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Old 11th Jan 2017, 3:28 pm   #3
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
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Default Re: Running 15.75kHz VDU's at 21.85Khz

Quote:
Originally Posted by dragonser View Post
I did manage to damage a cub microvitec monitor trying to get it to work at a higher line frequency.
This is why in the modification to the IBM 5153 monitor the zener array is added to prevent failure of the horizontal output transistor. It is an interesting balance of factors. If the tuning capacitance on the line output transformer is dropped in value to allow the shorter flyback time for EGA, the peak voltage on the H output transistor collector increases.This is offset to some extent with reduced width which occurs when the H rate is increased anyway, but it still needs the additional zener array as outlined in the article. Also as noted there, IBM got away with it well in the 5154 monitor, because they separated the EHT generation from the H scanning system.
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