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I'm using the 3325B service manual on Keysight's website from March 1990. Specifically the schematic right after page 8-F-4 which is Figure 8-F-2 Fractional N Analog A21 on PDF page 130. CR3 and CR4 are facinging each other at the end of the Phase Comparator and Integrator. I did get Anode and Cathode reversed. The cathodes connect while the anode of CR3 connects to Q3 of the Phase Comparator while CR4 anode connects to several things including R71 from the Integrator.

For CR3, the anode connects through Q3 and Q4 as you say. The most direct route to power is the collector-emitter junction of Q3 to?+5V (I called it?+15V as my copy is very hard to read).? Q3ce does have a resistance but in the worst case (failed transistor) it will be a direct short to +5V. The most direct path to power for the cathode of CR3 is the source-drain junction of Q18 (I think) but that is only?+V which CR3 will block. The next best route is through the source-drain junction of Q10 (I think) and then through the dual collector-emitters of U2A then U30A (another guess) which is a 1150 ohm resistor to -15V. So the worst case looks like?+5V -|>|---/\/\/\/\--- -15V. That is 20V across 1150 ohms or 17.4mA. To calculate the power dissipation across CR3 (not the power flowing through CR3 which is 20V * 0.0174A or 348mW) we need to know the voltage drop from 17.4mA at the operating temperature of the diode in the worst case scenario. This is different for each diode so we need to pick one and see. Let's use the 1N4448. It is not the best choice but has the most detailed datasheet. We will use a reputable version from Vishey. The rated power dissipation is 440mW @ 45C which is the maximum amount of heat the diode can eject continuously in normal circumstances. We only care about power that is converted to heat which comes from some kind of internal resistance. The resistance comes in the form of a voltage drop across the diode. You often hear that silicon diodes have a 0.6V drop and Schottky diodes are somewhere around 0.35V but that number changes with current and temperature. Page 2 Figure 2 of the 1N4448 datasheet is a forward current vs forward voltage graph. Forward voltage is the voltage drop at a given forward current. We can approximate 17.4mA with the 1st line above 10mA. We find the forward voltage drop to be about 0.8V. Now 0.8V at 17.4mA is 14mW which is the worst case power dissipation from CR3.

Doing the same for CR4 we will use the same cathode connection of -15V through a 1150 ohm resistor. For the anode side we follow R72 (1k) through W2 (assuming jumpered in the test position which is a valid?non-fault condition) past TP10 through the collector-emitter junction of Q9 to +15V. If Q1 FET were to fail we could also see a direct short to +15V. So max operational current is 30V (+15 to -15) through 1150 ohms (fault) or 2150 ohms (non-fault) for 26/14mA. The forward voltage drop of 1N4448 at 26mA is maybe 0.85V. 0.85V at 26mA = 22mW power dissipation.

Modern silicon diodes exceed the specs of many of these old Schotkky diodes when they were used mainly for their low forward voltage to achieve a lower power dissipation. I hope that helps.