Display bars
Posted: Mon Jan 03, 2022 6:02 pm
All my Dragons, before a couple were modified to accept an external RGBTOHDMI, suffered from vertical jail bars and something resembling horizontal hum bars on the display.
My original display setup was:
Original Dragon PSU->Dragon->SCART to HDMI converter->LCD display.
The vertical jail bars were no worse than those seen on other retro computers of the era (Spectrum, C64 etc). When upgrading the RAM to 64K I took the opportunity to replace the 100nF RAM decoupling with a full complement of 1uF MLC decouplers. I can just about convince myself that they made a slight improvement. The jail bars were by no means off-putting though.
More of a distraction were the horizontal bars. On the default green display they occupied approximately one third of the screen height, were a slightly lighter shade of green and moved slowly down the screen. The bar moved over both the main screen and border. As the bar moved over screen text it distorted the text such that it moved a few pixels to the right. The display setup had no earth connections so a ground loop wasn't possible. I did, however, notice that disconnecting the colour burst from the video output stage (in preparation for RGBTOHDMI which does not, of course, produce bars) gave no horizontal bars on the resulting monochrome display. So the bars appear to be associated with the stock chroma circuit.
All the above is a long prelude to asking whether there are any existing recommended mods to help reduce or banish the above artefacts?
Alan
My original display setup was:
Original Dragon PSU->Dragon->SCART to HDMI converter->LCD display.
The vertical jail bars were no worse than those seen on other retro computers of the era (Spectrum, C64 etc). When upgrading the RAM to 64K I took the opportunity to replace the 100nF RAM decoupling with a full complement of 1uF MLC decouplers. I can just about convince myself that they made a slight improvement. The jail bars were by no means off-putting though.
More of a distraction were the horizontal bars. On the default green display they occupied approximately one third of the screen height, were a slightly lighter shade of green and moved slowly down the screen. The bar moved over both the main screen and border. As the bar moved over screen text it distorted the text such that it moved a few pixels to the right. The display setup had no earth connections so a ground loop wasn't possible. I did, however, notice that disconnecting the colour burst from the video output stage (in preparation for RGBTOHDMI which does not, of course, produce bars) gave no horizontal bars on the resulting monochrome display. So the bars appear to be associated with the stock chroma circuit.
All the above is a long prelude to asking whether there are any existing recommended mods to help reduce or banish the above artefacts?
Alan