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Old 1st Mar 2018, 10:48 am   #27
FERNSEH
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Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Default Re: Marconiphone VT161 17" TV

Hi Nick,
have you scoped the waveform present on the anode of the triode section of the PCL82? Notice that the bottom end of the ramp forming capacitor C91 is returned to the cathode of the pentode section. A parabolic waveform is developed across the cathode bypass capacitor C92 100uF and this is added to the sawtooth waveform developed across C91. The coupling capacitor C93 has an unusually low value, 0.02uF.
That strange pulse at the beginning of the forward scanning stroke could introduce ringing in the scanning coils. The frame blanking period is 1.4milliseconds so in fact that pulse will introduce the disturbance outside of the picture part of the frame scan.

DFWB.

Last edited by FERNSEH; 1st Mar 2018 at 10:55 am.
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