Diode ID

[ahakman]

Can anyone help identify these diodes? I have a bunch of examples of what I think are the same diodes, but they have such minimal markings on them, it's hard to tell.

The bodies are really short, have a blue cathode marking, and blue "4" and a letter. On 3 different boards I have, the letters are different, but otherwise they all look the same (and I'm guessing they are the same component) - the letter is a date code or factory code or something?

On one board, they're labeled "4 K", on another board that's exactly the same, but probably produced at a different time, they're labeled "4 A", on a slightly different board, but manufactured by the same company in a very similar device, they're labeled "4 D". These are probably designs from the late 80's or early 90's, with build dates in the early to late 90's. The middle picture is a little blurry - my phone wouldn't focus properly. It's very clearly an "A" on that one. I don't have a picture of the "4 K" variety, but they look identical, except for "K" instead of "A" or "D"



Anyone have any ideas? Are they just 1N4004's??

[madires]

Used for a bridge rectifier? What is the diameter of the diode's body?

[ahakman]

No, not used as a bridge. The main bridge rectifier is a large integrated one mounted to a heatsink.

Some kind of small signal (to medium signal) diodes. These boards have a mix of diodes on them - there's typical glass diodes, but most (but not all) of them are labelled as ZD###, so most likely zeners. There's these, and there's some other glass diodes that are marked as normal diodes on the silkscreen designator, that have a white and green stripe on the glass package.

These ones are 2.5mm dia x 2.8mm long measuring just the body. The legs are 0.6mm dia. The lead spacing (as the leads are formed) is about 10 or 10.5 mm

The ones that need to be replaced need to be replaced because the electrolyte from leaking capacitors ate away the legs of the diodes, not because they failed (well, one failed, but that's because a large zener went short that was very close to a leaking cap)

Also, the forward voltage drop is 0.471 - a bit lower than a normal silicon diode - Schottky? Germanium??

[madires]

Assuming a test current of 1mA, a Vf of 0.47V would be too high for a Germanium diode. Maybe some old Schottky.