CAUTION:
Before servicing this chassis, it is important that the service technician read the "Safety
Precautions" and "Product Safety Notices" in this service manual.
ATTENTION:
Avant d'effectuer l'entretien du châassis, le technicien doit lire les «Précautions de sécurité»
et les «Notices de sécurité du produit» présentés dans le présent manuel.
VORSICHT:
Vor Öffnen des Gehäuses hat der Service-Ingenieur die ,,Sicherheitshinweise" und ,,Hinweise
zur Produktsicherheit" in diesem Wartungshandbuch zu lesen.
SERVICE MANUAL
MANUEL D'ENTRETIEN
WARTUNGSHANDBUCH
Data
contained
within
this
Service
manual is subject to alteration for
improvement.
Les données fournies dans le présent
manuel d'entretien peuvent faire l'objet
de modifications en vue de perfectionner
le produit.
Die
in
diesem
Wartungshandbuch
enthaltenen Spezifikationen können sich
zwecks Verbesserungen ändern.
SPECIFICATIONS AND PARTS ARE SUBJECT TO CHANGE FOR IMPROVEMENT
COLOUR TELEVISION
DECEMBER 1999
SM00025
C28WF523N
C32WF523N
C32WF720N
C32WF727N
C32WF810N
C36WF810N
C36WF830N
CL28WF720AN
CL32WF720AN
CL32WF720AND
CL32WF727N
CL32WF810AN
CL36WF810AN
CL36WF830AN
D36WF840N
SAFETY PRECAUTIONS
WARNING: The following precautions must be observed.
ALL PRODUCTS
Before any service is performed on the chassis an isolation transformer should be inserted between the power line and the
product.
When replacing the chassis in the cabinet, ensure all the protective devices are put back in place.
When service is required, observe the original lead dressing. Extra precaution should be taken to ensure correct lead dressing
in any high voltage circuitry area.
Many electrical and mechanical parts in HITACHI products have special safety related characteristics. These characteristics
are often not evident from visual inspection, nor can the protection afforded by them necessarily be obtained by using
replacement components rated for higher voltage, wattage, etc. Replacement parts which have these special safety
characteristics are identified by marking with a
on the schematics and the replacement parts list.
The use of a substitute replacement component that does not have the same safety characteristics as the HITACHI
recommended replacement one, shown in the parts list, may create electrical shock, fire, X-radiation, or other hazards.
Always replace original spacers and maintain lead lengths. Furthermore, where a short circuit has occurred, replace those
components that indicate evidence of overheating.
Insulation resistance should not be less than 2M
at 500V DC between the main poles and any accessible metal parts.
No flashover or breakdown should occur during the dielectric strength test, applying 3KV AC or 4.25KV DC for two seconds
between the main poles and accessible metal parts.
Before returning a serviced product to the customer, the service technician must thoroughly test the unit to be certain that it is
completely safe to operate without danger of electrical shock. The service technician must make sure that no protective device
built into the instrument by the manufacturer has become defective, or inadvertently damaged during servicing.
CE MARK
HITACHI products may contain the CE mark on the rating plate indicating that the product contains parts that have been
specifically approved to provide electromagnetic compatibility to designated levels.
When replacing any part in this product, please use only the correct part itemised in the parts list to ensure this standard is
maintained, and take care to replace lead dressing to its original state, as this can have a bearing on the electromagnetic
radiation/immunity.
PICTURE TUBE
The line output stage can develop voltages in excess of 25KV; if the E.H.T. cap is required to be removed, discharge the
anode to chassis via a high value resistor, prior to its removal from the picture tube.
High voltage should always be kept at the rated value of the chassis and no higher. Operating at higher voltages may cause a
failure of the picture tube or high voltage supply, and also, under certain circumstances could produce X-radiation levels
moderately in excess of design levels. The high voltage must not, under any circumstances, exceed 29KV on the chassis
(except for projection Televisions).
