Back into this thread after a few days hiatus spent playing with non-ham-radio things.
Since the transceiver's history is unknown, the first rule of troubleshooting comes into play: "Assume nothing". Set the two reference oscillators per the Technical Manual. Then examine the behavior when on the Gen VFO...did it change?
In terms of modifications, there are three potential classes here: Those which Yaesu published or offered (including the General Coverage RF Unit module), those which the Fox Tango Club and affiliated persons published...and those which never were documented, were partially finished, etc. At some point in the past, the transceiver might have had a homebrewed/undocumented modification designed to accomplish a specific objective other than enabling the Gen VFO to transmit. Going back to the Balanced Modulator and other mixer circuits: After verifying reference oscillator settings, the next thing needed in this area is to confirm proper operation at the circuit on both Ham and Gen VFOs when in USB and LSB. This will give potential insight for the next part of the process.
With an accurate frequency counter, look at the output of Q4007 (2SC535A) or the input of Q3009 (MC1496P; the Balanced Modulator). Do so in USB and LSB when in Ham and Gen VFO mode. Referring to the data in the Technical Supplement, one should see signals of 8984.5 or 8990.5KHz (mode dependent) at these points. What is seen here?
73 - Fred, N8YX
