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Substituting old diodes not made anymore?

bluebelly

bluebelly

Active Member
I have found a diode ( RD5.6EB3 ) that is bad on a DC supply board in an amplifier from 1985. I think I searched correctly but cannot find a match for that diode number. How does one go about determining what current production diodes will be substitutes for an old out dated diode? I believe all I have on hand are the 1N4007 diodes that I have used to replace selenium rectifiers with bridges.

Thanks,
BB
 
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It would help to know the model number and location on the board to know for sure, as a service manual with parts list may be available. However, I would suspect that it's a 5.6V 1/2W ZENER diode based on the number you listed.
 
Here’s a snapshot of the schematic. It is D859.
I was not getting the requisite 5.6 V off of this diode.
The parts list in the service manual lists it as a silicon NEC RD5.6EB3
 

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That is a zener symbol on there. I think Jhue is correct.

Digikey has many 5.6 zeners 1/2 watt, I looked out of curiosity

Something like 1N5232C-TR by Vishay ought to do nicely.
 
Yes, the funky angled ends of the line marking the diode symbol is used for zener diodes.
 
In summary, what are the required parameters that must be followed when replacing diodes? I fully understand capacitors now, such as it is okay to go with a higher rated voltage cap but not lower as long as the mfd remains the same.
 
bluebelly said:
In summary, what are the required parameters that must be followed when replacing diodes? I fully understand capacitors now, such as it is okay to go with a higher rated voltage cap but not lower as long as the mfd remains the same.
Click to expand...
Usually, voltage, current and Wattage. In switching circuits, switching speed is important (there are fast and ultra fast diodes). And in some applications, the voltage drop is important (usually when a low voltage drop diode was used).
 
In your case, the Zener Voltage and Power rating are the prime parameters. That Diode and Q854 form a series pass voltage regulator. The Zener diode along with the Base to Emitter Voltage of the Transistor sets the regulated voltage output of that regulator circuit.
 
Guys, thanks for all he input again! I am beginning to understand diodes now. I guess the Vishay 1N5232C-TR that "Warren-Oates" recommended will do. Unfortunately I had just ordered a bunch of parts from Digikey so it will have to wait a while before I make the order.

This diode went bad when I was probing around checking voltages on this board. I touched the positive leg of the electrolytic cap and it killed the power to the logic board and I heard the protection relay kick in. I do not think I slipped and let the probe touch the negative leg at the same time but who knows? I did go ahead and replace the 10 or so electrolytic caps on this board so it should be good to go now.


Thanks again,
BB
 
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