ECN Forum Forums General Topics of the Trade General Discussion Area Need help identifying diode

I will definitely post that image tomorrow. Calling it a night right now.

The chances are high that it's a 6.8volt zener.
Can you deduce anything from the associated circuit components? For instance it looks as though the three cathodes are connected together; is that point ground? Do the working ones have ~6.8v across them? Or are they perhaps across signal input lines as transient suppression?
Finally, (though should be firstly), have you tried calling the manufacturer? I've sometimes found specialist manufacturers quite helpful with technical queries.

Here is a more complete view of the board I'm working on:

Here is the identical sacrificial board that I attached to a piece of MDF and made more accessible for testing AFTER I replaced a diode that I believed was causing the malfunction:



This unit appears to be working fine. I have removed the touchpad and replaced it with various wires attached to a terminal strip. I can short the wires together which will cause the appropriate indicator light to come "on". Then I can cancel those same lights. Before I replaced the diode one of the "call" lights was always "on" and could not be cancelled.

When I power the board that appears working properly and measure the voltage with positive lead on the anode and negative lead on the cathode I get -3.8V on CR3 and CR2 but 0 V on CR1.

Contacting the manufacturer is definitely a good idea but without being a 100% positive I believe Dukane is no longer a supplier of this equipment. Most Google searches seem to result at a company called Crest. Their website shows older Dukane nurse call equipment but it doesn't look anything like the equipment I'm working on. This equipment is quite old. Still, it may be worth sending an email.

Oops. I guess I forgot to mention... The voltage drop measured across the diodes on the board that is not functioning properly is 0.17 V.

^^^ correction - that previous measurement should be "0 V".

If its any help, Dukane sold off the nurse call station division to this company in 2002 according to the Dukane web site

http://www.ascom.us/us-en/index-us/systems-division/ascom-telligence.htm#overview

"CR" means "crystal rectifier". An old name for a solid state diode, made from a piece of silicon or geranium. So it is a diode.

CR tends to indicate a diode and you seem to have proved it.