Help Identifying Component - Page 1
Forum section: electronics / beginners

author: Vhsfi
author_rank: Newbie
timestamp: November 05, 2011, 02:08:00 pm
content: Hi,I would apreciate if someone could tell me what the component that is between the two capacitors is in the attached pic.It's part of a small board where the phone line connects in a fax equipement.Thx for any help

author: Axel1973
author_rank: Regular Contributor
timestamp: November 05, 2011, 06:42:33 pm
content: im not realy able to read the printing on the board, nor where the second lead is going to.some more photos , also showing it from the side with better colors would be helpful.anyhow.. my first guess is "a diode" or "z-diode". since there seems to be a single blue ring around it, that is off the center of the glass tubing. by desoldering it you should be able to test it with a multimeter in diode-test mode or resistance-test mode by testing BOTH directions.

author: Unknown
author_rank: Unknown
timestamp: November 05, 2011, 07:10:16 pm
content: Since one lead appears to be loose, it can be measured as is.

author: Vhsfi
author_rank: Newbie
timestamp: November 05, 2011, 08:10:03 pm
content: Hi,The component marking on the pcb reads MIS1 i already tested it with the multimeter and i get nothing on resistance, diode test, or continuity and the component is good as the board was pulled from a working fax machine, i have another one just like that where that component literaly broke in half due to an electrical discharge from thunder storm, i don't have the board here with me but i think that component is connected to the same tracks of the capacitors, also i have some 56k modems lying around and all have a similar component near the phone line connector but the pcb markings read RV1 and the ring colors on the components are different. Will try to get some more pictures. Thx for the help

author: amspire
author_rank: Super Contributor
timestamp: November 05, 2011, 09:32:55 pm
content: I think it might be a transient suppression diode device - basically two back to back zeners.Operates faster then varistor-type devices.Not used to seeing glass encapsulated ones, bit it might be a low capacitance version for the telecom industry.

author: Axel1973
author_rank: Regular Contributor
timestamp: November 05, 2011, 09:34:37 pm
content: no continuity reading on any direction? hmm..possibly a kind of spark bridge? (high voltage fuse kinda thingy),maybe a DIAC?The German Wikipedia Article on Diacs mentioned that in telephony applications (fax including) its been used to supress strong clicks or voltage peaks on the phoneline. Seehttp://de.wikipedia.org/wiki/DiacI was not able to find that note on the english wikipedia page.http://en.wikipedia.org/wiki/DIACSo with some high ohm serial resistor (100K or so) and a high voltage DC power supply (50-100V or so) you possibly can test it. it then should work like two zener diodes that are connected back-to-back or face2face. the high ohm resistor is to protect the device from blasting through high flowing current at the moment when the think would start to break-through or conduct.----/\/\/\/------||||||----assuming that it is a diac.

author: Zad
author_rank: Super Contributor
timestamp: November 06, 2011, 05:56:46 am
content: It is a surge protection spark gap. Under high voltages (e.g. near-by lightning strikes) the gas in the glass capsule ionises and shorts the terminals.http://www.mmea.com/surge_ab/surge02/dss.htm

author: Vhsfi
author_rank: Newbie
timestamp: November 06, 2011, 12:16:20 pm
content: It seemed to be some kind of surge protection component, just didn't know what it was, mystery solved.Thx everyone for the help.

author: Godzil
author_rank: Frequent Contributor
timestamp: January 14, 2016, 07:26:28 pm
content: Wrong topic, sorry