HMV 2701: Picture defocused , fades and disappears

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Question

Before the raster disappeared the picture would fade and become defocused every couple of seconds. On examination, the fusible resistor R1 on the power supply board was found to be open-circuit. This is in series with the h.t. supply to the e.h.t generator transistor VT7. On turning the hold control the line oscillator could be heard to be working. VT7 was replaced therefore, along with VT6 which controls its h.t. supply, but still no raster. These two transistors and their heatsinks are hot and there is no 8kV pulse from the e.h.t. transformer.

Solution

Disconnect the tripler input lead ( plug/socket 12) from the e.h.t. transformer. If this restores the 8kV pulse the tripler is faulty. If not, suspect the e.h.t. transfoemer of having shorted turns

Thorn 2000 Chassis

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