ITT CVC9

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The tube is blanked out at the centre, and to avoid damage
the tripler must be disconnected. The RGB output
transistors are all switched hard on – only 15V at their
collectors. There’s 15V at the RGB output pins of the
TDA1327A colour demodulator/matrixing i.c. instead of
6V. Removing the i.c. results in the voltages at the
collectors of the RGB output transistors rising, but fitting a
replacement does not cure the fault.
The d.c. levels at the RGB output pins of the TDA1327A
i.c. are under the control of the voltage at pin 3 (luminance
input). You’ll probably find this wildly incorrect. If so,
check the beam limiter transistor T24, the voltage at the
cathode (pin 9, sensed to give the beam limiting action) of
the PL509 line output valve, and the presence of 15.8V at
the top of the preset brightness control R90. If these points
are in order, check the black -level clamp diodes D21 and
D22.

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