Audio system kaput?

Hi all! I think my audio unit (CD player / radio / whatever you want to call it) is busted. I drive a Gen II base Prius (meaning no JBL, so the audio unit is model #86120-47090).

Things that DON'T work:
- no radio audio, no CD audio
- seek function doesn't find any stations
- scan function does nothing
- backlight turns off when unit is powered on (this is not normal behavior, right?)
- when the volume is cranked, a hiss can be heard, as well as a low-frequency pulse repeating at about 0.5Hz to 1Hz intervals

Things that DO work:
- beeps from MFD
- audio unit functions displayed on MFD (including volume, current station, "NO CD", etc)
- all fuses labelled "audio system" in the manual have been checked and are working.
- looking at the PCB, it does not seem that any components are fried

(Side note: am I correct in understanding that in the base unit, the amp is built directly in? Meaning, is there a direct shot from the wiring harness to the speakers? Try as I might, I haven't been able to find a wiring diagram. I may just be bad at searching. [And apologies if I've missed some crucial post on this site and have reposted - but I've been scrounging for the better part of 2 weeks and haven't been able to find a similar case.])

Thoughts? I'm just looking for confirmation of busted-ness so I can replace it.