(fwd) Model 4 video problems

Can any expert out there help me with this? Thanks! In comp.sys.tandy, bluesky6(a)ix.netcom.com (Benedict Chong) wrote: %I just got a Model 4. When I turn it on, the disk drive will spin but %there's no video. % %When the video brightness is increased, I can see a large rectangular %green area where the video would be. % %Instead of video characters, there are lots of zigzag lines across the %screen, with more on the top of the screen than towards the bottom. %The entire screen is stable and does not flicker or move around. % %It has been a good number of years since I last played with this kind %of video (built a 6502/6845 terminal in the mid 80s) so I can't %remember what problem would cause this type of symptoms. % %When I remove the video connector (after opening up the machine), the %screen loses the vertical hold. I guess that would mean that the %vertical sync and circuitry is working. % %Could the problem be due to the monitor circuitry or a problem with %the Horizontal Sync generation? % %Would appreciate all/any pointers. % %Ben %