Radio head unit can't detect CD changer

[AZ91525ia]

I have a stock radio head unit and it connects to Pioneer CDX-M30 CD changer. It worked wonderfully last 4-5 years. Suddenly, the head unit doesn't detect the CD changer any more, when I try to switch from AM/FM to CD by pushing the "BAND" button. The head unit only rotates from FM -> AM, not FM -> AM -> CD. The CD changer still receives and ejects the CD magazine properly, no "DISC ERROR" etc.

I borrowed the same CDX-M30 changer from a friend, the head unit is still unable to recognize the changer. Basic check to cables seems fine, no bent pins or loose connections. Bad head unit? Any ideas?

Thanks,
Jerry
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