The other day I got hold of a Tait TB7100 1U repeater. I thought I might make a good basis for a MMDVM HotSpot or even repeater. Apparently the RX had a sort of a problem. Using the service manual I discovered that the TCXO for the RX was missing its power supply due to a removed resistor. After fitting in a replacement the unit worked ok with a testing configuration for a FM repeater.
So that would make a good hardware for a MMDVM HotSpot now. Some research on the Yahoo group revealed that you need to directly wire RX and TX audio directly to the two modules on the inside.
![Tait TB7100 with MMDVM mounted inside](https://www.florian-wolters.de/images/ac17a97c-4196-434e-81bd-3fb7c11e4449.jpg)
As my version did not have the built-in AC power supply there was enough room to mount the Raspberry Pi and the MMDVM modem onto the bottom of the 19” case. For power supply of the Raspberry Pi I used a 12V-5V DC/DC converter.
As it came down to wiring the MMDVM to the RX/TX modules I took another look into the service manual to identify the possible connectors. RX and TX module both have 15-pin D-Sub connectors (Auxiliary Connector SK101) that are wired to the SI board. The service manual lists the following:
![Axuiliary connectors on RX/TX module](https://www.florian-wolters.de/images/3efa7bea-1847-4bbd-9f48-c58c5e767080.png)
So I made the following connections (Pin numbers on the 15-pin D-Sub connectors of RX and TX-module):
Receiver
RX Audio --> Pin 13
RSSI --> Pin 6
GND --> Pin 15
Transmitter
TX Audio --> Pin 7
PTT --> Pin 1
GND --> Pin 15
During programming you need to configure GPIO7 as low active and to trigger the PTT.
![Programming PTT on GPIO7](https://www.florian-wolters.de/images/9ddbdef0-9cd0-4328-aff4-da7c45a7acd6.png)