Hi everyone,
This is my first post here!
I'm modifying an old console and part of that modification is putting a physical DPDT switch between a 53.2xxxMhz oscillator for PAL and a 53.6xxxMhz one for NTSC. One terminal on the switch physically moves the timing trace from one crystal to the other, and the other terminals send a ground signal to a pin that tells the console it's now running in NTSC mode.
These oscillators, through various multiplications/divisions, control the timing of the entire system. The difference is less than 1% between the two, and the system will run fine in NTSC on the PAL crystal, but the difference in timing causes some on screen artifacts, mostly that jail bars appear on black. These are not ideal so I wanted to allow for a dual oscillator option.
The switch works fine, however in order to use the switch there's extra trace added that's increased line capacitance, about 10CM or so of single cored 22 AWG wire. The problem is, this now causes a rippling effect on screen due to the extra capacitance interfering with the timing signal.
Does anyone have any suggestions for overcoming this issue?
Many thanks,
Dan.
This is my first post here!
I'm modifying an old console and part of that modification is putting a physical DPDT switch between a 53.2xxxMhz oscillator for PAL and a 53.6xxxMhz one for NTSC. One terminal on the switch physically moves the timing trace from one crystal to the other, and the other terminals send a ground signal to a pin that tells the console it's now running in NTSC mode.
These oscillators, through various multiplications/divisions, control the timing of the entire system. The difference is less than 1% between the two, and the system will run fine in NTSC on the PAL crystal, but the difference in timing causes some on screen artifacts, mostly that jail bars appear on black. These are not ideal so I wanted to allow for a dual oscillator option.
The switch works fine, however in order to use the switch there's extra trace added that's increased line capacitance, about 10CM or so of single cored 22 AWG wire. The problem is, this now causes a rippling effect on screen due to the extra capacitance interfering with the timing signal.
Does anyone have any suggestions for overcoming this issue?
Many thanks,
Dan.