Hitachi CPT2046 Schematic

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EnglEnglishsh

SAFETYSAFETY

SAFETY PRECAUTIONSSAFETY PRECAUTIONS

WARNING: The following precautions must be observed.

ALL PRODUCTS

1. Before any service is performed on the chassis an
isolation transformer should be inserted between
the power line and the product.

2. When replacing the chassis in the cabinet, ensure
all the protective devices are put back in place.

3. 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.

4. 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.

5. Always replace original spacers and maintain lead
lengths. Furthermore, where a short circuit has
occurred, replace those components that indicate
evidence of overheating.

6. Insulation resistance should not be less than 2M
ohms at 500V DC between the main poles and
any accessible metal parts.

7. 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.

8. 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

1. 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

1. 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.

2. 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).

3. 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

4. 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

LASERS

If the product contains a laser avoid direct exposure to the
beam when the cover is open or when interlocks are
defeated or have failed.

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SAFETY AND ISOLATIONSAFETY AND ISOLATION

Under no circumstances should any form of repair or
maintenance be attempted by any person other than a
competent technician or engineer. Most of the circuitry on
the chassis is isolated from the AC supply by T801, C831,
R821, IC802 and 6mm air gaps. To maintain this safety
factor ensure that, after repair, any gaps or leakage paths
are not reduced by protruding wires etc., following
component replacement

NOTE: although the output supply paths from the power
supply section are isolated from the incoming AC supply, the
bridge rectifier and the control and regulation circuits are not
isolated. Therefore, when servicing the power supply section
of the chassis, the AC supply should be connected via an
isolating transformer of at least 200 watts rating.

The power supply section remains charged with respect to
chassis for 30–60 seconds after switching off. Care should
be taken to avoid touching the power supply area of the
chassis during this time.

Components marked ! in the parts list are safety approved
types and should be replaced only with components supplied
or approved by our Service Department. It is also
recommended that components not marked with the safety

symbol should be replaced with parts of the type originally
fitted. This applies particularly to those resistors which are
‘stood off’ the printed circuit boards.

Chassis Operation and Alignment

The majority of chassis functions are implemented within
IC504 and its associated circuitry. These are controlled by
the micro-controller IC701 via the I²C bus, a two wire bus
(SDA, Serial Data and SCL, Serial Clock). The micro­controller contains twenty adjustable parameters between
00–13 (hex) which are used to control the functions of IC504
. (SeeAdjustments for further details on how to adjust or reset

these.)

Handling Precautions - Static Electrical Charge

The receiver contains devices which may be damaged by
static electrical charges during handling. To avoid damage,
soldering irons should be earthed, and service personnel
should, ideally, wear wrist straps earthed through a 1M ohm
resistor. If the latter is not practical, they should discharge
themselves by touching an earthed point. Sensitive static
devices should be packed in suitable conductive containers.

IMPORTANT: although the receiver chassis is isolated, the
AC supply should be disconnected during service
replacement of such static devices.

When the mute condition exists, 01572 will be turned on
due to pin 27 of ICI501 going low. LED1572 is thus

illuminated for as long as the set is held in the mute

condition. ICI 501 is powered at pin 28 by the

supply
obtained from the citac board
ICI 502 type PCD8571 is the battery backed memory IC. It
is controlled by clock and data commands from 501,
storing information during the search and setting up
procedure and releasing the information upon command
thereafter. For programme selection ICI502 will store a
digital number relating to frequency and for brightness,
colour, contrast etc it will store analogue values. These
analogue values will be common to all programmes.
Clock signals are fed into pin 6 and data information is fed
in or sent out from pin 5.
BA TT15 01 the battery is a nickel cadmium
rechargeable cell which is trickle charged at about

while the TV is working. When the battery is new and fully
charged, it should provide back-up for the memory

for approx 1 year without further charge.
ICI 503 type SAA1 061 is the seven segment display driver.
It is driven by the

supply at pin 6 and the signals at pins
5, 8 and 9. Pin 5 is supplied with a square wave for the
entire duration of the data. Pin 9 is the clock input and pin 8
is the serial data, controlling which of the segment displays
or dots are turned on.

because the tuning will revert to the stored value when the
signal disappears and doing a programme selection
initiate a search of the channel spectrum again.

SEARCH TUNING

This is achieved by micro stepping through each channel
spectrum in ascending numerical order commencing with
the channel already tuned under the programme number
selected.

