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Further work I did tonight makes me almost certain that the PLL chip failed in the second upconverter. Pin 14 is the output to the microcontroller that goes high when the PLL is locked. It was high in the first upconverter but not in the second. Forcing that output high made the power light stay on solid, so it does in fact need to see both PLLs locked.
I was incorrect about the OP amp; it is configured with a gain of about 3 instead of unity like I said above. This is shown in the ADF4112 datasheet for use when a wide range of frequencies is required. This is also the reason for the 30V supply. It powers the op amp in both upconverters, so they can supply a relatively high voltage to the varactor diode. This also may be why I have read of others who had the flashing power light and fixed it by replacing capacitors in the power supply. The ripple was affecting the operation of the op amps and causing the PLL to go out of lock.
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Erich Loepke
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