Page 4 of 4
Re: Switching graphic pages
Posted: Sat Oct 11, 2014 11:25 pm
by Alastair
sorchard wrote:There is a trimmer capacitor on the main board near the power connector that can be adjusted to reduce the appearance of the patterns but the setting has a tendency to drift with time. It's very sensitive and is best adjusted with a plastic trim tool. A metal screwdriver has enough capacitance to interfere with the adjustment.
Please tell me more, are you talking about RV2 as seen on
this motherboard picture?
Re: Switching graphic pages
Posted: Sun Oct 12, 2014 9:21 am
by sorchard
pser1 wrote:If the synchro problem between the two clocks is 'hardware' related ... maybe it could be changed?
I won't mind to add a daugther board if necessary!
To get two clocks to run in sync would need someone with far more skill than me to figure out. Though if a daughterboard is OK, then an easier solution would be to make an RGB conversion board. The output from the 6847 is actually pretty good quality, so it would make sense to convert these signals direct to RGB with a few video opamps. (Plus a couple of extra components to make a composite sync) I've got a feeling other people have already worked on this so there may already be a solution.
Alastair wrote:Please tell me more, are you talking about RV2...
The trimmer cap to tweak the colour carrier frequency is C32 on D64 boards and C7 on D32 MKII boards.
On older boards C7 is just an ordinary capacitor, though it could be replaced by a 2-22pF trimmer.
RV2 on the photo you referred to looks like the video DC level adjust. I think RV1 on this board adjusts the colour burst phase, so may have a useful effect on the interference patterns, I don't know for sure to be honest.
Just to add to the confusion, many Dragon boards appear to not have RV2 and RV1 is the DC level adjust.
Re: Switching graphic pages
Posted: Sun Oct 12, 2014 10:53 pm
by Alastair
sorchard wrote:The trimmer cap to tweak the colour carrier frequency is C32 on D64 boards and C7 on D32 MKII boards.
On older boards C7 is just an ordinary capacitor, though it could be replaced by a 2-22pF trimmer.
Thanks, goodness knows why I confused a variable resistor with a trimmer cap! Unfortunately on my D32's board C7 is an ordinary capacitor and I am extremely reluctant to carry out any unnecessary soldering work on it, so I'm going to leave it alone.
