MASTR II to TNC 2 Connection Chart
Jon Adams NW6H / Greg Noneman WB6ZSU

Pin #
Pin Function
Connect to
Pin #
2 shield Mic -   2 Return
4 brown Mic +   1 Audio Out
8   F1 Select GND    
19   Preamp Out   4 Audio In
21   Cont A- GND    
24 red/white   +12V    
25   PTT   3 PTT
27 brown Spkr Lo *    
28 green Spkr Hi *    
29 yellow A+ +12V    
30 black A- GND    
39 orange A+ +12V    
40 yellow A- GND    

* Connect a 5W, 8ohm resistor between these two pins to provide a load to the MASTRII audio amplifier. Can also take this opportunity to add a speaker jack to cable end so that you can hear the audio as required.

The MASTR II 35W version has a recurrent problem (at least the dozen or so I have played with) with the transmitter power control hybrid. Generally, the hybrid appears to fail and the output power goes to zero because the hybrid shuts off the PA. The suspicion is that the hybrid detects VSWR and thinks that something's wrong and so shuts down the PA to protect it. We've seen them come back to live spontaneously, so it's not the most reliable thing.

The other problems we've noted with the MASTR II include failures of the transmitter multiplier stages and one time a dead receiver.

One other thing - we use the VHF-High band high-end MASTR IIs for amateur service. These units come from the factory set up for running from about 150 - 170MHz. At a minimum, the tanks in the transmitter stages need to be padded in order to get the radio to tune properly. Greg has actually gone in and redone the coils per GE specification and that works very well. I will publish the mods when I can find them.