Don't quite see how a 7700 could be 10 years old. But it's getting close...
The 7000 was released prior to the 7700. And the 7000 was released in mid-late 1997. The 7000 was current in 1998. I don't exactly remember if the 7700 was relesed in late '98 or in '99.
Sony doesn't keep parts for their optical players as long as Pioneer does. And if you actually can get parts from Sony, damn are they expensive!

Sony much prefers that people buy new machine rather than fix them.
Pioneer on the other hand keeps parts in stock for a
minimum of 10 years after the last production year of the model. For instance you can still get a good amount of parts for a Laserdisc player that was last produced around 1979.

And they've been known to produce parts that they don't have in stock.
So if parts availablity worries you, stick with your DV-47A. You'll be able to repair that for many, many years to come.