Hi Philippe,
I'm sorry, I was very busy with other Videopac projects.
I do have a service manual of the C52, but I don't have a scan of it. Please refer to the scan of the G7000, as it is almost the same.
pt 5 should be connected to pin 11 of IC 669 with an extra inverter (74LS04)
pt 6 should be connected to pin 6 of IC 668 with an extra inverter
pt 7 should be connected to pin 3 of IC 668

