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

Závada sa prejavuje tak, že po zakľúčovaní v FM mode, the IC-706 does not give any power. However, in other modes, the station transmits without problems, and reception works in all modes - even FM.

In a more detailed measurement, you will register a very weak signal (carrier) with a frequency shift of several kHz to the side when locking for a moment and checking with another receiver nearby. The error is caused by the FM PLL at ( MHz, which does not hang up, but oscillates. However, after mixing, the resulting product lies outside the passband characteristic of the filter. Therefore, the transmitted signal is sideways and very weak. How to fix this error?

How to proceed with IC-706 repair?

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