Service manual
CHASSIS 2112-Series EC7-A
12
The used high voltage transformer (T650) is Slot technology and it does not incorporate bleeder (internal resistance
to unload the MAT).
4.3.3 Width
adjustment.
In this chassis the width adjustment only exists as forecast in the printed circuit and in the control software; but it is
not mounted but it is optional (maybe it does not appear on the scheme).
The width adjustment is totally different from the used one until now in 90º deflections, width adjustment coil or
110º; stage E/W. The adjustment is made from the Service Menu, changing the H.AMPL. value. The
microprocessor generates a PWM signal with a duty cycle proportional to the value of H.AMPL. registry. Q654,
C658, C659, D653, Q653, Q652 and D654 compose the circuit that allows the adjustment, it modifies the voltage
wave form at the central point of the diode modulator producing a change width of picture.
4.3.4
H_FLY&SYNC signal generation.
This signal is used to achieve the horizontal synchronisation
.
The microprocessor uses it to synchronise the RGB
insertion and the video processor for the RGB blanking and as PHI-2PLL input.
It is generated from the main flyback with AC coupling. There are some pulses in Q651 transmitter, with line
frequency and synchronized with the main flyback, with a width of 8V.
4.3.5
Recovered line voltages.
From the flyback transformer (T650) some supply voltages are extracted:
#
±
12 V, used by the vertical amplifier and by the driver stage.
#
B3 (130 V), used by final RGB amplifiers.
#
Heaters.
4.3.5.1 Heater
supply.
The T650 voltage and the R573 value determine the heater supply voltage. In order to maintain the heater supply
within right limits, the B1 adjustment (line supply) must be as the specified one, and both deflection values and
R573 must be as the specified ones. A heater supply voltage excessively high, it reduces considerately the tube life.
In case of measuring the heater supply voltage, it must be done by a special voltmeter that has to accomplish the
following characteristics: minimum crest factor of 10 and minimum bandwidth of 5MHz. Portable multimeters hardly
fulfil these characteristics.
4.3.6 EHT
discharge.
The EHT discharge is carried out by means of the following procedure: before switching off the TV set, the
microprocessor sets to 1 a bit in video processor (IC400) by means of I2C bus. These bit provokes that the video
processor duplicates the line frequency for 160 mS at the same time it moves the RGB outputs to white.
The result: the flyback height cuts by half when the line frequency is duplicated, it provokes that the line transformer
(T650) generates an EHT of half the normal working value, approximately. When the current beam conducts (RGB
outputs are white), there is EHT consumption, what causes the descent from its normal working value to something
less than half. A complete EHT discharge is not carried out; therefore it has to be totally discharged before
removing the EHT vent
.
There are two visual aspects of EHT discharge (eligible by OSO from Service menu):
#
Discharging when the vertical deflection circuit is working: A white narrow strip with retrace lines is observed.
#
Discharging when the vertical deflection circuit is diverted upwards: a while halo is observed in the top of the
screen.
In case of switching off the switch (or removing the mains), the circuit that generates –PD signal (formed by Q855
and its periphery) advises, in advance, that the microprocessor
is going to remove the mains. It remains a while of
working before the source stop oscillating (due to energy stored in C803). This while is enough to the
microprocessor carries out the procedure of switch off and discharge of EHT.
4.3.7 Protections.
The protection of horizontal deflection is enabled when –DEFL_FAIL (pin 14 of IC100) has a low level. The
microprocessor reads this signal value and, in this case, it sets the TV in ERROR_3.
The protection of horizontal deflection is disabled in these cases:
#
I2C BUS STOP is chosen in service mode.
#
The TV set is in Stand-By mode.
#
During the switch on /off transients of the TV set.
#
In forced switch on mode.
4.3.7.1
Low Flyback protection.
If there is a flyback too low (it happens when the deflection coil
path is opened or when there is an internal short-circuit
in T650), D561 stops conducting and, therefore, –DEFL_FAIL signal resets to low level.
4.3.7.2
Heater short-circuit protection.
If there is a heater short-circuit, D561 stops conducting and, therefore, –DEFL_FAIL resets to low level.
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