Circuit Description; Fault Monitoring; Vertical Deflection - Grundig TVR 3735 FR/TOP Servicehandbuch

Description
Description
1. Power Chassis (PS)
1.1 Power Chassis – Power Supply
Construction of the Power Supply
The power supply consists of 2 separately working blocking-oscillator
type converters (Standby Power Supply Unit and Mains Power Supply
Unit).
– The Standby Power Supply Unit (I807 / T802) supplies the two
processors I701 and IN01 of the Signal Chassis with the voltage
ENVR 6V.
– The Mains Power Supply Unit (I802 / T801) supplies all other
components of the Power and Signal Chassis of the product. It is
switched on by a HIGH level at IN01-(55) of the Signal Electronics
via plug contact P805-(10), Q803 and the relay RLY1.
The following description refers to the Mains Power Supply Unit.
Principle of the Blocking Oscillator-type Converter
During the conducting phase of the switching transistor Tr1 in I801
energy is transferred from the mains to the transformer. This energy is
fed out to the load during the phase the transistor is switched off. By
means of the switch-on period and the frequency the energy transfer
during each cycle is so controlled that the output voltages are inde-
pendent of changes in the load or the input voltage. Controlling and
driving is effected by I801.

Circuit Description

The mains voltage is rectified by the bridge rectifier D801...D804 and
filtered by C819. L801 is provided to protect the power supply against
interfering pulses from the mains. During the starting phase the power
for I801 is supplied to Pin 9 via R804 and C817. After the starting phase
the power is obtained from the transformer winding 6 / 5 and D808.
The base of the switching transistor Tr1 in I801 is driven via the driver
Tr2 within I801 and Pins 8, 4, 3. During the conducting period of the
switching transistor Tr1 in the I801 the current of the rectified mains
voltage flows through the primary winding of the transformer (contacts
2 / 4), I801-(1 / 2) and R817 to ground (in the primary side). Since the
voltage at contact 2 of the transformer is almost constant, the current
rises linearly. The intensity of this current depends on the mains
voltage and the inductance of the primary winding. In the transformer,
a magnetic field develops which corresponds to a certain amount of
energy. During this phase, the diodes are cut off due to the polarity of
the secondary voltages. As soon as the switching transistor Tr1 is
switched off the energy transfer to the transformer is stopped. The
energy accumulated in the transformer is now transferred to the
secondary windings. Due to the fact that the polarities of the voltages
are reversed by the transformer, current flows through the secondary
windings of the transformer, through the diodes, electrolytic capacitors
into the load.
When the total amount of energy stored in the transformer has been
transferred to the load and no magnetic field is left in the transformer,
the voltages at the secondary windings fall below 0V. These zero
passages are detected by I801 at Pin 5. The transistor Tr1 is switched
on again and the next cycle is started.
Control of the switched mode power supply is effected by varying the
frequency and the conducting phase of the switching transistor to the
effect that the energy transferred from the mains to the transformer is
increased or reduced. The control information is obtained from the
transformer winding 7 / 5 and is taken via D808 / C817 to Pin 7 of I801.
The maximum power possible to be taken from the secondary side is
determined by R817.
From the secondary side, the voltages (SW 6V, SW 12V, S B+, MO B+
and 123V) are available which are rectified and filtered by the respec-
tive components (diodes / capacitors / chokes). The 123V voltage for
generating the high voltage is switchable by a LOW level at processor
I701-(43) of the Signal Electronics via QC705, plug contact P406-(1),
Q403 and RLY2

Fault Monitoring

At a voltage of V <5V and >11V at Pin 9 of I801 the output stage is
in
switched off.
For monitoring the primary current (I
representing the primary current is fed to Pin 5 of I801 via the resistors
R817 and R834. If this voltage exceeds -1V, the switching transistor
Tr1 in I801 is switched off. This process is repeated whenever the
switching transistor Tr1 is switched on. The transformer winding 6 / 5
and D810 at I801-(6) is responsible for detecting an overvoltage and
2 - 6
of Tr1 in I801) a voltage
E
undervoltage condition at the secondary. The drive to the integrated
oscillator is stopped at a level of typically 0.75V and 5V. The oscillator
is active at about 1.4V.
Additionally, the transformer winding 6 / 5 and D810 at I801-(6) are
used for overvoltage and undervoltage detection at the secondary
side.
I801 is fitted with an excess-temperature sensor (TSD) for blocking the
logic if the permissible chip temperature is exceeded (typ. 150
the temperature has fallen a new start-up is possible by re-connecting
the TVR to the mains.
1.2 Power Chassis – High Voltage Section
The high voltage section is driven by the TV Signal Electronics on the
Signal Chassis. It contains the TV-I501 with the following circuit stages
for generating the drive signals:
– Sync pulse separation
– Horizontal oscillator
– Phase comparison between the horizontal oscillator and the line
flyback pulse
– Vertical oscillator
– Phase comparison between the vertical oscillator and the field
flyback pulse
Horizontal Deflection
The horizontal oscillator within I501 feeds out the "H
signal on pin 40 which is then taken via plug contact P406-(3) to the
horizontal deflection stage. This horizontal deflection consists of the
driver stage (Q401 / transformer T401), the horizontal output stage
(Q402), the horizontal deflection unit and the line transformer (T402).
The horizontal deflection unit is made up of the deflection coils, the
forward scan capacitor "S-correction capacitor" (C415) and the flyback
capacitors (C406 / C416). Current flows through the diode, integrated
in the line transistor, during the first half of scan (the electron beam
moves from the left edge to the middle of the screen), and the transistor
is switched on during the second half period of scan (from the middle
to the right edge of the screen). During the line flyback period, the line
transistor and the diode integrated in it are not conducting. The forward
scan and flyback capacitors are now in series. The resonant frequency
is increased and consequently the flyback speed as well (typ. t = 12≤ s).
The horizontal linearity (S-correction) is determined by the forward
scan capacitor C415 and the linearity coil L404. Line tearing, a typical
symptom occurring at the cross-over points in a grid pattern test picture
in high beam current condition, is reduced by C410 / D402 / R418.
The horizontal flyback pulse (SC) is fed for phase comparison through
R412 / C412 / R413, plug contact P406-(5) and R564 to the Signal
Chassis - TV Signal Electronics I501-(41).
EHT Generation
The 123V voltage supply for EHT generation is switchable via the
RLY2 relay. The relay is supplied with a HIGH level via I701-(9), plug
contact P406-(6) and I808-(4) and is actuated by a LOW level at
I701-(43) via QC705, plug contact P406-(1) and Q403.
When the line transistor Q402 is conducting, the line output trans-
former T402 is charged up. In this way, the high voltage for the picture
tube is produced during the non-conducting period of Q402. The line
output transformer is also used to obtain the necessary voltages for
focusing, brightness, cathode heating, the RGB output stage and the

vertical deflection.

Beam Current Limiting
The voltage drop (ABL) at the low-end capacitor C418 is used for
determining the average beam current. For this function, the BCI
voltage is fed through plug contact P406-(4) to the TV Signal Electron-
ics (Signal Chassis). Together with the diode D502 located there the
BCI voltage is used to reduce the contrast setting when the beam
current is too high, and to control the vertical picture amplitude.
Vertical Deflection
The vertical oscillator within I501 feeds out the deflection voltages
"V.DRI+" at pin 46 and "V.DRI-" at Pin 47. These voltages are applied
to the vertical output stage I301-(2 / 1) via plug contact P405-(4 / 3).
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out
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