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Old 29th Aug 2019, 3:42 pm   #180
FERNSEH
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Join Date: Mar 2005
Location: Gateshead, Tyne and Wear, UK.
Posts: 6,339
Default Re: Baird T5 restoration project.

The sketch shows the DC restorer in the T23. There is something not right about this circuit. The positive going video is supplied to the CRT grid. The function of the DC restorer diode is to conduct on the sync pulse tips to the DC reference level set by the brightness control. Normally the DC reference will be a positive voltage but in the Baird T23 it is negative and in all accounts this is the wrong polarity for the circuit to work properly.

If it is at all possible the brightness control circuit will be rearranged so that the CRT cathode voltage will be controlled in the same manner as the in the model T20. The video drive to the CRT grid will be DC restored with the reference level at a fixed potential.
See the third attachment in Andy's post No. 176.

The second attachment in this post shows the overly bright picture on the screen of the Cossor CRT.

DFWB.
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Last edited by FERNSEH; 29th Aug 2019 at 3:47 pm.
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