New clues:

I started through the Section 5 adjustments and got to 5.2 step 7 with minor adjustments. Entering 13.5 GHz freezes the displays. They start to flicker at 13.370 GHz. I can no longer select any frequency above this.

The second observation is that the A9 reference resistor heat sink is too hot to touch. It shows Q1 and Q3 power TO3 devices? on the schematic but has 3 on the heat sink and shows 3 on the component diagram, fig 8-70 in my manual (83592-90079). Q2 & Q3 are identical but not directly connected together. Q3 is supposed to be a voltage regulator. Q1 is supposed to be the coil current driver. It is difficult to tell which device is making the heat. The parts list does not show any of the “transistors/regulators”. Q1 is marked 1820-0430, Q2 & Q3 are marked “ RCA 4-0080? HYP8432”.

Anyone familiar with this A9 assembly or have a schematic that shows the three devices?