such as VCR.
All controls for the line time base generator are integrated and are
accessedviatheI2CbusundermicrocontrolfromIC500.Theseareset
up in the factory by a test software.
6.1 Vertical Time Base
The vertical time base is again generated on chip by the use of the
master clock in conjunction with the separated field sync. The divider
circuitcount is controlled by thesyncpulse.The counter produces the
pulsestogeneratethe vertical ramp which is in turn fed toa bufferand
then fed out to the field output circuit.
Inthe event ofnovalidsync being presentthenadirect injection mode
isusedtocontinuethefunctionoftherampgenerator.Thisdirectmode
then enables vertical scan to be maintained in the event of no signal
being present.
7. RGB Drivers
The RGB video signals are fed out on IC800-(17), -(18), -(19). These
signalsarethenbufferedbytheemitterfollowercircuitsTR801,TR802
and TR803 before being fed to the tube base panel. External RGB
signalsare also abletobefed intothisICon pins22,23and 24. These
pinsare normally fed withRGBlevelsof 700mVpp signals fornominal
display. The choice of display is determined by the switch pin on
IC800-(21). This is controlled by the output of the teletext chip blank
signal or the blanking signal from the microcontroller for on screen
graphics display or the PERITEL pin 8.
7.1 Auto Grey Scale Tracking
The system also incorporates an automatic grey scale tracking sys-
tem. This removes the need for manual adjustments to set up back-
ground luma levels in high-light and low-light areas on CRTs.
Forcorrecttrackingtheautogreyscaleworksontheprincipaloftaking
measurementsof the dark current during thefieldblankingperiodand
also inserting a peak white signal in that period and setting those
thresholdstocontroltheoutputstagesofthechip.Thisensuresthatthe
tube characteristics are constantly being matched by the video output
sothatgreyscaleandpicturecolourintegrityisconstantlymaintained.
7.2 Beam Limiter
The RGB output gains are also affected by the beam limiter circuit on
IC500. This is to prevent the tube from being damaged or its life
expectancy being shortened by excessive beam current.
Thesensingof the beam current is performedatthebottomendof the
DST secondary supplying the EHT focus and G2 voltages to the tube.
The reference point is pin 7 on the DST, this current is sensed as a
changeinvoltagedevelopedacrossresistorsandfedtothebeamlimit
sense IC800-(9). This voltage is measured against a reference which
represents maximum beam current. When the sensing level exceeds
the reference then the gain on RGB output amps is reduced, thereby
reducingthebeamcurrent.Saturationcontrol,brightnessandcontrast
are adjusted via the remote control but the nominal levels are preset
inthefactorybytheI2Cbususingthemicrocontrollerandtestsoftware.
8. System Microcontroller (IC500)
TheST6365 is adedicatedmicrocontrollerfor TVcontrolapplications.
Ithassuchfeaturesasdedicatedvoltagesynthesistuningcontrol,AFC
control and on-screen graphics display generator. Also it has a
dedicated infrared remote control serial data input. This microcontrol-
lerhasadedicatedI2CportforcommunicationtoothercontrollableICs.
The controller clock frequency is 8MHz and this clock speed is
achieved by connecting an 8MHz ceramic resonator across the
oscillator pins 31 and 32 with two 100pF capacitors, C507 and C508,
to ground from each pin. The timing for all functions performed by the
microcontroller including I2C bus are taken from this clock.
8.1 Voltage Synthesis
Theon-chipvoltagesynthesistuningperipheralhasbeenintegratedto
allow the generation of a tuning reference voltage. The peripheral is
composed of a 14 bit register that represents the tuning voltage at
pin 1. This voltage is generated using pulse width modulation and bit
rate multiplier techniques.
The 14 bit counter gives 16384 steps which allow a resolution of
approximately2mVoveratuningvoltagerangeof32V.Coarsetuning
isachievedbyPWMofthe7mostsignificantbitsofthe counter, whilst
fine tuning is achieved by BRM (Bit Rate Multiplication) of the 7 least
significant bits of the counter.
The resultant digital pulse train is fed into the base of TR410. This
invertsthepulsetrainwhichisthenfedintothe3stageintegratorwhich
integrates the pulse train into a DC voltage.
8.2 AFC Control
The output of the voltage synthesizer can be changed either by the
remote control or the local keyboard. The tuner oscillator is kept on
frequency by the application of AFC. The AFC acts on the voltage
synthesizervia a feedbackpath.TheAFC is generated byIC400.This
voltage is fed back to the AFC pin 9 on the controller. As the tuner
oscillator drifts either up or down so the signal applied to IC400
deviates from the optimum. As a result an error voltage appears on
IC400-(2). This voltage can be either positive or negative with respect
to the optimum voltage. This error voltage is fed to pin 9 of the
microcontroller. This voltage is then digitized. If the digital value is
optimumthennochangeismadetothesynthesizeddigits.Ifthedigital
value is either side of optimum, then the resultant AFC value is either
added to or subtracted from the synthesizer value.
8.3 Analog Controls
Pins2and5onthemicrocontrollerarePWMD-Aconverters.However,
these are only 6 bit resolution which is perfectly acceptable for the
analog functions they perform.
TheD-Aonpin2isusedastheelectronicvolumecontrolforthesound.
TheD-Aonpin3isusedforthemulti-levelvoltagecontrolforaudioand
video switching of IC400 and IC450. The D-A on pin 4 is used to
produce the threshold level for the AGC to the tuner. The final D-A on
pin5isasyetuncommitted.Themicrocontrollerhas3I/Oportsaswell
as the dedicated peripheral pins, some of the I/O ports also have
dedicated functions and are listed as their dedicated function, i.e. the
AFC on pin 9 is bit 3 of port B.
8.4 Key Pad Interface
Bits 0-2 and bits 4-5 of port B provide the matrix for the crosswire
keypad.
8.5 Sync Detector/Mute Control
Bit 6 of port B is a sense pin which mutes the sound when text is
displayedandincomingsignalis lost. Normally the microcontroller will
mute the sound when the aerial is removed or tuning is off station
because it detects no line lock coincidence.
However, in out-of-hours sync mode, the text chip set detects lack of
sync coincidence and mutes the sound. Bit 0 on port A senses the
status of pin 8 on the peri connector for switching video and sound to
incoming signals on the peri connector.
8.6 Peritel Monitor/OSG Control
Bit 1 on port A monitors the blanking signal on pin 16 of the peri
connector and also the blanking signal from text and OSD sources.
Bit 2ofportAactsasthecontrollinefortheswitchthatactsonSAW450
asdescribedinsection2.Bit3isusuallylinkedtoground, however for
System PAL BG/SECAM L/L’ this link is omitted.
8.7 Band Switching and LED Driver
Bits4to6ofportAarethebandswitchingoutputswhichdrivetheband
switches.Bit7 of port A is connected tothe LEDD500.Pins22and25
are OSG display pins whilst pins 26 and 27 are the sync input pins.
Pin33 is the hardwarepower-onreset. Pin 34 istheSECAM L/L SAW
selector switch. Pin 35 is IR input line. Pin 36 is BG/DK system select.
8.8 Standby Control/ Sound Mute
Pin37isavailableasastandbylineforexternaluse.Innormalstandby,
thecontrollershutsdownallcircuitsthatprovidedrivetooutputstages,
thereby placing the system in quiescent current consumption mode.
Pin39isthesoundmuteoutputwhichdrivesthesoundmutetransistor
TR5 and TR7. Pins 40 and 41 are the dedicated I2C bus.