In article ,
J.B. Wood wrote:
Hello, all. Don't really have a repair issue but could use some
clarification from anyone familiar with the ca. 1989 subject device.
(The D-T2 is the model D2 with the addition of an AM/FM tuner.)

The unit uses 4 AA batt but can be powered externally. The DC input
jack on the back of the player is labeled for 9 VDC and the user manual
confirms this is the voltage that an external source should supply. The
AC adapter that was supplied with the player is a Sony AC-9W which
supplies 6 VDC vice 9 VDC. The Discman works OK with the 6V adapter but
the service manual for the model D2 (found a copy online) cites the
correct AC adapter as model AC-940, which is rated at 9 VDC output.

If the AC-9W provides regulated 6V (probably does) you should be safe.

The DC input probably uses a standard (vs. low dropout) voltage regulator
that does not kick in until the input voltage is 2.5V above the target
(i.e. 6V + 2.5= 7.5V). Hence the nominal 9V input.