My 1993 Chevrolet Silverado truck radio locked up about a week after I had a hands free phone system installed. Do I need a code to unlock it or is it broken? What is the code or how do I know if its broken? I replaced the radio with a used one from a wrecking yard and it lights up exactly the same as the one I took out? Thanks for your help.

I assume it displays "LOC".....

There is a procedure for unlocking the radio..there is a back up code that can be obtained from the radio...then a new unlock code put in.
Stop at any GM dealer,they can do this for you..they'll get the backup code,call in ,get a new code and install/unlock the radio for you.

Radio does not display"Loc", it looks as it would should it be working but it won't work. Could it be the brain is broken?
Thanks