SACD Player Won't Play Hybrid SACDs

A few years ago I purchased a used Sony SCD-C555ES SACD changer. I bought it to use essentially as a CD player run through an external DAC. I have about 500 redbook CDs. A couple of days ago I bought my first SACDs and began playing them. Everything worked fine until tonight. For some reason, the same SACD hybrids that played fine several times will not now play in SACD mode. I get the message "Not Hybrid" and the player defaults to CD mode. I toggle between "Multi and 2 channel" and I get the message "Not SACD." Any ideas?
Not an uncommon problem with the older Sonys. The laser could need an alignment. I believe there is a diagnostic procedure for doing this. Check around the web. I found this-

Resetting Operation at Power ON
If the power is turned on with a disc loaded in the set, a sequence of operation as shown below will be performed.

(The operation varies depending on the type of disc) Condition: continue mode
1. Sled reverse move (sled in)
2. Disc detect
3. IC setting for SACD
4. Servo error signal offset auto adjustment
5. Spindle kick for LD on
6. LD on
7. Focus search
8. Focus servo on
9. Spindle kick
10. Spindle servo on
11. E-F balance auto adjustment
12. Tracking & sled servo on
13. Focus bias auto adjustment
14. Focus servo gain auto adjustment
15. Tracking servo gain auto adjustment
16. Jump to lead-in area
17. Read TOC
18. Auto play (track No.1)
Thanks for the info, Chayro. I wish I knew what it all meant. However, I'm certain the problem is not an alinement or cleaning issue. Over the past few days I have done some "testing." When the player has been turned off and sits over night or is turned off for a while, cools down and turned back on, it plays fine for a while. It correctly reads any combination of SACD and CD disks that are loaded into the changer. However, once the unit is on for period of time (give or take 2 hours), it stops reading SACD and will only read the CD layer. It won't stop reading SACD midstream during a disk play. Once it recognizes SACD, it will play the disk to completion and then stop SACD recognition on subsequent disks.
A few yrs ago, the unit was modified by Matt Anker of SACD Mods. He said the unit would run warm and it was normal. The unit played fine until recently so, I don't think the problem is related to his mod (which had nothing to do with the actual disk layer reading). I tried to locate Matt just to run the issue by him, but he is no where to be found.
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On my sony 5400, you can only play sacd in sacd mode with the internal dac. The digital output only works with redbook.
Sounds like weakening laser/read - lifetime is about 2-3years. Change the optical
assembly and you should be fine. Can be had from e-Bay for around $30-60 depending
on models.

My old dCS was fitted with Sony's SCD555ES equivalent, and I had to change them out
(optic assy.) once every 2-3years. Basically similar problems you encountered.
I dropped the SCD-C555ES off at the local Sony authorized repair shop. The place has an excellent reputation and does service work for just about all brands. The problem is the optical assembly. They're waiting for the Sony part to come in. Should be good to go.
Jjpeepers, good to know.. However if you plan on keeping the player for long, it is advisable to keep another sealed optic assy. as spare - it is getting scarcer by day. Depending on humidity, the problem could be an unpredictably recurring one. With Part at hand, should take no more than one hour to have it professionally replaced.

*For your easy referral, Part is : Sony, Device Optical, KHM-230AAA
Thanks for the info. Some problems have developed in attempting to get my unit repaired. There are now apparently 3 part numbers associated with KHM-230AAA. The original part # was 8-820-132-02. That was replaced by 8-820-132-03. The repair place ordered this part. It arrived, but was defective and was returned and another one ordered. Three weeks have passed and the part has not come in. Apparently, this part has been replaced by 8-820-132-09 and even this may no longer be available.
Is anyone familiar with 8-820-132-09 and is it now the "new" part for the SCD-C555es?
One last try. The first replacement part (from Sony) did not work. I purchased 2 replacements from someone in Taiwan that, based on various sites and blogs, is the go-to guy for laser assembly pickup replacements. He gets very favorable ratings and was certain the laser would work for my SACD player and all the ones that used that particular laser. The first one did not work. I'm getting ready to drop off the remaining laser to the repair shop.

There is a "solder blob" that needs to be removed from the assembly for installation. The repair person was well aware of this and properly removed it on each laser. Is there something we are not doing? It seems a bit crazy that none of the replacement lasers work.
Try checking the flexy-ribbon cable running from main to optic assembly board.
Occurred to me once where new optic wouldn't operate, and it turned out (after thorough
testing) one channel amongst six of what appeared to be still perfectly fine cable was bad.
After flexy-cable replaced, everything was good.

*Suspect also other connections that are possibly susceptible/get in the way/affected over
long haul when tray of disc travels in-out, or one that needed plug/unplugging when
technician is replacing the assy.
unfortunately, "years" are centuries in digital. Unless you paid as much as a porsche for a cd player (I only paid as much as a hundai), it usually doesn't pay to repair them. Doesn't pay means alot of different things. To me, it means the inconvenience isn't worth the aggravation with the reward being listening to the same old cd technology. I buy my player form a dealer and he handles everything, and when its so bad that I cant repair it - or it ain't worth it - time to trade up with my dealer. You get a new car every few years... do the same with your cd player.
Agree with Mr_m and Cerrot..
Unless it has a sentimental value of some sort, guess it's time to move on.
But do give 'em that one last try! ;) Good luck.
The reasons I want to hang onto this player are because a few years ago I had about $800 worth of mods done by Matthew Anker of SACD-Mods, it's a solid well built unit and it is an SACD changer. The player sounds great when it works and there ain't no more SACD changers being made. I like the convenience of a changer so, I want to try and save it.
The individual that I bought the laser assemblies from is going to replace them. This for sure will be my last try.
jjeepers did you ever get resolution? I have the same problem it still sounds nice in straight cd as now using an out board DAC. Don't know if I should move on or try and fix it?  Thank you
I miss Matt Anker and those other modders from the mid-2000's.
Hope you guys get your spinners fixed.