Here is a link to the service manual for your Tyros 3. In the paragraph below the image on the download website you have to wait until it changes from saying processing to Get Manual before you can download it.
As best as I can determine it appears that all the C# and G# notes are fed by a +50V supply fed via resistor R36 (33KOhms) on what I think is the EMKS FD board. It is designated lead MK20 and leaves the board on Connector CN5 pin 11 which then is wired to Connector CN3 on MKH-D board pin 11 where it wired to some of the C# and G# keys. It then also leaves that board on CN4 pin 22 and goes to CN1 on MK61L board pin 22 to pick up the rest of the C# and G# keys.
As you state that every one of the C# and G# is not working I suggest that you check that R36 is OK and that you have correct voltage leaving the EMKS-FD board CN5 pin11. If you test the voltage levels on pins 1-12 on CN5 they should all be the same voltage (I think) as all these leads are connected to +50V via a 33KOhm resistor to feed all the notes (keys)
I know you said that all the relevant keys are not working but if only some of the keys are working suggest you work thru each connector until you find the one where the voltage is missing.
It may also be if only a set of keys are not working that the wiring between the keys on a particular board may be faulty.
Hopefully this is of some help