FT-980 no power out in HAM mode
After? many years iddle I switched on the FT-980 and it did not transmit.
To make a long story shorter, the transmissión is inhibited if a trasverter is used or in General mode. It does it cancelling voltages to PA bases (PA cut).
Q01 in RF unit makes the control job and Q03 acts as a switch.
I measured 5V in its collector and 3V in the emisor output (should be 13,5V/13V).? I thought upwards the relay RL01 had a bad contact. It changes Rx/Tx 13,5V or 0V
But then I measured only 20 Ohm load in the output of Q03. So suspicion changed to PA. 600mA is far too much for controlling base bias.
The PA was receiving from RF unit 3V instead? of 13,5V for the bias internal regulacion. 13,5V>8V>1,3V. The PA includes a 7808, plain diodes? and zeners for the job.
PA is full of tantalum capacitors. 2 outside in fan control and 7 inside.
I opened all but it is beyond my capabilities to desolder heavy things in PA to access the capacitors.
Maybe I can cut the first capacitor and place it in the RF unit output to PA and maybe even the second capacitor after the 7808. But it is impossible for me to go beyond that. Most of the tantalum capacitors have ceramic in parallel... maybe I can feed PA and bias control with 13V and start cutting tantalums until I find a reasonable iddle courrent. Distorsión? Maybe if not enought iddle...
I have not read about a similar problem. Waiting what to do... Maybe move the FT-980 where it has been the last 20 years. It is a good receiver. I replaced the Murata 2,7kHz 455kHz Width control with a Quartz filter 2,1KHz and now it is very effective.
I plan to test the PA outside the 980, at least voltages and intensities to confirm the tantalum disaster.
73