The primary source of X-radiation in the product is the picture tube. The picture tube utilised for the above mentioned function
in this chassis is specially constructed to limit X-radiation. For continued X-radiation protection, replace tube with the same
type as the original HITACHI approved type.
Keep the picture tube away from the body while handling. Do not install, remove, or handle the picture tube in any manner
unless shatterproof goggles are worn. People not so equipped should be kept away while picture tubes are handled.
SM00025 Service Manual
TABLE OF CONTENTS
1
DESCRIPTION ................................................................................................................................................... 1
1.1
A8/D8 MKII MAIN PSU ................................................................................................................................ 1
1.2
DTI PSU....................................................................................................................................................... 2
1.3
SCAN VELOCITY MODULATION............................................................................................................... 3
1.4
DIGITAL DOUBLE-SCAN CONVERSION UNIT (FEATURE BOX) ............................................................ 3
1.5
INPUT PROCESSOR (TDA 9320) .............................................................................................................. 4
1.6
PICTURE IMPROVEMENT (TDA9178) ...................................................................................................... 5
1.7
TUNER......................................................................................................................................................... 5
1.8
RGB PROCESSOR (TDA9330) .................................................................................................................. 6
1.9
SIGNAL PATH DESCRIPTION ................................................................................................................... 7
1.10
AUDIO CIRCUIT ...................................................................................................................................... 7
1.11
DOLBY DECODER (Prologic Models)..................................................................................................... 8
1.12
DIGITAL AUDIO ....................................................................................................................................... 8
1.13
AUDIO AMPLIFIER................................................................................................................................ 10
1.14
DEFLECTION ........................................................................................................................................ 14
1.15
MICRO-CONTROLLER SECTION ........................................................................................................14
1.16
MULTIPICTURE FUNCTION ................................................................................................................. 22
1.17
AUTOWIDESCREEN............................................................................................................................. 23
2
SERVICE .......................................................................................................................................................... 24
2.1
BOARD ADJUSTMEMT ............................................................................................................................ 24
2.2
FINAL ALIGNMENT (by Software) ............................................................................................................ 27
2.3
AUDIO SUB BOARDS............................................................................................................................... 29
2.4
SHIPPING SPEC DATA SHEETS............................................................................................................. 32
3
SCHEMATIC DIAGRAMS................................................................................................................................. 37
4
PCB LAYOUT DIAGRAMS ...............................................................................................................................
47
5
PARTS LIST......................................................................................................................................................
57
SM00025 Service Manual
1
1 DESCRIPTION
1.1 A8/D8 MKII MAIN PSU
From switch on the AC voltage is rectified by the
bridge D900 which produces approximately 300V
across C918. This is then applied to the collector of
Q903 via the primary winding of T900. Initially the
voltage on pin 7 of I900 will rise to approximately
16V via R901, D929 and Q905. This allows the
internal circuitry of IC900 to generate a sawtooth
waveform at pin 4, from which a square wave output
is obtained at pin 6. This output is applied to the gate
of Q901 which turns on and off, this alters the
voltage on the emitter of Q903 causing this device to
turn on and off, generating the outputs in the
secondary windings of T900.
After initial power up of I900 pin 7 is supplied from
the bias winding (pin 18) of T900 via D911 for
continued operation. The bias winding voltage is also
rectified by D922 which is then supplied to the base
of Q905 low via R908/Q906/R924 turning Q905 off,
this is done to reduce the power dissipated by R901
once the power supply is running.
A current sense circuit consisting of R910, R939,
R922 and R980 feeds back a voltage to pin 3 of
I900, MAX voltage approximately 0.8V. Should the
applied voltage exceed the reference the pulse width
is limited from output pin 6. In this way Q903 is
offered protection from changes in primary current.
R909 and C914 act as a soft start circuit, this limits
the pulse width output from pin 6 during the initial
start up period, allowing a gradual rise to full power.
