Service Manuals, User Guides, Schematic Diagrams or docs for : RCA TV TX81 FAULT & DATABASE

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TX81 FAULT  &  DATABASE


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                       Analyzing the RCA TX81/82 Horizontal Output Stage
The horizontal output stage found in the
RCA or GE TX81 or TX82 chassis differs
from conventional TV horizontal output
stages. While the TVA92 TV Video
Analyzer's Horizontal Out put Load and
Dynamic Tests can analyze the TX81/82
horizontal output stage, minor changes in
the lead connections and test
interpretations are required. This Tech Tip
briefly describes the operation of the
TX81/82 horizontal output stage and
explains how to use and interpret the
TVA92's Horizontal Output Load and
Dynamic Tests.

The TX81/82 Horizontal Output Stage
The horizontal output stage of most
televisions includes six basic components
(as shown in Fig. 1a): primary of the
flyback, damper diode, retrace capacitor,
output transistor, yoke, and yoke series
capacitor. A conventional output stage
applies a regulated B+ voltage from the               Fig. 1b: The non-conventional horizontal output stage found in the RCA or GE
power supply to the flyback primary. The              TX81/82 television chassis.
other side of the primary winding connects                                                     During normal operation, the horizontal
to the collector of the horizontal output                                                      output transistor is switched on by base
transistor.                                                                                    drive producing an increasing primary
                                                                                               current and magnetic field. When the
                                                                                               transistor is turned off, the flyback's
                                                                                               magnetic field collapses, charging the
                                                                                               retrace capacitor. When fully collapsed,
                                                                                               the retrace capacitor discharges,
                                                                                               producing current in the flyback primary
                                                                                               resulting in a magnetic field. With the
                                                                                               retrace capacitor discharged, the flyback's
                                                                                               magnetic field collapses and biases on
                                                                                               the damper diode to complete the hori-
                                                                                               zontal cycle. For a detailed explanation of
                                                                                               the operation of a conventional horizontal
                                                                                               output stage, See Sencore Tech Tip
                                                                                               #207, "Understanding The TV Horizontal
                                                                                               Output Stage."
 Fig. 1a: Conventional horizontal output stage found in most television chassis.
The horizontal output stage found in the              in the primary of LP03, voltage is                    current (increase deflection width) and
TX81 and TX82 chassis contains the same               developed in the secondary which biases               flyback secondary voltages, including the
components found in a conventional TV                 on DP11 applying a positive voltage to the            CRT high voltage. A decrease in induced
output stage. See the simplified schematic            flyback primary at pin 6.                             B+ voltage reduces deflection and high
of the TX81 and TX82 horizontal output                                                                      voltage. By varying the conduction time of
stage shown in Fig. 1b. The primary of the            The secondary voltage produced by LP03                the horizontal output transistor, the
flyback transformer (LP04) is located                 is determined by how much current flows               deflection and high voltage can be
between pins 2 and 6. The flyback damper              in the primary. The raw DC voltage from               regulated.
is DP13, retrace capacitor is CP18,                   the power supply is applied to pin 12 of
horizontal output transistor is TP10, and             LP03. The path for LP03 primary current is            Understanding The TX81/82
the yoke series capacitor is CP40.                    through blocking diode DP14 and through               Horizontal Output Stage
                                                      the horizontal output transistor. When the
In addition to these basic components, the            horizontal output transistor is driven on by          Let's take a look at the transformer action
TX81 and TX82 horizontal output stage                 base drive, current flows and produces an             and currents during one horizontal cycle of
contains a B+ transformer (LP03) and its              inductively rising current in the primary of          the TX81/82 horizontal output stage. Figure
damping components (CP14, DP17). It                   LP03.                                                 2a-d shows the action occurring at four
further includes blocking diodes and                                                                        distinct times during one horizontal cycle
capacitors (DP14, CP60, DP10, CP53). The              The design of the TX81 and TX82 chassis               starting with the horizontal output
B+ transformer (LP03) produces B+ to                  is such that the base drive to the horizontal         transistor turning on.
energize the flyback transformer. Its                 output transistor is varied in duty cycle or
damping components produce alternating                conduction time for each horizontal cycle.            When the H.O.T. turns on, current flows
currents in the primary, and damp                     A shortened conduction time permits a                 through DP14 and the primary of LP03
inductive voltages and energy returning               lower level of current build-up in the                (Fig. 2a). Voltage induced into the
into the primary. The blocking components             primary of LP03 reducing the secondary                secondary of LP03 produces a positive
isolate alternating currents in the primary           B+ voltage applied to the flyback. A                  potential biasing on DP11 and applies the
of LP03 and the flyback primary.                      lengthened conduction time permits more               positive potential to pin 6 of the flyback.
                                                      current buildup in the primary of LP03                The positive potential biases on DP10
The TX81 and TX82 chassis differs from                increasing the secondary B+ voltage                   producing a path for flyback primary
the conventional output stage in the                  applied to the flyback primary.                       current. Current flows through the H.O.T. -
manner that B+ voltage is produced and                                                                      DP10 through the flyback primary and
input to the flyback transformer. The B+              The level of secondary induced B+ voltage             DP11. The buildup of current in the
voltage to the primary of the flyback at pin          controls the flyback's primary current. By            primary is determined by how long the
6 is produced inductively by the secondary            increasing the B+ voltage, the flyback pulse          horizontal output transistor conducts.
of transformer LP03. When current flows               increases, resulting in an increase in yoke



                  HOT "ON"                                                                               HOT "OFF"
              (2nd part of trace)                                                                   (1st part of retrace)
                  Raw B+                                                                                   Raw B+
                            LP03
                                                                                                                     LP03
                                    +                                                                                       +

                                                                                                 CP14
                                               DP11                                            (Charges)
                                    



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