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Re: QL Video issue - Red color missing

Posted: Thu May 17, 2018 12:21 pm
by tofro
Your picture quality is incredibly good considering you are using the modulator.


Re: QL Video issue - Red color missing

Posted: Sat May 19, 2018 1:11 pm
by 1024MAK
Protecting the 8301 ULA
Rather than just using 5.6V Zener diodes, adding some fast signal diodes can improve the protection. Use 1N4148 or similar. Connect a diode between 0V/GND and the signal pin, then another diode between the signal pin and the +5V power rail. Do this for all the signals that go to the RGB socket.

Code: Select all

       A  K             A  K
0V ----->|-------+------->|------- +5V

You can of course retain the 5.6V Zener diodes.

The signal diodes will clamp any out of range voltage spikes within their current ratings.


Re: QL Video issue - Red color missing

Posted: Mon May 21, 2018 6:23 pm
by Quickie
Hi all,

Thanks again for all the provided information and suggested mods and improvements. This really increases my interest on the QL! :)
Unfortunately I am currently trying to fix a couple of Dragon32's and I would prefer repairing them before retaking on the QL (which I currently consider fixed, but misses the improvement) :)

Best regards!