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Circuit Descriptions, Abbreviation List, and IC Data Sheets
voltage generator), coupled by the HVG capacitor and then
connected to the tube's focus electrode.
Misc. components:
•
2903: Coupling vertical parabola to 7901.
•
3904/2910/3900/2904: Filtering and reshape vertical
parabola.
•
3905: Current biasing of 7901.
•
3903: Pull up and amplification resistor of 7901.
•
3909/2902/3902: Preventing focus flash going to 7901.
•
5901: Coupling and amplifying of horizontal parabola.
•
2901/3901: Coupling horizontal parabola.
9.3.4
Six Pack HVG and Beam Current
Note: Description below refers to diagram E4 (right upper part).
Different from direct view CRT, PTV is using a separated high
voltage generator for picture tube's EHT. The purpose of this is
to have a well regulated EHT and so eliminated breathing and
geometry concern. With a well-regulated EHT, the picture size
will not be modulated by the EHT variation and a stable picture
without breathing can be obtained ideally.
Somehow, due to the non-ideal regulation of the HVG in use,
HDPTV2K6 shows some breathing defect.
Other than regulated EHT, the HVG also provide -200V for
protection and +330V for dynamic focus.
A control pin is available which function as "On/Off" control by
HVG-ON signal. HVG is supplied by 130VH.
HVG output:
•
EHT info and beam limit: HVG pin2. The beam current that
being supplied to EHT is drawn from this pin. Through the
resistor 3911/3912 and capacitor 2913, we can obtain a
voltage with level and ripple proportional to beam level and
EHT ripple respectively. The voltage is buffered by 7903
and supply to HOP IC named as auto beam current (ABL).
ABL is to limit the beam current at max 1.8mA fixed by
3911/3912. This voltage goes to HOP BCL pin and HOP
will control the Contrast and Brightness depending on
software setting. Corresponding to the voltage level, HOP
IC will increase or decrease Contrast or Brightness
accordingly and so set the max. beam at 1.8mA.
•
-200V/+330V: HVG pin4, rectified by 6917/2920 and
protected by 3908. -200V is used for protection control.
Any fault causing HVG "off" will make -200V not available
and shut down the set with error code 61. +330V is derived
by negative rectification and supply to dynamic focus
circuit.
•
Test pin: HVG pin7. Applying voltage of 2V - 7V will make
HVG EHT increase and could trigger the HVG internal
protection circuit to shut down HVG.
•
HVG-ON: HVG pin8. "High" turn "on" HVG and "low" turn
"off" HVG.
Misc. components:
6903/6904/3923/3936/3924/3937/2911/6905: ABL
components for peaking and transient beam current
performance.
2926/3922/6919/3925/3921/2927: To improve the breathing
caused by the non-ideal EHT regulation of HVG. These block
of components takes the EHTinfo and input to EW correction
drive (also as DM-INPUT, diode modulator). The injected
EHTinfo will modulate the deflection current and so the
scanning size.
Beam current protection
If the picture beam current is exceeding 1.8 mA a lot, the
emitter of 7903 will be pulled "low" dramatically and will finally
turn "on" 6912. 6912 will then latch transistor 7905 and 7904
that will pulled HVG-ON "low" and disable HVG operation.
EBJ1.0U
Consequently, -200V will not be available and set shut down
with error 61.
9.3.5
Protection
Note: Description below refers to diagram E3 (left lower part).
Vertical Protection
The flyback generator vertical pulse from 7811 is injected to
7808 and turn "off" 7808 during scanning period. During flyback
period, the pulse is at "high" level and turns "on" 7808, through
7906 and 7812. It will cause G1 to be -200V and the video is
blanked.
During fault condition where vertical pulse is not available, in
addition to G1 being pulled to -20V to blank video, 7808 will be
turned "on" and so 7814 will be "off". This will cause HVG-ON
to be "low" and the set will be shut down with error 61.
Power Protect
The voltage divider 3578 and 3579 detect 5552 secondary and
input to 7557. If there is a power failure, 7557 will then be "off"
and pin1 become "high" instead of 2.5V, the voltage divider
3581/3582 will then derive a higher PROTECT signal which will
turn "on" 7809 and cause HVG-ON "low". HVG will be turned
"off" and set shut down with error 61. PROTECT is "low" during
normal operation.
Neg-Horiz-Pulse
Neg-Horiz-Pulse is derived from filament flyback phase. It is
then rectified by 6822/2840 and connected to the base of 7810
through 3847. 3847/3848 and 3861 determine 7810 base
voltage. Fault conditions cause the flyback pulse smaller will
make 7810 base more positive and turn "on" 7810. This will turn
"off" 7814 and disable HVG and cause set shut down with error
61.
+200V Protection
If +200V is not available due to some fault condition, 6812/6816
will be "off" and so is 7814. This will turn "off" HVG and set shut
down with error 61.
+15V Protection
If +15V is not available due to some fault condition, 7814 will
not be able to make HVG-ON "high" and HVG will be turn "off".
This will shut down the set with error 61.
Beam Current Protection
If the picture beam current is exceeding 1.8 mA a lot, the
emitter of 7903 will be pulled "low" dramatically and will finally
turn "on" 6912. 6912 will then latch transistor 7905 and 7904
that will pulled HVG-ON "low" and disable HVG operation.
Consequently, -200V will not be available and set shut down
with error 61.
Horizontal Collector Protection
If the horizontal pulse is not available due to some fault
condition, HOP will not detect Hfb from 1910 pin 11. This will
cause set shut down with error 61 to protect horizontal circuit.
9.4
CRT Board
Note: Description below refers to diagram D.
The RGB amplifier on the CRT board is just a traditional signal
amplifier with a high gain. It has two supplies, i.e., small signal
supply (+12V) and large signal supply (+200V). It amplifies the
RGB signal from the HOP IC with a level of <6V to the Cathode
output with level of >150V.
The overall voltage gain is defined by:
Vcathode= [4.5m * Rf +2Vbe] + 1.87 * R3212 / R3224 * (Vpin4-
Vpin2)
9.
EN 143
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