Replacement for that item is not critical, just so you know. As long as the specs equal or surpass the replacement, most any NPN transistor will work in that application. Talking about collector current (amps) and collector dissipation (watts). So if you have a transistor in your stash, just check the datasheet and see if it will work. Even if it's insufficient, if it's expendable, you can substitute it just to see if your old one was faulty. Even if its specs are not up to snuff, it should work for a short time. If the specs are substandard, I would not keep it in there though, more for just to see if it is your issue.
BTW what is ohms reading (powered off of course) from E@Q603 to ground?