He's still functional, but barely.
5 seconds sound clip from The Transformers (1984) - Heavy Metal War TV Series.
You can hear this line at 00:14:01 in the DVD version of the movie.
Quote context
[...]
- You were good, Optimus Prime. But not good enough to fight Megatron!
- It is over! Optimus Prime has been defeated!
- All Autobots must exile themselves to deeper space!
- No. I can't believe it. Optimus Prime, beaten by Megatron.
- He's still functional, but barely.
- My fault. Underestimated Megatron. Never suspected he had so many powers. I was not prepared.
- Well, I'm prepared, to knock those Deceptibums all the way back to Cybertron.
- No. Megatron has beaten me, according to Cybertron law.
- To violate that law would destroy our honor. We will comply and leave this Earth forever.
[...]