Ok, I found a little time to hook up some more "test point wires". The results are confusing me. (Like that should be a surprise,...)
Measure the DC voltage at pin 2. The DC voltage at pin 3 has to be ~0.7V below the voltage at Pin 2.
No, there is no DC voltage at Pin 2, or Pin 3 And the AC output at Pin 2 is smaller even than at Pin 3.
As a reference you could also check the DC levels at the pins of the other uPC1037HA chips (IC5 in the main unit, IC16, IC17 in the PLL unit) although they don't have identical supply voltages.
Looking at IC5, it seems to have no DC present at Pin 2 either. And Pin 3 is just plain weird,... there is about a -.2 VDC present there with the radio "on".
With the power supply active but the radio power switched "off", there is a +.4 VDC at IC5 Pin 3! If the power supply is then turned off, the voltage drops, looking like a capacitor discharging.
Both IC5 outputs show a carrier of about .1 V peak-to-peak. They do not seem to change perceptively when toggling to Tx or applying modulation.
any DC voltage on pin 6 ?
No, there is no voltage at IC6 Pin 6 (the bypass line). It is at ground potential. But it was still a good idea to check that off!
I'm clearly not understanding this circuitry, but wondering if it would be a worthwhile experiment to SWAP IC5 with IC6. If the symptoms remain the same, it would indicate that the problem lies elsewhere, but it they
change at all, it would tell me I'm still dealing with a defective new part.