MELF Diode with Colour Ring  - Page 1
Forum section: electronics / beginners

author: 2X
author_rank: Frequent Contributor
timestamp: May 25, 2019, 05:54:09 pm
content: Hello, I measure the below diode and it is short circuit at forward and reverse polarity. Does anyone knows what diode is in order to replece the old one?

author: jmelson
author_rank: Super Contributor
timestamp: May 25, 2019, 06:53:30 pm
content: Z3 makes me think it must be a Zener diode. Can't help more than that.Jon

author: bob91343
author_rank: Super Contributor
timestamp: May 25, 2019, 10:25:50 pm
content: If it shows short in both directions, it's bad and should be replaced.

author: 2X
author_rank: Frequent Contributor
timestamp: May 26, 2019, 09:18:57 am
content: The problem is that I didn't know which is the breakdown voltage (if it is zener diode).

author: MagicSmoker
author_rank: Super Contributor
timestamp: May 26, 2019, 12:00:07 pm
content: The color band code for MELF zener diodes is not standardized, but it looks like Z2 has the same band so if it is ok then you can apply a current-limited variable voltage across it to determine the breakdown voltage. Basically, insert a 10k resistor in series with the positive terminal of an external power supply (ideally a variable one) and measure the voltage across Z2 when this current-limited voltage is applied. If you connect positive to cathode then the voltage will clamp at the zener voltage (+/- a few %); if you connect it positive to anode then it will clamp at 0.6-0.7V.(mini rant: this is also an excellent object lesson in why you should never use MELF package parts!)

author: Brumby
author_rank: Unknown
timestamp: May 26, 2019, 02:36:15 pm
content: Quote from: MagicSmoker on May 26, 2019, 12:00:07 pmDave might take exception to that. He is a self-confessed MELF fan boy.

author: Jwillis
author_rank: Super Contributor
timestamp: May 26, 2019, 03:25:07 pm
content: My eyes are very poor so I cant make out the colors but I found this stuff that may help.https://cdn.instructables.com/ORIG/FUD/YCRF/IFSHEG3P/FUDYCRFIFSHEG3P.pdfFound it here which has other stuff that may be helpful in other areashttps://www.instructables.com/id/From-Resistors-to-ICs-Color-Codes/

author: Ysjoelfir
author_rank: Frequent Contributor
timestamp: May 26, 2019, 03:52:11 pm
content: Quote from: Brumby on May 26, 2019, 02:36:15 pmI may have missed it, but what is the problem with MELF? I personally love the package.

author: Brumby
author_rank: Unknown
timestamp: May 26, 2019, 04:02:34 pm
content: Another fan boy!

author: Ysjoelfir
author_rank: Frequent Contributor
timestamp: May 26, 2019, 05:32:17 pm
content: Quote from: Brumby on May 26, 2019, 04:02:34 pmAbsolutely

author: exe
author_rank: Unknown
timestamp: May 26, 2019, 07:19:22 pm
content: I love melf... until I start soldering them.

author: MagicSmoker
author_rank: Super Contributor
timestamp: May 26, 2019, 08:27:21 pm
content: Quote from: Ysjoelfir on May 26, 2019, 03:52:11 pmHuh, I didn't think this would be a controversial opinion, but hey, everyone has their preferences! I personally dislike MELF diodes because I can't reliably pick them up with the vacuum nozzle on my pick-and-place, and it seems the painted cathode mark/color bands come off too easily compared to the laser etching on epoxy body components (e.g. - SOD137, etc.). That said, laser-etched cathode marks aren't exactly easy to see, either.

author: Brumby
author_rank: Unknown
timestamp: May 27, 2019, 12:57:33 am
content: I wouldn't be too concerned with differing opinion. I'd bet money that the MELF fan boys don't use pick and place machines with them.

author: Ysjoelfir
author_rank: Frequent Contributor
timestamp: May 27, 2019, 06:03:32 am
content: Quote from: Brumby on May 27, 2019, 12:57:33 amThat's correct. I populate my prototypes by hand and let someone else do the assembling when something goes into production. Never had complaints about MELF from the assembly house though. Is it really that hard to pick and place those? Sure, they aren't flat, but I thought the nozzles on the PnP machines are soft enough to wrap around a cylindrical component, aren't they?