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FERNSEH · 14th Aug 2019, 4:41 pm

The frame timebase was an easy fix. Oscilloscope connected to the control grid of the PCL82 frame OP valve. A Sawtooth waveform present but it is apparent that the timebase is running too slow. Check the value of R87 (3.3megohms) and it is >5megohms. After replacing the faulty resistor the frame hold control can be adjusted for 20mS repetition rate. Sawtooth waveform at the anode of the PCL82 is 50volts P - P + flyback pulse.

DFWB.

14th Aug 2019, 4:41 pm	#16
FERNSEH Dekatron Join Date: Mar 2005 Location: Gateshead, Tyne and Wear, UK. Posts: 7,444	Re: Stella ST1007U The frame timebase was an easy fix. Oscilloscope connected to the control grid of the PCL82 frame OP valve. A Sawtooth waveform present but it is apparent that the timebase is running too slow. Check the value of R87 (3.3megohms) and it is >5megohms. After replacing the faulty resistor the frame hold control can be adjusted for 20mS repetition rate. Sawtooth waveform at the anode of the PCL82 is 50volts P - P + flyback pulse. DFWB.