As mentioned elsewhere I got a P3Adv with a dead camera. The gimbal appears to function correctly.

Is there a procedure for checking the various bits of the camera and gimbal assembly to find where the problem is, other than swapping suspect components for good ones?

I have tried a working camera and gimbal on the drone and and they work, conversely the dead camera and its gimbal give no image or camera data/controls when connected to the 'donating drone' but the gimbal appears to function correctly.
I thought I had spotted a somewhat displaced ribbon cable connection but releasing the cable, cleaning its contacts with IPA and reconnecting the cable did not give an image.

I have had the back of the actual camera case off and it appears that the 'gubbins' are held in place by a number of screws and the actual camera might be removable from its case. I recollect seeing a thread which mentioned that some screws allow the positiion of the sensor wrt the case to be altered so I need to check which screws to NOT remove.

Thanks for any answers

Hello and good day Sean-newbie. I am sorry for the trouble and to know that you are having issue with the camera of your DJI Phantom 3 Advanced. Since this issue is happening on your DJI Phantom 3 Advanced. I would recommend you contact our support team for further help at https://www.dji.com/support?site=brandsite&from=nav . We have the professional team who would do their best to fix the issue and then the corresponding resolution would be provided. Please note that the repair cost will depend on the warranty period of the said drone; otherwise, valid charges will apply. Just a friendly reminder that  DJI do not recommend doing a DIY repair on the said drone. To avoid additional damage and this can void the warranty of the drone as well. Thank for understanding and for your support.

Thanks Stephen but this is at least a 2nd hand drone with which there is no warranty. So, at a guess, a repair would cost more than I paid for the entire drone.
Plus I would learn nothing from the experience and I am quite interested in being able to attempt to the repair myself or at least find the broken component.

Check this OP from another site.  Go through the flow chart to help diagnose and isolate your problem.  See what you come up with.  As the OP states, the trouble-shooting transfers to a P3A too most of the time.  Come back here with questions / problems etc.

https://phantompilots.com/thread ... -on-ph3-pro.133487/

Good luck

Ta Mark, going now.
Update.
I tried the flow chart but my situation doesn't follow it that well as I have no control over the camera and trying to take a photo via the controller fails or at least there is no image on the mSD card.

However I came across a video of the dismantling of the camera/gimbal and it didn't look too bad wrt the motherboard (MB) and camera sensor board so I swapped MB's and the suspect camera gives an image.

The suspect MB did not give an image with a good camera. The MB contacts on the ribbion cable had some white marks on them and this was cleaned off, to no effect.

I see one screw which might hold the MB into its housing but the MB doesn't seem to want to move when that screw is removed.
Does anyone know if the MB is 'stuck down' in its housing?
I see no obvious damage on the MB but given the TINY size of some of the components..............
Is it possible to clean the contacts inside the ribbon cable connectors with, say, a piece of paper being pushed into and pulled out of the ribbon cable connectors or would this be too aggresive?
Ta

I personally haven't replaced a ribbon cable yet.   

All I can tell you is if you decide to replace the ribbon cable, be sure to use an OEM cable.  Aftermarkets only work about half the time, so I hear.

Good luck

I would dread having to replace the ribbon cable, it was 'stressfull' enough peeling it off the cover for,  and foam pad on, the MB. Or maybe it's a case of my being too careful. The glue or double sided tape etc. used in the assembly process certainly does its job lol and it looks like the cable is stuck down in quite a few places.
Fortunately it looks like the cable is ok though I did spot what looks like one impact mark on it but the mark does not seem to have damaged the insulation.