TCM3105 has not been manufactured in several years, so I decided to replace it with FX614 from CML Microcircuits in my TNC2.

For the first, I changed some elements on main TNC board. The basic is a crystal: FX614 required 3.579545MHz crystal, so I replaced an old 4.4336MHz. The next are AF input and output elements: changes depend of original TNC construction - may be any changes are not required. For the end, I placed two 8-pins connectors ('man') on main TNC board. The 'woman' connectors are placed on added PCB modem board. The normal IC Socket is too low and probably new modem board will be closely to elements on TNC board.

Pic1. FX614 modem schematic

New modem is made in SMD technology. It is quite easy. Printed board for SMD elements is difficult to paint manually, so I made it using photo method. More information about making own PCBs can be found in Internet. Look for the K5LXP or SM0VPO webs.

       
Pic.2 Printed Board                                      Pic.3 Component's Location

On the left side of the PCB (Pic.3) there is connector (two rows of 8 pins) to main TNC Board. It is only one element on the bottom side of the PCB. Two brown lines are jumpers. All other elements (SMD) are on the visible top layer.


Pic.4 Printed Board with elements

Zipped versions of pictures can be downloaded by clicking on the pictures.
If you have any question - send me e-mail