Identifying Diodes

A

Aethelflaed

New Member
Hello Everyone,

Brand new member here and I'm looking for some help identifying two diodes. I've done a bunch of googling and I'm just not completely sure what I am looking at.

The whole project is the igniter from a 1984 Yamaha XJ1100 Maxim motorcycle. I'm been working on it all summer and everything is done, less the no start issue. I've run through the service manual flowchart and the final step is replace the TCI (igniter). This is a problem as those haven't been produced in a decade or two. There are new old stock ones on eBay but $400+ is a bit much.

I'm taking a crack at fixing one of the two I have in my shop.

Diode 2 and Diode 3 broke while I was removing the board, but they are identical to Diodes 1 and 4.

Diode 1 is a glass body, orange with a green stripe, it tested good with a multi-meter at 0.568v. It is identical to Broken diode 2

Diode 4 is a glass body, orange with a black stripe, it tested good with a multi-meter at 0.577v. It is identical to broken diode 3.

From what I found I think they are Schottky diodes but I just don't know enough to be sure, or what value I need.

I would appreciate any help you can give me.

Thank you.

 
I'm guessing it's a fairly standard rectifier power diode from the early 1980s. The glass body transfers heat better and can handle higher heat than the plastic body diodes. The diameter of the leads hints to a multi-amp rating (that is, it's not a small signal diode like a 1N4148.

Look carefully at the sides of the diode. D1 appears to have printing in green ink on the far side in one photo. Use your camera zoom or a magnifying glass to read the text. That should be the part number.

If you cannot find the part number, I'd try a 2A glass body rectifier diode.

The variation between your diodes is in the "normal" range. They are essentially the same. 9mV is rather small. A diode's forward voltage will change -2mV/°C temp increase. So, even if the two diodes did happen to have exactly the same Vf, holding it in your hand could warm it slightly and change the Vf.
 
Hi,

When you measured the voltage drop, which way were the leads connected ... that is, what was the polarity of the voltage relative to the stripe?
In order to confirm it is a rectifier diode you should note that the stripe would be the cathode and that would be most negative when you see a voltage drop of around 0.65 or so. If that's not the case, it could be a zener.

Also, you should specify the current at the time of the measurement. This is best done with a resistor and power supply and digital voltmeter.

It's probably a rectifier diode but it's also good to know the circuit that it came from. Rectifier diodes are slow so if this is a circuit that needs a fast diode, then it has to be a faster diode.
 
Like others say, I suspect they are regular diodes. Not likely to be a Zener, as there is one on the board labeled "ZD1" instead of "D" (ZD near R8 on left side of board picture). Thus these are just "diodes" of some type.
 
Hi ZipZap, MrAI and Sagor,

Thank you for the help. I will de-solder and remove the good diodes so I can check for markings. It's already broken so I'm not risking anything. I'll take some better pictures when that's done. I don't think they are Zener as the Zener on the board was specifically marked.
 
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