Kenwood TR751E Will Not Transmit

 I will be honest, I am a Kenwood fan. Therefore, it was sad to see this little set only putting out a few milliwatts of power.

The first thing to suspect are the finals. Perhaps the antenna attached to the radio had a poor SWR or maybe it had been on Tx without an antenna at all.

The finals board on this radio is located at the back of the radio in it's own compartment. As the radio was putting out almost no power at all, the first thing to do was to check if it was getting a good signal in, from the pre-amp. The white connector on the top left of the picture is where the signal comes in. It was showing a good signal but a little on the low side of what it should be but a clean signal nonetheless. 

The next thing to do, is to check all the supply voltages to the board. Probing the white connectors on the top right of the picture showed that the -6 volt supply was missing. Now this is a common fault on these radios. The -6V is generated by a piggy back board soldered upright onto the main board.

It can be seen here, left of centre. The board cannot be sourced anymore du to the age of this radio. However, OZ1BXM has published a quick and easy alternative, made from a common components.

Due to the few components required, I choose to build this using through hole components, rather than etching a PCB.

The new board was installed and the finals came back to life again.

Another little set given a new lease of life.