Q909, R918 and associated circuitry are for reducing
the frequency of the power supply when the set is in
standby. A sense voltage rectified by D922
consisting of R905 and R906, supplied pin 2 of I900,
this is then compared to an internal reference
voltage. If it exceeds the internal reference the
output from pin 6 will be limited by the internal error
amp. The secondary voltage induced in T900
winding 7/9 is rectified by D950, producing the HT
voltage which is smoothed by C977. In standby the
HT rises slightly.
Winding 5/10 produces approximately 10V via D951,
which is smoothed by C957. This is then applied to
dual DC-DC converters (+8V, +5V out). A control
ramp is found on pin 2/6 I900. This ramp is formed
by R944/C935, and terminated by Z913, D902, R934
network. Ramp frequency is clamped to the main
PSU frequency by the winding on pin 5 T900. This
ramp is compared with the feedback level from I902
(+5V) I904 (+8V). The reference device monitors the
output and changes the DC level to pin 5. The ramp
crosses the DC feedback level, and the output at
pins 1/7 goes low. The output at pins 1/7 starts high
at the beginning of the ramp, goes low at ramp cross
level. This action via Q912, Q911 controls the pulse
width and so the regulation of the +8V/ +5V rails.
The output pulse width changes with load to
maintain the correct regulating voltage.
The output of I910 pins 1,7 are buffered to improve
switching losses using a push - pull transistor
network Q918, Q917 (for +5V). This transistor
network gives fast edge switching of Q912 (+5V) and
Q911 (+8V). Over current protection is provided with
the current sense resistor RP03. Network Q956
RP04/C966 pull pin 10 of I903 high if high load
current is flowing through RP03.
Winding 2/11 produces approximately 16V via D952,
which is smoothed by C955 and then applied to
Q921 through R974, which is used as a current
sense. The output from Q921 supplies 16V for the
audio amplifier I401.
HT regulation is controlled by Q954 stage. The base
of Q954 is set at a pre-determined level by the
resistor network R950, R982 and R953. The emitter
of Q954 is held at approximately 6.2V by Z950.
Should the HT rise, the base voltage becomes more
positive than the emitter, and this difference is
amplified by the transistor and applied to optocoupler
I901. The output from I901 is then applied to pin 1 of
I900 which regulates the HT by altering the duty
cycle of the waveform output from pin 6 of I900.
1.1.1
STANDBY SWITCHING
The low voltage supplies are switched off in standby,
this is controlled by the micro processor which
outputs a high in standby and a low when the set is
out of standby. This is then applied to resistors R923
and R940/R977. This `high' is also applied to the
base of Q915, Q916, Q910 which in turn terminate
operation of the +8V, +5V DC-DC converters, and
pull the gate of Q921 low so switching the +16V
audio supply to low state. In standby the +B voltage
rises slightly to maintain bias winding voltage to pin 7
of I900. To switch the set out of standby the on/off
line is switched high by the micro, and Q916, Q915,
Q910 are deactivated, causing the +8V, +5V, +16V
rails to return to normal operation.
1.1.2
POWER GOOD AND PROTECTION
I903 is made up of 4 comparators, the power good
line uses comparator 2. Pin 5 is used as the
reference which is held at 2.5V by I905 supplied by
pull up resistor R968. Pin 4 uses R961/R962 and
R955/R959 as a potential divider which is connected
between the +10V and T900 winding through D959
which is in forward converter mode. In operation this
SM00025 Service Manual
2
means pin 4 is held below the reference level of pin
5 until the mains supply is interrupted or the set is
switched off at which time pin 4 rises above pin 5
and the output pin 2 is pulled low. This low is sensed
by the micro. In normal operation pin 2 is held high
by pull up resistor R990 from the 5V supply.
The protection line (pin 14) is held high under normal
running conditions by R971 from the 5V supply, this
high is applied to the protection line to the micro.
When the protection line is pulled low the set goes
into standby mode, the set can be restarted by the
usual methods of bringing the set out of standby, but
until the cause of the protection circuit operation is
removed the set will return to its standby state.
