Below are some hints and tips that I gathered when adjusting and repairing a number of KF161 units.

1. Rather than using wires or a pin header to fit the PCB daughter card inside the KF161, it would be better to use a stack header. Such a header fits nicely in the IC socket inside the rig and can be soldered directly onto the EPROM PCB. It'll cost you about EUR 3, but it saved the hassle of separate wires, damaged PCBs, damaged IC sockets, etc. Before soldering the socket, look carefully at the pins. The pins on one side are thicker that the ones at the other side. The thick pins should be soldered onto the PCB, whilst the thin ones should be pressed into the existing IC socket. Also note that the tick pins are longer than the other ones. Ensure that the PCB is soldered onto the pins as high as possible; otherwise it won't fit.
   
   
2. When aligning the HF output stage, please make sure that you first adjust it globally according to the template (the green transparent sheet inside the rig that shows all adjustments). If you don't do this, the HF output stage is likely to suffer from self-oscillating. This will happen after the first transmission. When you release the PTT, the output stage keeps oscillating, resulting in a 'deaf' receiver.
   
   
3. The 6 Watt output stage has been designed to deliver 6 Watt output. No more! Although the components are capable of delivering higher output, the output stage is likely to die before too long. The best method is to adjust the output stage's power supply to maximum,using R26. Next adjust the output stage for maximum output. Once that process is completed, turn R26 back until the output is about 6 Watt. A nice side effect of this over-dimensioned output stage is that it will survive a severe antenna mismatch (e.g. antenna not connected).
   
   
4. Throughout the KF161, many tantalum capacitors have been used. It appers that sometimes, shortly after powering up the rig, such capacitors can blow up, resulting in a lot of smoke and sometimes a small explosion. If this happens, don't worry. Just located the badly behaving tantalum capacitor and replace it. Please note that in most cases however, tantalum capacitor just cause a short circuit (rather than blowing up). Such faults are difficult to trace, as the capacitor doesn't show any external damage. I'm not sure as to why these capacitors are dying, but it may be related to their age and to the fact that they've been unused for quite a long time.
   
   
5. When aligning or repairing a number of KF161 units simultaneously, it is advised to have a known good one at hand. As the entire rig consists of a number of modules, it might be useful to swap modules in order to locate the cause of your problem more quickly.
   
   
6. My personal experience is that the PLL is easier to align when using an oscillator frequency higher that the receiving frequency (i.e. f+fi) rather than the more common lower frequency (f-fi). If you want to use the higher frequency mixing, some modifications to the main PCB will be neccessary.
   
   
7. Both the microphone pre-amplifier and the LF output stage have originally been adjusted for phase modulation (PM) rather than frequency modulation (FM). As a result of this the frequency response of the transmitter is increasing 6dB/octave, whilst the response of the receiver decreases 6dB/octave. A possible solution:
   • Short the jumper (near 'F') on the microphone pre-amp PCB.
   • On the audio output stage: Remove jumper 'P' and short jumper 'F'.
   
   
   
8. The microphone pre-amplifier has a LPF (low pass filter) with a cut-off frequency of 300 Hz. If you want to pass frequencies lower than 300 Hz (e.g. when using CTCSS), you should replace the combination C3/C4 by a single capacitor of 47µF (losing the junction with R2). Also, replace C7 by a 47µF capacitor. The cut-off frequency will now lie around 40 Hz.
   
   
9. The number of channels can be extend easily from the original 10 channels available throught the front-panel selector, by pulling some of the unused address lines low. The easiest way to do this is by heating pin 26 and pin 27 of the IC socket and removing them prior to mounting the socket. Connect pull-up resistors to both pins and wires to the tone buttons at the front (marked I and II). Convert the push buttons into switches by mounting locking springs.