BOARD PC204 (Computer interface,

tuning and analogue control)

This assembly generates the and supplies. The

is obtained via the full bridge rectifier and

ICI401 type

7805H. It is fused by an 800mA fuse

smoothed by Cl404 and is used to power the

micro processor board. The

supply is obtained from

the full bridge rectifier

and type

It is smoothed by fused by

500mA and powers the Amp.

Pressing the search button causes the tuning to advance
to the next micro step which upsets the status quo
conditions for having a correctly tuned signal. The tuning
will then continue to increment upwards in micro steps
changing the displayed channel number as the channel
boundaries are crossed. Each micro step is set by
reference to the ROM in ICI 501 and when achievedwithin

a “F-Lock” is set. The AFC is then switched in and
signal induced variations are monitored. If a carrier is
present within the micro step “F-Lock” will remain and a
check is made to detect the presence of a ‘stop” signal on
pin 7 of If a carrier is not present the AFC voltage

will be determined by the ratio of

on the main

chassis

and will signify the absence of a valid

carrier, wherupon the “F-Lock” is cleared.

If the carrier is a the sync pulses fed to Q1412 will

cause 01413 to turn off at line frequency and allow line

pulses through to the intergrating capacitor Cl 415.

This causes a “stop” signal of about

to appear on pin 7

A combination of “F-Lock” and the high “stop”
signal signifies that a TV signal has been tuned, hence the
search routine is halted. If it is a standard BBC or ITN
transmission the tuning should be stored without ATC. All
other signal sources should be stored with ATC on.
Acceptance of the store command is signalled by an
audible “bleep” which is output from pin 6

SECURITY OPTION LINK

type SAB3037 is powered by the from the

If this link is connected, programme information on Nos

main chassis and it controls all analogue and tuning

6 can only be stored by pressing the hold button on the

functions with facilities for AV switching. All these

handset first, then pressing the store button on the front

functions are controlled by clock and data information fed

control panel within 4 seconds. This method prevents any

from ICI501 or ICI502 into pins 2 and 3 Bus)

accidental removal of the stored programmes by the

integrated circuit bus.

customer.

X1401 is a crystal and this is used as the main
refe rence frequen cy fo r cal culating channel and
programme frequencies. The is utilised to create an
accurate timing window for counting pulses from the
prescaler in the UHF tuner.

DIRECT TUNING

ANALOGUE CONTROLS

This is accomplished by pressing the key followed
by the transmitter channel number. The oscillator
frequency of the tuner is divided by 256 and fed to pin 20 of
ICI403 as the prescaler. Here it is compared to the
required frequency which is output from the ROM in

Any difference causes ICI403 to alter its voltage
output to the tuner until equality is achieved.
If there is no transmission on that channel, the system will

automatically search through the chosen channel
spectrum

to look for off frequency transmissions.
If none are found the tuning will return to the
frequency. Therefore receivers can be accurately tuned to

channels in the absence of a signal.

The channel spectrum of

is divided into 6 equal parts
called micro steps and if an off frequency transmission is
present the system will stop tuning at the center
frequency of the nearest to correct micro step. In this case

the ATC circuit should also be activated; the ATC indicator
will now be illuminated. The tuning will then be corrected
by AFC action and the offset stored in the programme
memory when the store button is pressed. Should the
offset transmission drift in frequency, the tuning circuit will
track with the drift.
Note that if the drift is unusually large or the signal is
interrupted by any means, it may be necessary to select
the programme number again to restore the picture. This is

The voltages at pins 1, 22, 23, 24 of ICI 403 are adjustable
between approx by the local keyboard
commands for brightness, colour, volume and contrast.

Except for contrast, these functions are also controlled by
the handset. Instructions to increment or decrement the
analogue controls are passed via the IC2 Bus. During
installation a “normal” setting should be stored which will
always be recalled at switch on, or by the “normal”
command on the handset. Note the volume output will not
be affected by the “normal” command.

OPERATION

Upon selecting programme 17, 18 or 19, one of the pins

14, 15, 16 will go low. This is applied to the AV board PC222
and will illuminate the AV diode on PC202 and cut off the
sound/vision if stages etc as described in the AV circuit
description.

MAINS INTERRUPTION STAGE

01454 is a mains interruption circuit and operates in the

following manner. Should a brief mains interruption occur,
during the short time the receiver is off, the set may reset
to programme No. 1 or when applicable from teletext to TV
mode. To prevent this happening is operated by the

supply from the main chassis When an

interruption occurs the

supply will disappear
immediately. However the from PC205 will fall slowly
thus 01454 will still conduct and maintain

at its emitter
for a brief period. This ensures that the supply to the
micro processor is maintained for the short time the mains
supply is off, thus holding the IC in the same mode of
operation

the supply returns.