Blue striped Diode

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Blue striped Diode

Post by DocReef » Sun Jan 19, 2014 6:58 am

I'm looking at an old Slot Machine circuit board which has two(2) blue striped glass diodes on it and one of them is broken.
The only numbers I can see on the board are: 94014-MAIN3 and a tag with '96-4 Rev.1.

Can anybody give me an idea of what the blue strip means (signal diode, zener, etc.) on the diode?
I have no schematic and can not see any markings/numbers on the diode.

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Re: Blue striped Diode

Post by dyarker » Sun Jan 19, 2014 11:50 pm

The band on a diode indicates the cathode. The color of the band doesn't indicate anything.

Any numbers/letters printed on the diodes?
Dale Y

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Re: Blue striped Diode

Post by dacflyer » Tue Jan 21, 2014 9:30 am

if it is made of glass it is possibly a signal diode, or possibly a geranium diode.
then again possibly a zener..hard to say..

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Re: Blue striped Diode

Post by haklesup » Thu Jan 23, 2014 9:14 pm

you can measure the forward voltage on the good diode using an appropriately equipped DMM and that's a good starting place if the spec is important. Slot machines don't do much analog stuff so unless the diode is in an audio or wireless radio, it's probably being used as a rectifier. Your best clues are the function of the circuit the diode is in. In many cases, diode specs can be very flexible as long as you cover the minimum requirements and try to match the Vf (Rf which can be tricky to measure accurately without a curve tracer and AC characteristics might be unimportant in some applications). A diode used to make a voltage reference in a precision circuit or a high speed application for example, would be the hardest to substitute

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Re: Blue striped Diode

Post by Lenp » Sat Jan 25, 2014 8:38 am

Hi darkyer
Like said, being that construction it is probably a low current or signal diode. I would doubt it's anything other than silicon since that is the most common, but remember that germanium is light sensitive and are near always dark colored, so the mix gets thicker. Diac's are often funky marked but are usually clear glass. It sounds like the diodes are house marked, and not marked with standard nomenclature.

If the machine powers up, maybe you can measure the voltage drop and in/out on the other similar diode for clues. Look for low voltage rated capacitors associated with the diode for other voltage clues if it is a zener.

A variable power supply, a dropping resistor and either a meter or a scope might clue you as to if it's a common diode, or if it behaves like a zener or diac by measuring its knee or avalanche voltage.
If you had a curve tracer, and well, really, doesn't everybody :???: that would tell lots more!

Worse comes to worse, use a 'try piece' :sad:


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