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There is a voltage drop in diode mode with illumination.
Opposite the transistor, I'm not measuring any voltage drop on the diode using my multi meter but the esr meter is identifying the diode and measuring Uf=1.14v and C=18pF .
Upon rechecking the diode with the multi meter in diode test, I'm measuring a 2 volt drop which seems excessive.
-. A 4.7k resistor, with one end tied to +5V, the other end tied to the phototransistor's collector.
-. the phototransistor's emitter tied to the +5V return.
-. You may try other resistor values later.
Measure with a DMM the collector-emitter voltage, with different light levels, including as much darkness as you can achieve.