IC-706 has a problem when transmitting in FM (fix)

The defect manifests itself in the fact that after locking in FM mode, the IC-706 does not produce any power. At the same time, in other modes the station broadcasts without problems, moreover, reception works in all modes - including FM.

During a more detailed measurement, you will register full power when locking for a moment, and when checking with another receiver nearby, a very weak signal (carrier) frequency-shifted a few kHz to the side. The error is caused by the FM PLL at ( MHz, which does not hang, but oscillates. After mixing, however, the resulting product lies outside the pass characteristic of the filter. Therefore, the transmitted signal is sideways and very weak. How to eliminate this defect?

How to repair IC-706?

• Turn off the transceiver
• Disconnect all cables
• Remove the five screws holding the top cover (three on top, two on the side)
• TCVR turn towards you as in normal operation. The circuit board you see is the motherboard
• Find the 9.0115 MHz MF filter. About 9 mm from it is a tiny trimmer marked C267
• Now connect the power cable, the microphone and the artificial load with the wattmeter. Set the lowest power and try to lock. Probably no change has happened yet.
• Turn off the TCVR and gently rotate (by 10 degrees) the trimmer. Turn on TCVR and try to lock. If the performance does not increase, try to repeat it by turning to the other side.
• Do this until the performance appears. The setting is not critical.
• On the auxiliary receiver, check that the frequency matches and that the signal is not dragged 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 did not check it. The repair is not difficult, it is necessary to proceed with prudence and caution. I also read about a case where the trimmer was not sufficiently soldered to the PCB, so in case of instabilities it is worth checking this as well.