How to restore factory defaults on SIR T451 settop box?

Previously worked fine for all channels. After blundering through set tup menu, auto tuning ignores each local subchannel i.e., 5-1,5-2,5-3, and instead selects the ZERO of each channel group, except 11 which it cycles through (so this is not an antenna problem). 11 must have escaped whatever error I committed. There is a service jack on the rear panel. Possibly this permits diagnostic checks or restorin factory defaults.