I shall be a passenger in transit at Beijing T3. Do I go thru any security checks or straight to dep

I am afriad that you still need to go through the security check.
The procedures is similar like this: Arrive at the International Arrival Level at 3F of T3-E → proceed with transfer procedures → pass through the Transit Inspection in special passage in the east or west → take special elevator downstairs to International Departure Level at 2F of T3-E → accept Security Inspection in the special passage → go through the customs sample check of hand baggage if necessary → Waiting & Boarding
Hope it can help you.

Thank you very much, indeed. Yes, it is very helpful.