Post by thread:[EE] Dead Mystery Component

Hi: A computer monitor stopped working and had that smell. After getting it apart enough to have a look found this circular component cracked almost into two parts and the PCB is charred on one leg. It's at the line input section of the mains power supply right next to a bridge rectifier and large filter cap. On the pcb below the part is what looks like a schematic symbol in the form of a "Z". Photo at: http://www.prc68.com/I/HaT.shtml#CM What is it? Do they fail, or is it likely something down stream is shorted? -- Have Fun, Brooke Clarke http://www.prc68.com/Alpha.shtml All my web pages listed based on html name http://www.PRC68.com http://www.precisionclock.com http://www.prc68.com/I/WebCam2.shtml 24/7 Sky-Weather-Astronomy Web Cam

Brooke Clarke wrote: > Hi: > > A computer monitor stopped working and had that smell. After getting it apart > enough to have a look found this circular component cracked almost into two > parts and the PCB is charred on one leg. It's at the line input section of the > mains power supply right next to a bridge rectifier and large filter cap. On > the pcb below the part is what looks like a schematic symbol in the form of a > "Z". Photo at: http://www.prc68.com/I/HaT.shtml#CM > > What is it? Do they fail, or is it likely something down stream is shorted? > > I suspect it is a surge supressor.

Usually called a surgistor. -----Original Message----- From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@spam@mit.edu] On Behalf Of peter green Sent: Tuesday, January 22, 2008 1:10 PM To: Microcontroller discussion list - Public. Subject: Re: [EE] Dead Mystery Component Brooke Clarke wrote: > Hi: > > A computer monitor stopped working and had that smell. After getting > it apart enough to have a look found this circular component cracked > almost into two parts and the PCB is charred on one leg. It's at the > line input section of the mains power supply right next to a bridge > rectifier and large filter cap. On the pcb below the part is what looks like a schematic symbol in the form of a > "Z". Photo at: http://www.prc68.com/I/HaT.shtml#CM > > What is it? Do they fail, or is it likely something down stream is shorted? > > I suspect it is a surge supressor.

I believe it is a transorb or MOV. Either way, it is a surge supressor. It is likely just after the input fuse and in parallel accross the AC input. Sometimes after repeated surges they permanently short. Most likely you don't have a problem down the line that caused the problem. Brian Kraut Engineering Alternatives, Inc. http://www.engalt.com {Original Message removed}

Lollipop? It looks like a surge protector to me. I forget the real name for them. Brooke Clarke wrote: {Quote hidden}> Hi: > > A computer monitor stopped working and had that smell. After getting it apart > enough to have a look found this circular component cracked almost into two > parts and the PCB is charred on one leg. It's at the line input section of the > mains power supply right next to a bridge rectifier and large filter cap. On > the pcb below the part is what looks like a schematic symbol in the form of a > "Z". Photo at: http://www.prc68.com/I/HaT.shtml#CM > > What is it? Do they fail, or is it likely something down stream is shorted? >

Hi, It looks lika a varistor. See: <http://en.wikipedia.org/wiki/Varistor> They are supposed to take the heat if there is a short transient on the line voltage. BUT - Its clamping voltage gets degraded by each transient. Too many transients and you may get this result. It could also be that the transient surge is too long or has too much energy for the varistor to handle. It should not be damaged by failed components down stream in the circuit. /Ruben {Quote hidden}> Hi: > > A computer monitor stopped working and had that smell. After getting it apart > enough to have a look found this circular component cracked almost into two > parts and the PCB is charred on one leg. It's at the line input section of > the > mains power supply right next to a bridge rectifier and large filter cap. On > the pcb below the part is what looks like a schematic symbol in the form of a > "Z". Photo at: http://www.prc68.com/I/HaT.shtml#CM > > What is it? Do they fail, or is it likely something down stream is shorted? > > -- > Have Fun, > > Brooke Clarke ============================== Ruben Jönsson AB Liros Electronic Box 9124, 200 39 Malmö, Sweden TEL INT +46 40142078 FAX INT +46 40947388 rubenKILLspampp.sbbs.se ==============================

Quoting Brooke Clarke <.....brookeKILLspam.....pacific.net>: > Hi: > > A computer monitor stopped working and had that smell. After > getting it apart > enough to have a look found this circular component cracked almost into two > parts and the PCB is charred on one leg. It's at the line input > section of the > mains power supply right next to a bridge rectifier and large filter cap. On > the pcb below the part is what looks like a schematic symbol in the form of a > "Z". Photo at: http://www.prc68.com/I/HaT.shtml#CM > > What is it? Do they fail, or is it likely something down stream is shorted? Almost 100% it is a Metal Oxide Varistor (MOV). They typically fail shorted, and likely nothing else is bad behind it. You can replace it with another of the same physical diameter and with appropriate voltage rating. Digikey and others carry these parts, even Radio Shack used to have some. Best regards, Spehro Pefhany -- "it's the network..." "The Journey is the reward" EraseMEs...spam_OUTTakeThisOuTinterlog.com Info for manufacturers: http://www.trexon.com Embedded software/hardware/analog Info for designers: http://www.speff.com

Hi there, Brooke. Couple of possibilities: its either a surge suppressor (MOV) **or** its a NTC surge-limiting thermistor. How do you tell? If its a MOV, it will be across the line. If its a surge-limit thermistor, it will be in series with the line. One additional clue: NTC surge-limiting thermistors often have a rubber coating to act as a thermal barrier. The idea is that they are initially high resistance, thus limiting the peak current into the filter caps. As they get hot, the resistance drops. But, because the resistance drops, they want to cool down. Having an insulating coating allows them to remain hot and thus have a lower ON resistance. They used to be common in TV sets and I've also seen them in older switch-mode power supplies. dwayne At 11:56 AM 1/22/2008, Brooke Clarke wrote: {Quote hidden}>Hi: > >A computer monitor stopped working and had that smell. After >getting it apart >enough to have a look found this circular component cracked almost into two >parts and the PCB is charred on one leg. It's at the line input >section of the >mains power supply right next to a bridge rectifier and large filter cap. On >the pcb below the part is what looks like a schematic symbol in the form of a >"Z". Photo at: http://www.prc68.com/I/HaT.shtml#CM > >What is it? Do they fail, or is it likely something down stream is shorted? -- Dwayne Reid <dwaynerspam_OUTplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax http://www.trinity-electronics.com Custom Electronics Design and Manufacturing

Charles Craft wrote: > I've seen them with a notched package. > Is this done by the MOV manufacturer or the device manufacturer? > I assume it's to let the magic smoke out when they go shorted? > On some ceramic disc through hole capacitors, this is done as a spark-gap. These are (or were) often used in the H.V. section of television sets.