- Joined
- Aug 30, 2001
- Posts
- 349
After encountering a Neo Geo AES revision 1 board (running via SCART RGB cable to a tiny PVM) that had wavy video at the top part of the screen,
I found others had the same problem but had no resolution.
http://www.neo-geo.com/forums/showthread.php?20236-wavy-monitor
http://www.neo-geo.com/forums/showthread.php?215136-Wavy-top-of-the-screen-on-RGB-tv-monitor
http://www.neo-geo.com/forums/showthread.php?254927-Big-Red-monitor-wavy-at-top-Pic-included
http://www.neo-geo.com/forums/showthread.php?206523-Monitor-or-Motherboard-issue-Top-of-screen-wavy
http://www.neo-geo.com/forums/showthread.php?264099-Neo-Geo-AES-Does-my-capacitor-s-need-replacing
I checked for:
1. interference from the 2 daughterboards on the system (1 for converting it from 5V to 10V, 1 for some video oscillator),
2. loose traces, particularly at the Sony CXA 1145 video encoder,
3. and played around with both variable capacitors on the board,
however, there was no change.
Picture of the board:
I noticed the severity increased with activity on the screen and it occurred to me that the sync was contaminated with noise and that it was likely from video or sound information.
I then checked the RGB cable and discovered that the DIN side pin 3 was wired to the Sync input for the PVM/Monitor. Pin 3 outputs Composite Video (it also includes Composite Sync information). To get a clean sync signal, it would have to be stripped with an LM1881, however, as this was an early revision board, pin 7 was already outputting a clean Composite Sync signal.
A resolder of the Sync wire from pin 3 to pin 7 completely resolved the issue.
Putting out there for future reference.
NB: the vertical lines appear pronounced due to the screen being a tiny 6-inch PVM, and not because of the issue plaguing Rev 3-6 boards.
I found others had the same problem but had no resolution.
http://www.neo-geo.com/forums/showthread.php?20236-wavy-monitor
http://www.neo-geo.com/forums/showthread.php?215136-Wavy-top-of-the-screen-on-RGB-tv-monitor
http://www.neo-geo.com/forums/showthread.php?254927-Big-Red-monitor-wavy-at-top-Pic-included
http://www.neo-geo.com/forums/showthread.php?206523-Monitor-or-Motherboard-issue-Top-of-screen-wavy
http://www.neo-geo.com/forums/showthread.php?264099-Neo-Geo-AES-Does-my-capacitor-s-need-replacing
I checked for:
1. interference from the 2 daughterboards on the system (1 for converting it from 5V to 10V, 1 for some video oscillator),
2. loose traces, particularly at the Sony CXA 1145 video encoder,
3. and played around with both variable capacitors on the board,
however, there was no change.
Picture of the board:
I noticed the severity increased with activity on the screen and it occurred to me that the sync was contaminated with noise and that it was likely from video or sound information.
I then checked the RGB cable and discovered that the DIN side pin 3 was wired to the Sync input for the PVM/Monitor. Pin 3 outputs Composite Video (it also includes Composite Sync information). To get a clean sync signal, it would have to be stripped with an LM1881, however, as this was an early revision board, pin 7 was already outputting a clean Composite Sync signal.
A resolder of the Sync wire from pin 3 to pin 7 completely resolved the issue.
Putting out there for future reference.
NB: the vertical lines appear pronounced due to the screen being a tiny 6-inch PVM, and not because of the issue plaguing Rev 3-6 boards.
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