Sony CDP-C79ES strange behavior

Hello All ANers, I'm a newbie, seeking advice. My system consists of (all Sony): STR-DA4ES Receiver, TC-WA9ES cassette deck, BDP-S1000ES blu-ray player, BDP-S350 blu-ray player, CD-RW33 CD burner, PCM-R300 DAT deck, CDP-C79ES CD 5 disc changer, LDP-600 LD player, SLV-998HF VCR, KV-32XBR6, KV-32XBR9, KV-32HS510 televisions, WM-D6C portable cassette deck, TCD-D8 portable DAT deck, ECM-929LT microphone. Now, on to the non-Sony gear: Four TrippLite suppressors, (7) JBL S26II speakers, (2) Infinity SM120 tower speakers, Energy EPS-150 subwoofer, Yamaha YST-SW200 subwoofer. Cabling is a mix of everything from Esoteric Audio, Parts-Express house brand, Belkin (high MSRP but bought on factory buy-out deals). I'm sure all of above pales in comparison to what some of you true audiophiles have spent over the years. On to my quandry: The C79 ES is really malfunctioning badly. The deck was bought in 1993 and has had medium use. Approx. 3 months ago I pushed the power button in, (the deck had been sitting w/o any use for 2 months or so), and nothing happened.I toggled the switch numerous times, nothing. I left the switch depressed and went about my business, to come back 3 hours or so later and find the unit on.So I left the power button depressed for several days, wondering if Sony used something akin to the CMOS batteries that were used in the x86 families of PCs. It was not a fix, to be sure. Even if you leave it powered up constantly now, only a few features work like Skip Disc, but you can not play a disc.It is such a beautiful unit (on board DSP, built like a tank, I would hate to let it go). I don't suppose anyone has had similar problems and found a solution? Any thoughts would be greatly appreciated, jm1976
Try unplugging the power from the unit overnight, then plugging it back in. This might reset the internal IC control chips.
While it's not unusual for electronic devices to work for 20 or thirty years, it's also not unusual for them to quit working. It's twenty years old. Time for a replacement.
Unless of course the above advice works.
no matter how badly you'd want to keep it, but less-likely you can find even replacement parts for that.
To All Who Responded, Thx for your thoughts--- I have replaced the belts on an ES cassette deck and also the portable WMD6C, so I know just enough to be dangerous. Given that the C79ES is probably beyond hope anyway, I think I will do a tear down and see if anything pops out as a possible cause. There is a lot of cross coverage when it comes to Sony parts, such as power supplies, perhaps I will get lucky. JM76