There are several errors in the schematics and you just found another one. I traced the PCB artwork in the Service Manual and the signal that is labeled GND is actually an audio return "ground" for the AFO audio output. It goes to the speaker jack on the right edge of the Display unit.
So it appears that the only DC ground is indeed the YGND, which isn't a very good design. But I'm sure there's a reason they had to make a compromise.
As to your display symptom, I haven't had to work on a unit that had that problem. If you have an external monitor that will take an NTSC signal, then plug it into the rear video output jack. If you get a picture, then the video signal from the main unit is good and the problem is probably in the display head. If you don't get a picture on the external monitor, then there is a problem with video encoder or LCD control circuits on the Logic board.
, wrote :
I am working on a "hangar queen" IC-7000 with multiple problems. I am wondering if others who have been deep inside the 7K have noted this issue:
While the Service Manual a connection of both YGND and GND to the board foil on the Display Board, there is no such connection in my unit. The ground return for the entire front panel is via the shield on the video cable. There is no ground continuity between the Main Unit and the Display Unit unless the video cable is connected. One result of this is the unit cannot be turned on without the video cable plugged into the Main Unit.
This is perhaps a fault in my unit but I have painstakingly traced the lands on both sides of the Display Unit and I find no connection between the two grounds as indicated on the schematic.
Is this a known issue/feature or is this perhaps a symptom of my problem(s).
Problems at the moment are a display that remains in black, intermittently displaying unlocked video.
Warren Allgyer - WA8TOD