TNC2.17 RELIABITITY MOD FOR TAPR-2's Thought we'd share a mod for the tapr-2's. (pk-80, mfj-1270, pac-com, etc.) We noted -5v problems, when using the 5 wire control mode of operation. (not noted when using x-modem programs) this mod not only improves the reliability of operation but also protects the I.C.'s using the -5 volts from being exposed to +5 volts do to a failure of the -5 volt regulator. The indication of failure is the dcd light flickers or stays on even when the radio is turned off. 1) Replace the 6.3 volt 1/4 watt zener whit a 6.3 volt 1 watt zener. (CR-6) 2) Install a 1N4001-1N4006 diode in paralell with C-10. (it may be installed on the bottom of the board the end of the diode without the bar is connected to the (-) side of the cap.) The modification seems to have worked very well on the 4 tnc's that we have installed it. It won't protect the tnc from all forms of damage but it should minimize problems in the -5 volt area. good luck. bob, nk8t (member, fara packet users group) ======= From: NK8T@NK8T Some MFJ-1270B TNC's may have the calibration and tx audio gain controls, (R-76 thru R-79) mounted incorrectly. As a result these P.C.B. mounted controls will have to be adjusted in reverse direction for proper operation. C.C.W. becomes C.W. and C.W. becomes C.C.W. The problem was first noted on unit S/N 01010124. The adjustment screws should be on the side of the control nearest the power off/on switch. If they aren't simply reverse the adjustment procedures with respect as to C.C.W. and C.W. BOB, NK8T =====