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Old 7th Oct 2015, 12:15 pm   #36
FERNSEH
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Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
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Default Re: Ferguson 247T: huge console TV set.

The circuit of the gated and amplified vision AGC system. The negative going line sync pulse present at the anode of the sync separator is differentiated by a low value capacitor and the positive going trailing edge which is co-incident with the back porch of the line sync allows the V7 to conduct only in that period. The resultant vision signal amplitude dependant pulse is rectified by the EB91 V8A. Delayed AGC is supplied to the tuner from diode W103.

The vision AGC system is now working correctly but there are still problems with the line flywheel discriminator to sort out.
Refer to the circuit on post 32. The cathodes of the EB91 are not receiving any sine wave drive from the discriminator transformer. The coils rsistances are correct, 66 + 66 ohms. It's possible the 0.01mfd capacitor C172 is OC.

DFWB.
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Last edited by FERNSEH; 7th Oct 2015 at 12:28 pm.
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