[1000mp] Reduced signal level on receive

[Tod Olson]

I noticed yesterday that there is reduced signal level [not zero signal
level] on RX with one of my FT1000MP¹s. Since I have two identical radios I
compared the signals from the same antennas applied one at a time to each of
the radios. The signal reduction appears to be present on all bands.

My next test will be to inject a known signal level from a signal generator
and verify that the signal reduction is essentially constant across all of
the bands. I expect that test to be positive ‹ essentially constant
reduction of RX signal across all bands.

>From the service manual I see that on the input to the BandPass filter board
there is a relay that connects the antenna to the output of the bandpass
filters when transmitting and connects to the RX input circuits when
receiving. In the receive path there is an unusual symbol classified as a
diode but which looks like back-to-back diodes. This item shunts the RX line
to ground. In the parts list it is identified as a Œsurge¹ item. I suspect
that when operating SO2R and at one point not having a Dunestar 600 Bandpass
filter in place, the voltage on the RX line from pickup when the other radio
was transmitting at 1500 watts on a different antenna may have stressed this
³surge diode². 

I wonder if anyone has had experience with this ³surge diode² failing. Is
the part still available from Yaesu? Etc.

Tod, K0TO