I have a Radio Shack 3-in-one remote model 15-2147. I need to control a Magnavox TB110MW9 DTV digital to analog converter box. Radio Shack tech says the code is not built-in but surely there must be a code since it is a programmable remote. Thanks for any help.

No, there isn't.

Look at it this way, let's say there are 50,000 different remote control codesets out there, but an individual universal remote control only has enough memory to store, let's say, 1,000 codesets, the people who are making the remote have to make a decision on which codes to include. The first thing they do is sort out the codes by region, so if the remote is destined for the USA, they'll discard codes that are only used in Europe, Mexico, etc. Then they'll try and decide which codes are more popular, so the Sony, Toshiba and Panasonic codes will probably make the cut, but codes for lesser known brands may not. It sounds like the Magnavox code that you need just didn't make the cut.