said by toro:If it's several years old the power adapter may have failed. Many times the capacitors inside swell and while the adapter still provides some power, the voltage drops below the value required to run reliably.
Yep. I should have thought of that. My brother's SPA2102 went out this weekend. It kept dropping registration on both lines -- took about a minute to do this after powering up. He had an extra power supply on hand, so I told him to try that -- it's worked fine ever since. He had been having intermittent problems with it for a couple months.