S900 + A2 + Z15-GH4 + Lumix GH3+ Lightbridge + Futaba T14SG
Is it possible to receive HD video signal in this configuration? I try to connect lightbridge air system like it shows manual - scenario 4. It seems there is no communication through the Gimbal Cable and G7 port. CONTROL Indicator is GREEN but VIDEO Indicator is solid RED. I'm sure I've mapped all 12 channels correct [CH 9-12 to the gimbal Tilt, Pan, Mode and Shut] but I can not control gimbal and I neither can not see video. Lightbridge works fine with NAZA V2 and Zenmuse H3-3D in HD.

Try to connect GH4 directly do LightBridge (as you do with gopro). Is it working?
If yes - you can have broken Z15 hdmi/av board or/and hdmi cable. Connact DJI support.
If no - troubleshoot further via led signals.

What about the LED on GH4 gimbal ?