tormod wrote:It would be a follow-up of this: viewtopic.php?f=5&t=4455&p=9673 (that's one year now and I haven't gotten back to it ). I am envisaging a connector board with matching connectors for both the switching PSU and the Dragon motherboard, and which also includes the new S-video circuitry. I am just a bit worried what kind of RF noise a 2.50€ supply can produce and how it may affect the video signal.
Interesting thread. I only joined the forum this year and it looks like I've missed out on a lot of stuff. I'm pleasantly surprised by the improvement obtained with the S-Video conversion.
@tormod: If you're going to the trouble of making a PCB, then you may as well include some L-C filters which will help reduce the switching noise passed on to the rest of the system, though the biggest noise producer is the Dragon itself. It really is terrible (like many home computers of the day) and would probably fail modern EMC requirements miserably. When I was a kid I used to tune my AM radio so I could hear the Dragon processing!
That reminds me: On some Dragons I've seen a series of fixed vertical dark lines on the text display with a spacing similar to the width of a character. This is an example of noise synchronised with a display. It can be cured by fitting the missing 100n bypass capacitors to the memory array. Presumably they were left out to reduce cost. I imagine this can also happen if one of the larger caps on the 5V line fails.