Luckily, my IC-M700D came with a circuit diagram. The schematics of the IC-M700 can be found on the internet.
Studying both circuits, the following can be said (corrections made, due to an error in the Service Manual):
- the MAIN UNIT pcb of the IC-M700D is the same as the one of the IC-M700
- both sidebands are using the same oscillator
- two crystals are switched by means of 1SS53 switching diodes (a 1N4148 will probably do)
- the LSB crystal's traces are present on the D's pcb, so is the LSB control lead from the MATRIX (ending at Q334's base)
- the D's LSB crystal and surrounding bits'n pieces (a switching transistor(2SC3402), a varactor (FC51M), an inductor and some resistors) are not populated
- for LSB a
4.908MHz4.920MHz crystal is required
- the mode switch needs to be wired up correctly, there may be a further transistor (Q1210) missing on the MATRIX pcb, further, there could be a jumper somewhere...
and the corresponding IC-M700 circuit diagram
The question now would be, if there is any cheap option for the crystal. Well, I figure, we are lucky on that one... there is a cheap crystal for 4.9152MHz. I intend to open one up and
The plan now is to
Remark: Never trust a Service Manual!
Reasons: The filter center frequency is 9.0113MHz. The (USB) beat frequency is a mix of 10.24MHz and 4.908MHz divided by four, i.e. 10.24-1.227=9.013.
To get to the other side of the filter, the resulting beat frequency should be higher, i.e. 10.24-(4.92/4)=10.24-1.23=9.010MHz.
I should have seen that before going into penning down crystals, which was a good exercise however.
Now, I need to do both, grinding up, and pen down, when ground away too much crystal material....