Yaesu FRG7700
Written by Bryce Ringwood   

The FRG 7700 was manufactured from 1981 to 1984 in Japan. It covers 150 t0 30 000 kHz in 30 wavebands. The set doesn't use a computer, so there are no menus and other complications for people to get tangled up with. This radio, like its predecessors, the FRG-7 and FRG-7000 is easy to use and “if its there”, “you will hear it”.Yaesu FRG 7700 The audio quality is also very good. If you do see one of these sets advertised, be sure to thoroughly check it out before purchase, because repairing one of these sets is at best difficult and at worst impossible. Pay extra attention to the display – it should be clear and bright.

The construction is on a number of single-sided printed circuit boards. There are quite a few digital integrated circuits and a display-driver chip. The display is a standard gas-plasma display tube of the 1980s. The transistors used are Japanese, and some of these are dual-gate MOSFETs, so some of the components are very difficult to find.

The principle of operation is quite different from its predecessors, which used a Wadley loop. This set derives all the frequencies it requires from a single crystal and stabilises them using a phase-lock loop principle. If the set goes wrong, don't be tempted to fiddle with it unless you have all the correct tools, the service manual and the experience.

The set brought to me had very little wrong with it – the audio had either disappeared or else was motor-boating. There appeared to be corrosion around the audio chip pins caused by a leaky capacitor. The capacitor was replaced and all appeared well, but the next morning the motor-boating had returned. Once again, I removed the million or so connectors to the PC board. I replaced more caps and this time removed the audio IC and thoroughly cleaned the board. This cured the problem, but once again, the set fell silent. This proved to be caused by a defective solder joint on the mode selector switch. Movement of the switch probably caused the joint to come loose.

Once the set was finally repaired, it was an excellent radio – another one I was sad to return.



 
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