QL Video issue - Red color missing

Nagging hardware related question? Post here!
User avatar
QL Wafer Drive
Posts: 1604
Joined: Sun Feb 13, 2011 10:53 pm
Location: SW Germany

Re: QL Video issue - Red color missing

Postby tofro » Thu May 17, 2018 12:21 pm

Your picture quality is incredibly good considering you are using the modulator.


ʎɐqǝ ɯoɹɟ ǝq oʇ ƃuᴉoƃ ʇou sᴉ pɹɐoqʎǝʞ ʇxǝu ʎɯ 'ɹɐǝp ɥO
User avatar
Super Gold Card
Posts: 539
Joined: Sun Dec 11, 2011 1:16 am
Location: Looking forward to summer in Somerset, UK...

Re: QL Video issue - Red color missing

Postby 1024MAK » Sat May 19, 2018 1:11 pm

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.


QL, Falcon, Atari 520STFM, Atari 1040STE, more PC's than I care to count and an assortment of 8 bit micros (Sinclair and Acorn)(nearly forgot the Psion's)
ROM Dongle
Posts: 8
Joined: Sun May 06, 2018 10:14 am
Location: Barcelona, Spain

Re: QL Video issue - Red color missing

Postby Quickie » Mon May 21, 2018 6:23 pm

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!

Who is online

Users browsing this forum: No registered users and 5 guests