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electrode of V513, the pulse width of which is controlled by capacitance C514. The collector
electrode and emitter of V512 are merged between the base electrode and the emitter of
switch tube V513. The conducting state of V512, i.e., the current through V512 controls the
conducting time of V513. If the current through V512 is high, the conducting time of V513 is
short and the voltage low. If the current through V512 decreases, i.e., the shunting effect
decreases, the conducting time of V513 is long and the voltage high. The working status of
V512 is controlled by the control circuit composed of V551, VD551 and VD515. Direct
sampling is adopted for the control circuit and the photocoupler transmits error information.
V551 is error comparison amplifier. VD515 transmits error information. The error
information changes the current through V511 and the change generates error voltage on
resistance R515 to control the conducting state of V512, thus the conducting time of V513 is
changed and the purpose of width is achieved. When the output DC voltage B1-115V
increases, the current through V551 increases by the photocoupler, so the current through
V512 increases, making the conducting time of V513 shorter, output voltage lower, thus
achieving the purpose of regulation, and vice versa. With VD554 rectification, C559 filtering
and V552 control, the pulse voltage supplied by the secondary pole of the switch transformer
becomes 26V, which is supplied to vertical scanning circuit. With VD553 rectification, C557
filtering, 15V voltage is obtained, which is then regulated through three-stage adjustment to
become the 12V, 9V and 5V voltage supplying to the main chassis circuit.
DISASSEMBLY INSTRUCTIONS
A. Important note
This set is disconnected from the power supply through the converter transformer. An
isolating transformer is necessary to service operations on the primary side of the converter
transformer.
Back Cabinet Removal
Remove the screw residing on the back cabinet and carefully separate the back cabinet from
the front cabinet.
B. Picture tube handling caution
Due to high vacuum and large surface area of picture tube, great care must be exercised when
handling picture tube. Always lift picture tube by grasping it firmly around faceplate.
NEVER LIFT TUVBE BY ITS NECK! The picture tube must not be scratched or subjected to
excessive pressure as fracture of glass may result in an implosion of considerable violence
which can cause personal injury or property damage.