Mostly dictated by age of machine - early Sony‘s were a bit of a nightmare, requiring a full setup When the laser was changed (I hate the CDP-101 for exactly this reason
) But all manufacturers quickly improved QC such that adjustment wasn‘t necessary on laser replacement. My CDIs use CDM9-Pro mechs - these are pretty much unobtanium nowadays. But CDM 9/44 lasers are easily transferable, and my spares are Kodak CD-Photo Players (on the basis this legacy tech was rarely used as a CD player very often, so lasers should be low mileage...plus, they’re cheap 2nd hand
).
Just to note: CDM9/65 (or 64?) lasers do not work in CDM9-Pro.
Most CDP faults nowadays are mechanical (laser or mech related), closely followed by PSU rail issues normally caused by failing electrolytics. All pretty easy to maintain to be honest, as long as you have a solution for when the laser does finally crap itself.
I very nearly bought a Sony CDP-X303ES (1 step down from their TotL 707 & 779 players) yesterday. I stopped bidding at CHF 80.- because when I asked the owner whether it ran without problem, his answer was that it read Discs and he hadn‘t tried any further. The KSS-272A laser units always read discs, but 99% nowadays will also skip on 2nd half of disc. After having to buy 3 donors before finding a decent 272a 10 years ago to fix a 707 I will not make the same mistake again