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TNC2.8
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1992-09-15
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TNC2.8
b. Find some 4-40 or 6-32 threaded (preferably aluminum) spacers and
cut off a 0.30" piece. Use this threaded spacer as the mounting nut
for the 7805 on the back side of the board with a short screw going
thru the tab on the top side of the board. After you slide the
board into the cabinet, use a second short screw to "bond" the
spacer to the cabinet
The WB6RQN report on LM358=U8 problems in modem calibration is similar
to that experienced by the TNC2 "beta" group. The problem is that the
'358 is supposed to give a digital signal from the 2211 which is then
counted in software to set the frequency. But there was a tendency for
oscillations to occuras the signal went thru zero crossings, leading to
a bogey count. In addition to the 0.1 uf cap between pins 3 & 4 on U8, I
also found that replacing U8 with a TI TLC272 low-power (and slow!!!) op
amp which can be obtained at your local Radio Shack (part no. 276-1749,
$2.19) solved all my problems.
CONTINUED IN FILE TNC2.14