The over current for the 16V audio supply uses
comparator 1, a reference voltage is set up on pin 6
by resistors R967, and R964. The voltage being
compared is fed to pin 7 using the potential divider
R968 and R966 which is supplied from the output
side of the current sense resistor R974. Should the
voltage on pin 7 fall below that of pin 6, pin 1 will be
pulled low, thus pulling the protection line low via
D958 putting the set into standby.
Comparator 3 is used to protect against a layer short
within the FBT, it will also act as protection for a
short on the secondary outputs of the FBT. I903 is
supplied with approximately 16V via D960 to pin 3,
from this supply a reference voltage is fed to pin 9
using potential divider R972/R969, fed via Z948
supply. Pin 8 is supplied by another potential divider
this time made up of three resistors R973/R970 and
R760 samples the current flowing through Q752,
should this increase, the voltage drop across R760
will increase and raise the voltage of pin 8, when it
exceeds pin 9, pin 14 will be pulled low, putting the
set into standby.
Comparator 4 is used for EHT/over voltage
protection, as all the FBT secondary voltages are
proportional, the 200V supply to the CRT base is
used to generate the voltage to be used in
comparison, this is done by using a potential divider
made up of R718, R749 and R719. Z708 monitors
the voltage at the junction of R718 and R749, if this
exceeds 36V, the Zener diode conducts, applying a
high on pin 10 of I903, this is compared with the
reference voltage on pin 11, which also uses the
2.5V set up by I905. When pin 10 is higher than
2.5V, pin 13 is pulled low, in turn pulling the
protection line low via D957, putting the set into
standby.
The LT lines are given protection using diodes D931,
D932 and D930, these are connected in reverse bias
from the prot sense line to the 8V and 5V. The +5V
standby link is protected by D986, pulling the
reference Z950 low if a short is seen on the output of
I952. The +16V phono out has a diode back to I903
pin 5 in case of short.
If the +B or audio supply lines become short circuit
to ground before the protection on the secondary of
the power supply, the primary over current protection
(I900 pin 3) will operate, turning off the drive output
from I900 pin 6. A latch circuit
Q955/R998/RP01/C964, will operate to turn the
power supply into standby (under fault condition) if
the software fails to act on I903 pin 14 low. Delay
before latch set by C964/R994. The +B is given
protection from overvoltage via Z907, Z907 goes
short circuit if the +B voltage rises above 180V DC.
1.2 DTI PSU
1.2.1
CIRCUIT DESCRIPTION
The mains is switched on via the {TV on}. At this
point the AC mains is rectified by D9019, D9001,
D9002, D9003 which produces approximately 340v
DC across C9026. This is then applied to the
collector of Q9000 via the primary winding of T9000.
Initially the voltage on pin 7 of I9000 will rise to
approximately 16v via R9001, D9000, this allows the
internal circuitry of I9000 to generate a sawtooth
waveform at pin 4 from which a square wave output
is obtained at pin 6. This output is applied to the gate
of Q9005 turning the MOSFET on and off, pulling the
base/emitter high and low accordingly reducing
cross over, generating the outputs in the secondary
windings of T9000.
After initial power up pin 7 of I9000 is supplied from
the bias winding pin 3 of T9000 via D9010 for
continued operation hence R9001 unable to provide
running current demand for I9000 [200mA approx].
A current sense circuit consisting of R9057, R9013
and R9015 feeds back a voltage to pin 3 of I9000,
this voltage is compared with an internal reference
voltage of approximately 0.8V, should the applied
exceed the reference, the pulse width is limited from
output pin 6 [chip in over current mode]. In this way
Q9005 is offered protection from changes in primary
current. Secondary overvoltage protection is offered
also by R9009, should the feedback be disabled
then the secondary voltage will be limited to safe
levels, the output from pin 6 will be limited by the
internal error amplifier and internal reference.
R9006 and C9010 act as a soft start circuit, this
limits the pulse width output from pin 6 during the
initial start up period, allowing a gradual rise to full
power. ZD9000 and ZD9001, ZD9006 will go short if
Q9000 should go short, protecting I9000 and Q9005.