no sound from my stock delco radio

I have a 1999 Monte Carlo. The radio functions as it should (changes channels/time/playing cd) but I have no sound. I went to the salvage yard and put in 2 identical radios and they acted the same as my original radio. These radios did not display the LOC anti theft .

Where should I start looking?

Thanks in advance for your suggestions!

sounds like all the speakers are blown. Try and connect up another speaker to one of the speakers in the rear to see.

1) Have the radio bench tested, because the Amp finals could be blown.
If the radio is turned on without a load (speakers), it could damage the final amps.