Re: Sega SC-3000 video daughterboard.
Posted: Wed Feb 20, 2013 9:30 pm
Hi Honest Bob, I've fixed it!!!!!!!!!
'It' being the original subject of this post - my NZ model SC-3000.
I desoldered the T101 circular transformer, did a few checks, wired up the 12v rail to my bench PSU - wow - instant video fix!
I tested how low the voltage could go - saw some very interesting results on my composite monitor (CM8833-II):
12.6V - Functional. Colours quite washed out
12.0V - Colours a bit better.
11.6V - Colours OK
11.1V - Colours more saturated, looks great
<11.1 - Colours more saturated, some diagonal banding showing
9.7V - Great saturation, banding gone!
9.0V - Acceptable colours, slight shimmer.
8.8V - Monochrome
<6.6 - Vertical hold gone, picture unviewable
Q. Why not just run the whole daughterboard off 9V? Or, convert to run off 12, chuck an extra regulator in, to feed the main 5v regulator (12 to 5 would be lots of heat in one place) and maybe a fat diode to drop the 12 to about 11.2 volts for the video daughterboard.
The shimmering/banding I can see changes frequency with voltage - so reckon could be eliminate with a fews caps in right places.
And here it is!
'It' being the original subject of this post - my NZ model SC-3000.
I desoldered the T101 circular transformer, did a few checks, wired up the 12v rail to my bench PSU - wow - instant video fix!
I tested how low the voltage could go - saw some very interesting results on my composite monitor (CM8833-II):
12.6V - Functional. Colours quite washed out
12.0V - Colours a bit better.
11.6V - Colours OK
11.1V - Colours more saturated, looks great
<11.1 - Colours more saturated, some diagonal banding showing
9.7V - Great saturation, banding gone!
9.0V - Acceptable colours, slight shimmer.
8.8V - Monochrome
<6.6 - Vertical hold gone, picture unviewable
Q. Why not just run the whole daughterboard off 9V? Or, convert to run off 12, chuck an extra regulator in, to feed the main 5v regulator (12 to 5 would be lots of heat in one place) and maybe a fat diode to drop the 12 to about 11.2 volts for the video daughterboard.
The shimmering/banding I can see changes frequency with voltage - so reckon could be eliminate with a fews caps in right places.
And here it is!