1. Remove jumper from all pins of JMP 9. Jumper will be used later in
this modification at JMP 21.
2. Remove IC U40. After the modification is complete, place U40 into a plastic wrapper
and tape inside the front face-plate for later use if the node is ever returned to
normal TNC service.
3. Remove jumper from JMP 15.
4. ADD A JUMPER at JMP 16 (use jumper from JMP15).
5. ADD JUMPER at JMP 21 (use jumper from JMP 9).
6. Remove the TNC (stock) EPROM at IC location U23. CAREFULLY install your
new X-1J4 EPROM into socket at U23. BE SURE ALL PINS ARE INSERTED INTO THE SOCKET
(be sure there are no bent pins). Pin number 1 is NOT left out of socket as it was
with earlier revisions of this TNC. This modification applies only to MFJ-1270C
"Rev 11."
7. Cut trace at JMP "X" Notice that tiny traces are close to JMP X: DO NOT CUT any
other trace. Cut ONLY the trace between pads of JMP X. Use extreme caution when
cutting.
NOTE "A": The photo shown above is an MFJ-1270C/Rev 11, and has the "MFJ-9600," (9600 baud)
internal modem installed. The same mods apply to both 1200 and 9600 baud MFJ-1270 "C's."
NOTE "B": Cutting JMP "X" is optional; If you are concerned with the node hearing
itself and listing its own call and alias in its own node list, then CUT JMP "X".
A problem occurs when JMP "X" is NOT cut and the node lists itself in its own node
list. A user might inadvertently issue a connect request to the same node and
find that they are connected again (locked) into the node. They may be required to
issue the "BYE" command two times to be released.
NOTE "C" All MFJ-1270C/Rev 11 built after July 1996 have R14 & R15 installed. If they
are not installed in your MFJ-1270C/Rev 11, they will not cause a problem unless you
plan ot use the TNC in a node gateway, between two frequencies or in a node stack with
a diode matrix. If R14 & R 15 are missing and your node IS TO BE USED between two
frequencies or in a node stack with a diode matrix, then you should continue to steps
8 and 9.
8. If TNC is to be used as a GATEWAY between two frequencies or baud rates, insure that
R14 & R15 are installed. If they are not, remove the PC board and add R14 and R15.
R14 and R15 are 100 ohms @ 1/4 watt each.
9. To remove the PC board, remove the front face-plate (2 screws), then remove the screw
that attaches Q3 (regulator) heat-sink to the front of the TNC. Next remove the four
(4) screws which hold the PC board in place. The locations of the screws are shown in
the photo as a red circled "X" symbols.
