I know somebody with a PS3 and I want to log into my old PSN account but I'm scared it'll log him out and he doesn't know his PSN password.
I don't have an answer to your question, but a different solution.
If he doesn't remember his password he can still recover it with his email address:
Forgot your password?from the sign-in ID (e-mail address) and password screen.
- Enter your sign-in ID (e-mail address) and birth date.
- Reset your password using a PC.
An e-mail message is delivered to the address that you used as your sign-in ID. Follow the steps in the e-mail message to reset your password using a PC.