Glowing Zener Diode-Bad?

I've seen diodes for voltage regulation which look like small signal glass types, but actually glow red. Unless this diode is passing a large amount of current, I suspect it's meant to light up. Does it get burning hot? If so, then there's probably something wrong!

Dave

Some high end amps, & receivers, as well as rear projection T.V.'s have diodes to give visual indication that a certain part of the circuit is working, & has B+ power. Rono.

How do you know its supposed to be a Zener and not an LED? As Rono pointed out surface mount LED's are common on PCB's and are intended for the eyes of the service technician.

OK, I haven't seen an LED with axial leads either, but I bet that's exactly what you have there.

"JR North" bravely wrote to "All" (25 Sep 05 23:33:32) --- on the heady topic of "Glowing Zener Diode-Bad?"

JN> From: JR North JN> Xref: core-easynews sci.electronics.repair:343144

JN> I know all diodes actually emit photons, but this tiny glass Zener is JN> the first one Iv'e seen actually glowing LED red. Is it bad?

If it's hot "too" that is bad.... or not, get out the marshmallows! Seriously, perhaps it is a LED being used as a Zener. What is the voltage and package type markings?

Many zener types are encapsulated in black or painted, thus if they glow they aren't often seen. Basically many junctions can emit light and led's were an accidental lab find.

A*s*i*m*o*v

... I worked hard to attach the electrodes to it.

Does it have a reference designator silkscreened near it? LED's and Zener's often, but not always, use designators other than Dxxx or CRxxx. (LEDxxx, DSxxx, ZDxxx, Zxxx).

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