I just got a Close Encounters with no keys. I was hoping the backbox key would be hanging inside the cabinet when I drilled out the front door lock but no such luck. Had to drill out the backbox lock after an hour of trying keys, screwdrivers etc without any luck. Drilled out the lock but it still doesn't want to open...any tips or tricks to this?

I drilled and removed the whole lock core but I still can't open the backbox door

No, this is my only machine. Could it be reached from under the playfield?

When I looked up removing locks from backbox the majority of people said 'drill it out'. It'll be blind luck if I can get this open after looking at those latches.

There's an aluminium plate under the vent holes that stops any access.

Yes I'll try this but it might be a bit tricky through the drilled out lock. I'll let you know if I have any luck...thanks.

So the locks been drilled out in your photo hasn't it? I think the top latch has unlocked but the lower one's still holding on. Might try putting it on it's side like you suggested.

Dunno 'bout 3m long arms. I pulled the playfield back and using a flat bladed screwdriver, I was able to reach up under the playfield and unhook the lower latch and the door opened...you beauty!
Thanks for all the responses...much appreciated! I'm glad I didn't have to butcher anything