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)
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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
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