Once again, I appreciate the feedback.
I tried emailing a company to assist with identifying the diode and currently awaiting their reply...
Joe, I think you're correct about these diode being Zeners. I removed the diodes from 2 boards - one board was functioning correctly and the other was not. I checked the resistance of each in both forward and reverse bias polarity, I used my DMM diode setting to check forward bias voltage, and I set-up a simple circuit using a 1Kohm resistor, digital ammeter and variable DC power supply to see if they would conduct when reversed biased. Here's what I found (I numbered them 1-6):
- with the meter leads positive to anode and negative to cathode all diodes measured approx. 2 Mohm.
- with the meter leads positive to cathode and negative to anode the resistance varied greatly
CR1 = 15 Mohm
CR2 = 6.5 Mohm
CR3 = OL
CR4 = 42 Mohm
CR5 = OL
CR6 = 26 Mohm
- using the diode setting on my DMM all diodes tested good
- using the circuit for testing if they would conduct when reverse bias all diodes began to conduct at approx. 6.8 V
Hopefully this information further proves that they are in fact Zeners. Btw, on the circuit board all 3 diodes anodes connect directly to the row of capacitors. The cathode of CR1 connects directly to the collector of Q1. The cathodes of CR2 and CR3 connect directly to the cathode of an indicator LED - one for each of the two "call" lights - as well as connecting to an IC on the second circuit board through the ribbon cable.
