RA17 page 19

This is the 2nd Mixer. I almost forgot to take the ‘before’ shot; hence the resistor on the right. This is a particularly tricky circuit to work on owing to the two end-mounted inductors bottom left. Their presence makes the removal and replacement of the 1K resistor (bottom) and several other components very tricky . . . But not impossible. Keen not to incur the same spectacular burn out that I experienced with my RA17 I was opting to cutting the old components free then carefully unwinding the free ends from the solder tags. I found that the best way to achieve this was to heat the joint then grab the wire with hook-nose pliers and then just as the solder was almost solid, unwind it. This slightly unorthodox method allows you to remove the wire without incurring solder splashes.

I got a bit carried away and forgot to take the obligatory ‘before’ shot of the Crystal Oscillator; hence why there is only a nice shot of the Harmonic Amplifier. It was after refurbishing this section that I became aware that something was not right. The receiver sensitivity would fluctuate spontaneously. I hate intermittent faults! Sometimes it is a good idea to walk away and only return with a fresh mind . . . which is what I did. The root of the issue turned out to be C7, top left in the upper photograph. I was looking at it and noticed that someone before me had obviously been at it with a soldering iron. The PVC insulation on the wire to one of the terminals was clearly badly shrunken back. I gave the capacitor a tweak, or rather, I completely rotated it several times. This action completely cleared the intermittent drop in sensitivity. Past experience told me that some tiny shards of solder had been shorting out the vanes. This would not have caused any electrical damage but would have had a serious effect on the level of injection into the 30MHz LP filter.Then just to ensure it was clear, I gave C7 a good blast of compressed air.