Identify Components by SMD code - Page 1
Forum section: electronics / repair

author: Wilksey
author_rank: Super Contributor
timestamp: January 13, 2022, 06:08:06 pm
content: Hi,Can anybody help identify the 2 components in the picture?One has what looks to be 731 B34 and looks like the On Semi logo, the other looks like is has 73 4A, I am presuming these are diodes as they go across the VCC + GND points.I think the large one is a zener of some kind and the smaller one is a TVS perhaps, the power comes in (3V3 or 5V) goes to a fuse, then passes by these and then connects to a E2PROM chip, standard 8KByte Microchip 25LC641.Cheers

author: fzabkar
author_rank: Super Contributor
timestamp: January 13, 2022, 06:20:11 pm
content: "B34" could be a Schottky rectifier:https://www.onsemi.com/pdf/datasheet/mbrs340t3-d.pdfhttp://www.smdmark.com/en-US/search/code?id=B34I expect that "4A" would be a 5V TVS diode.The former would provide reverse polarity protection while the latter would handle overvoltages.

author: gamalot
author_rank: Super Contributor
timestamp: January 13, 2022, 07:10:56 pm
content: The one in the SMA package should be a 5.6V Zener diode 1SMA4734A.https://html.alldatasheet.net/html-marking/1296757/LEIDITECH/1SMA4734A/1143/2/1SMA4734A.html

author: fzabkar
author_rank: Super Contributor
timestamp: January 13, 2022, 11:11:21 pm
content: Quote from: gamalot on January 13, 2022, 07:10:56 pmI think that "73" may be a date code.This is what a 1SMA4738A looks like:https://www.taobao.com/list/item/599114971429.htm?spm=a21wu.10013406.taglist-content.4.673b990byuSgrY

author: whatboy
author_rank: Regular Contributor
timestamp: January 14, 2022, 12:41:01 am
content: https://www.s-manuals.com/smd

author: Wilksey
author_rank: Super Contributor
timestamp: January 14, 2022, 02:18:09 am
content: Thanks for all of your replies,I looked at a SMD code table but it didn't make sense for "4A" to be a 2V zener, but I did find another reference to a TVS with 4A markings.The larger one could well be a schottky diode, I don't get continuity through either of the diodes in either direction, which made the think it is not a simple diode.I have since discovered that VCC also goes into a TVS diode as part of a chip like this:https://www.diodes.com/assets/Datasheets/ds31271.pdfWould there be 2 TVS diodes on the VCC line?I have seen a picture of another similar circuit which has a large black diode and that part number actually shows it as a 5.6V 3W zener, but I can't see one with B34 markings.

author: fzabkar
author_rank: Super Contributor
timestamp: January 14, 2022, 03:27:06 am
content: There are plenty of "B34" images here:https://www.google.com/search?q=mbrs340t3&tbm=isch&tbs=itp:photo

author: Wilksey
author_rank: Super Contributor
timestamp: January 14, 2022, 11:56:45 am
content: Yes, the more I look at it the more I am convinced you are right with the Schottky barrier diode,So do you think the smaller one "4A" is more likely to be a TVS or a zener?

author: gamalot
author_rank: Super Contributor
timestamp: January 14, 2022, 12:00:51 pm
content: Quote from: fzabkar on January 13, 2022, 11:11:21 pmZener diodes with this part number can come from many different manufacturers, and they don't necessarily have the same marking layout.