The trusty old Icom IC-751A recently developed a strange buzz on transmit.
Most audible on SSB, and less so on FM. Time for an alignment check and obviously
looking into this fault. At first sight it appeared to be the dreadful VCO problem or
some HF getting into the modulation amplifier. The general specification check
turned out to be ok, so did the AF path of the modulation amplifier.
Well, sometimes it just takes a bit longer until the penny drops, once i realized
how it gets into the RF signal, it was quite obvious where it comes from.
In this part we show some of the alignment test procedures, highlight some errors in the
factory service manual and finally the reason for the buzz.
Next part will be more repairs and final test.
Please watch my other Ham Hadio related videos, just look for the Ham Radio playlist