The defect manifests itself as such, that after keying in FM mode IC-706 does not give any power. At the same time, in other modes, the station broadcasts without problems, moreover, reception works in all modes – ay FM.
In a more detailed measurement, you will register full power for a moment when the key is locked, and a very weak signal when checked with another receiver nearby (they carry) frequency shifted a few kHz sideways. The error is caused by the FM PLL on ( MHz, which does not hang up, however, it oscillates. However, after mixing, the resulting product lies outside the permeable characteristic of the filter. Therefore, the transmitted signal is sideways and very weak. How to remove this error?
How to proceed?
- Turn off the transceiver
- Disconnect all cables
- Remove the five screws holding the top cover (three on top, two from the side)
- Turn the TCVR toward you as in normal operation. Printed circuit board, which you see is the motherboard
- Find the MF filter 9,0115 MHz. But 9 mm from it there is a tiny trimmer marked C267
- Now connect the power cable, microphone and artificial load with wattmeter. Set the lowest power and try to lock. Probably no change has happened yet.
- Turn the TCVR off and rotate gently (O 10 degrees) trimrom. Turn on TCVR and try to lock. If performance does not increase, try to repeat it by turning to the other side.
- Here's how to proceed, until performance appears. The setting is not critical.
- Check on the auxiliary receiver, whether the frequency matches and the signal is not swept away during modulation. It must be clear and clean.
- If so, close the transceiver
The service manual states, that the voltage at the control point should be 1.5V, but in my case i didn't control it. The repair is not difficult, it is necessary to proceed with prudence and caution. I also read about the case, that the trimmer was not sufficiently soldered to the PCB, so in case of instabilities it is worth checking this too.