[G0HZU_JMR]

Hi Steve, I'm not familiar with the FT767 radio but I had a quick look at your schematic and I can guess a few things.

Probably the most significant thing is that it looks like this radio is meant to be deaf across 0.5-1.5MHz as it has a resistive (21dB?) T attenuator ahead of the relevant filter section using series resistors R176 (470R), R177 (100R) and R178 (470R).

There has been a lot of misinformation in ham circles about diode switching in radios like this and there seems to be a bit of a fad for replacing the factory diodes with PIN diodes. There have been lots of arguments over the years if PIN diodes offer any benefit (in terms of IMD) over regular silicon diodes.

However, one way to boost the distortion performance of a diode switch like this is to raise the impedance of the switched filters well away from 50R. This reduces the RF signal currents in the diodes. The diodes can be thought of as non-linear resistors and it makes sense to minimise the RF signal current through them.

Therefore, I think the designers of your FT767 have chosen to do the Rx preselector band switching at an impedance of 450R. The writing is fuzzy on your schematic but It looks like there is a 9:1 transformer at the input to these filters.

This means the T attenuator has been designed to add 21dB of fixed attenuation inline for the 0.5-1.5MHz frequency range. These filters do appear to have been designed as 450R bandpass filters. The 21dB attenuator is probably there on purpose because this is the MW band and there could be huge signals on this band at night.

Therefore, I'm not sure if your radio is faulty. How deaf is it on this range?