32K SRAM Uprade for the TNC2
-----------------------------
The TNC-2 was originally designed to use two (2) 6264 static RAM ICs, U24 and
U25, giving a total memory of 16K.  TAPR firmware revisions 1.1.4 and later
require 32K  of RAM.  In the MFJ TNCs, this change came in a later firmware
revision.  The TNC now uses a single 32K RAM chip.   The upgrade requires
a  slight modification to the PC board as follows:

1) Locate JMP12 on the board.

2) Turn  the board over  so that  the circuit  side can be seen.   There is a
trace connecting two of the three pads of JMP12.  Cut this trace.

3) Add a jumper between the center pad and the previously unused pad of JMP12.

4) Some implementations have a 3-pin header and shorting connector at JMP12.
If this is the case, you only need to move the header to the opposite position.

5) Remove the two 8K memory chips at U24 and U25.

6) Install a 32K CMOS static RAM chip, 43256C-15L or equivalent, at U25.  The
socket at U24 will not be used.


==========================================================================
Tucson Amateur Packet Radio Corp.
8987-309 E Tanque Verde Rd #337 * Tucson, Az * 85749-9399
Phone: (817) 383-0000 * Fax: (817) 566-2544

TAPR is a Non-Profit R & D Corporation
==========================================================================