Dragon32 Video Output Issues

For the discussion of all hardware related topics.
Post Reply
goobler
Posts: 5
Joined: Thu Dec 07, 2017 5:32 pm

Dragon32 Video Output Issues

Post by goobler »

I have a Dragon32 that is working great apart from a poor video signal.

It has some sort of signal interference which causes a bit of flashing and color loss. This happens on both RF and composite output.

Does this sound familiar to anybody, anyone have any hints on where to start troubleshooting?
sorchard
Posts: 530
Joined: Sat Jun 07, 2014 9:43 pm
Location: Norwich UK

Re: Dragon32 Video Output Issues

Post by sorchard »

It might be worth tweaking the video trimmers on the main board to see if that helps. The variable resistors can sometimes go bad over time and can be restored somewhat with a bit of movement.

There is a 10K pot just below the power connector that adjusts the DC bias. You should see the brightness change over the range of adjustment, with loss of colour if too far out.

Some boards also have a trimmer cap just below the crystal to the left of the power connector. This fine tunes the colour subcarrier frequency, and you can lose the colour if this is too far out. It also affects the appearance of the dot crawl effect.

Older boards have another 10K pot a bit further down on the left. This adjusts the phase of the colour burst. If too far out you get the wrong colours or again no colour at all.

Take some photos of the positions before you move anything so you can get back to how it was.

All that being said some TVs and decoders just don't get on well with the video signal coming out of the Dragon, as it is not true interlaced PAL. It might be worth trying on a couple of different displays if you can.
Stew
Post Reply