Help Identifying SM Diode - Page 1
Forum section: electronics / general

author: SgtRock
author_rank: Unknown
timestamp: December 13, 2012, 08:34:53 pm
content: Greetings EEVBees:--Please help me in my ignorance. My Acer S231HL LCD LED refurbished monitor from Geeks.com was dead this morning. The power light was off and it seemed slightly warm in the 19V PS plug area. No complaints, it worked for over a year and was very cheap. My problem is in identifying Diode # 701 on the board that the PS plugs into, see pictures. Below are results of diode and resistance test with my Fluke 87V.--Diode 701 fails diode test and shows 0 V both directions. It also shows 0.35 Ohms both directions.--Diode 703, which is marked the same passes diode test with 1.51V in one direction and 0.155V in the other direction. Resistance is infinite in the one direction and 150 Ohms in the other.--I am assuming the Diode 703 is alright and that Diode 701 is kaput.--Both Diodes are marked S21F with SM340A directly underneath.--I would appreciate it if any one could tell me just what Diode 701 is and where to get a replacement."He was born ignorant, and has been losing ground ever since."Fred Allen 1894 - 1956Best RegardsClear Ether

author: tom66
author_rank: Super Contributor
timestamp: December 13, 2012, 08:43:19 pm
content: 3A, 40V diodes in what looks to be maybe an SMB or SMA case.

author: free_electron
author_rank: Super Contributor
timestamp: December 13, 2012, 08:56:45 pm
content: standard diode available under many names. like on semiconductorMBRS340,MURS340,B340, and many other names depending on manufacturer.This is one of these components like a 7400. SN7400 is texas .CD7400 is RCa DM7400 is national F7400 is fairchild and so on ...3 ampere , 40 volt standoff voltage.

author: SgtRock
author_rank: Unknown
timestamp: December 13, 2012, 09:04:02 pm
content: Dear Tom66 and FreeElectron:--Once again thank you all for the knowledgeable and timely advice. Between the two of you, you have nailed its hide to the barn door. Now that I know I can source the little bugger I will continue to test some of the other devices on the board. I will report back later. There was a 470µF 10V Cap on the board that was showing 0.00 flickering to 0.01 ESR. I broke a pin trying to desolder it, so we will never know if it was really bad, but I assume so. Like Dave I have not yet acquired any good Vacuum Desoldering Equipment, and it is getting to be a priority item as I desolder stuff on more and more expensive and irreplaceable boards. I plan on getting used Hakko Desoldering Station equipment. Any advice on that topic would be appreciated. Thanks again, very much."I'll have the Alfalfa sandwich, and the smashed yeast"Woody Allen 1935 -Best RegardsClear Ether

author: SgtRock
author_rank: Unknown
timestamp: December 16, 2012, 03:17:18 am
content: Greetings EEVBees:--Zener Diode 702, see picture, is blown. Fails diode test with zero ohms both ways. It is connected to the negative side of a 220µF 25V Electrolytic Capacitor. It is as SM glass copper zener with a white band covering about 2/3s of the body. Could anybody please tell me what to replace it with or how to go about identifying it."Does not squirrel crack nuts on bough of oak tree."Lao Fu 1410 1620Best RegardsClear Ether