burned! - Page 1
Forum section: electronics / beginners

author: orso
author_rank: Newbie
timestamp: November 16, 2017, 10:00:46 pm
content: Hi! Took this picture on my ECU board and wonder if its a burned out resistor.

author: Dubbie
author_rank: Unknown
timestamp: November 16, 2017, 10:07:15 pm
content: Looks like a zener diode.

author: Brumby
author_rank: Unknown
timestamp: November 16, 2017, 10:26:43 pm
content: My bet also. Zener diode in MELF package.IIRC, Dave is a fan of the MELF...

author: trys
author_rank: Regular Contributor
timestamp: November 16, 2017, 10:30:03 pm
content: Zener next to a wee resistor named Zoe, making fiends with him. They're holding hands.

author: helius
author_rank: Super Contributor
timestamp: November 16, 2017, 11:08:14 pm
content: Small glass tubes can be either neons, diodes or capacitors. GDTs (gas discharge tubes, for transient suppression) tend to be quite a bit larger.Here is a glass cap:

author: xavier60
author_rank: Super Contributor
timestamp: November 17, 2017, 01:28:11 am
content: Quote from: orso on November 16, 2017, 10:00:46 pmThe part might not be actually bad. It might be running hot normally.

author: Brumby
author_rank: Unknown
timestamp: November 17, 2017, 03:26:25 am
content: Quote from: helius on November 16, 2017, 11:08:14 pmTrue - but the internal structure plus the markings put the zener clearly at the top of the list.Quote from: xavier60 on November 17, 2017, 01:28:11 amI see some flux residue - but no signs of heat stress.

author: viperidae
author_rank: Frequent Contributor
timestamp: November 17, 2017, 06:10:02 am
content: Looks like conformal coating, not flux residue.

author: mikerj
author_rank: Super Contributor
timestamp: November 17, 2017, 08:21:44 am
content: Maybe I'm missing something, but why would you think anything is burnt out in the pic you posted? No obvious signs of heat stress anywhere.

author: trys
author_rank: Regular Contributor
timestamp: November 17, 2017, 08:38:42 am
content: I imagine orso saw the black band, and thought it looked like a little burnt out bit.

author: orso
author_rank: Newbie
timestamp: November 17, 2017, 02:08:13 pm
content: Yes, It looked burned in my eyes, I'm a noob when it comes to components and electronic engineering, but i'm learning (I'm a chemist). Did find some bad soldering on the board that I'm gonna replace. /Thank's for the help.

author: trys
author_rank: Regular Contributor
timestamp: November 17, 2017, 02:19:21 pm
content: Hey orso, in chemistry, very often if it's black it's burnt.Trys

author: mikerj
author_rank: Super Contributor
timestamp: November 17, 2017, 02:55:21 pm
content: Fair enough, I can see how you could think that if not familiar with that package. I don't think I've ever seen a burnt-looking glass diode come to think of it. They usually fail short circuit, though I have seen them light up inside, probably a bond wire glowing

author: macboy
author_rank: Super Contributor
timestamp: November 17, 2017, 03:20:15 pm
content: Definitely a normal looking diode in MELF packaging.I might be wrong, but in my experience usually diodes with a black cathode ring are just silicon diodes. With a blue or other color ring, they are something else like a Zener. So in this case my bet is not on a Zener as others suggested, just a common diode probably 1N4148 or so.

author: KL27x
author_rank: Super Contributor
timestamp: November 18, 2017, 04:44:48 am
content: ^I was curious about this. Maybe they are guessing zener just because of the 2k series resistor. That boosts the odds it's a zener, IMO. (Or maybe just happens to be a reglar diode used to make a reference voltage, lol).But in MELF, anyhow, all my zeners have a blue band, and the regular signal/rectifiers have a black band. (In the thru hole glass diodes, all mine have come with a black band.)

author: Nerull
author_rank: Frequent Contributor
timestamp: November 18, 2017, 04:53:48 am
content: There's another thing about zener diodes that can give people a shock - they light up. Not nearly as much as a purpose built LED, but "normal" diodes can give off light too. Zener diodes (or at least some of them) can give off a red color that almost looks like they're burning up.

author: floobydust
author_rank: Super Contributor
timestamp: November 18, 2017, 04:56:12 am
content: MELF's are terrible, they roll off the board during reflow. And they roll off your bench. And they roll on the floor. Crunch.

author: Brumby
author_rank: Unknown
timestamp: November 18, 2017, 05:10:10 am
content: Quote from: KL27x on November 18, 2017, 04:44:48 amHadn't really paid attention to this - but I just checked all my MELF zeners ... and, yes, they have the blue band.But I have seen MELF zeners online shown with black bands and with yellow bands. (But thatisonline)

author: KL27x
author_rank: Super Contributor
timestamp: November 18, 2017, 05:28:10 am
content: QuoteWhen I browse the parts on Mouser, some of the manufacturers have a drawing of MELF diodes that are square bodied and round only on the end. But whenever I buy them, they are all the same cylindrical thing. Is this rectangular MELF a real thing, or too good to be true?I tend to stick with MELF for zeners, anyhow, because it happens to be one of my known commodities. Some SMD diodes I have bought (without looking hard nuff), only to find they have stupid reflow pads that don't wrap around the sides, at all. And many of the ubiquitous SMD black epoxy packages have a stripe that is very hard to see. So for low current diodes, I like MELF for zeners. They are very easy to identify and to solder. The flux keeps them from rolling around, once I place them on the board.Never having to flip them over, this more than negates the rolling, IMO.