Surface mount diode identification

:I have an alarm board with two shorted surface mount diodes. These are :about the size of a quarter watt carbon resistor only just a slight :bit fatter. They are marked: MX6AA and MX50AA. Can anyone please :identify these for me? Thanks, Lenny.

Are they glass MELF style or moulded plastic similar to either of these photos?

My first guess would be 1W zeners so perhaps you can check to see if they have

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They are not round more like flat and they are definitly shorted. Lenny

:On Aug 30, 3:28 am, Ross Herbert wrote: :> On Sat, 29 Aug 2009 11:53:54 -0700 (PDT), " snipped-for-privacy@yahoo.com" :>

:> wrote: :>

:> :I have an alarm board with two shorted surface mount diodes. These are :> :about the size of a quarter watt carbon resistor only just a slight :> :bit fatter. They are marked: MX6AA and MX50AA. Can anyone please :> :identify these for me? Thanks, Lenny. :>

:> Are they glass MELF style or moulded plastic similar to either of these photos?

:> My first guess would be 1W zeners so perhaps you can check to see if they have :> 6V and 50V ratings respectively (assuming they are not dead). :They are not round more like flat and they are definitly shorted. :Lenny

'Fraid you are stuffed then.. Other than figuring out the function by tracing out the circuit around those devices and then making some intelligent deductions...

No manufacturer ident (on the board or the system) you can approach?

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The board is a fire alarm main board and is manufactured by GE Security probably off shore. These diodes could be anyones I guess. The thing is, this exact failure, that is these two diodes shorting out has happened many times before on this security installation. It usually occurrs after a bad lightning storm. For the time being GE has repaired these units under warranty but the warranty period is coming to an end. These boards are no longer in production so it also involves sending the board out for repair and so the premises are not protected during that period. I would have to guess that at least one of these diodes is accross the input reversed biased to ground because when it shorts out the unit displays "Ground fault" and the zone is knocked out of commission. Would you think that this is probably a zener or perhaps just a standard run of the mill diode? Lenny

Lenny, you should check the liability of repairing fire alarm hardware without the OEM's blessings. You may end up assuming all liability if something goes wrong. If the laws haven't been changed, any repair other than replacing a failed board with anything other than a factory built or repaired assembly makes you liable for future losses. When I investigated this years ago I was told that I needed the original OEM service data, and a minimum of 10 million dollars in liability insurance. I'm sure it has gone up, over the years.

I know it seems theres always a lawyer where ever you look these days.Lenny

On Wed, 2 Sep 2009 23:21:30 -0700 (PDT), snipped-for-privacy@yahoo.com put finger to keyboard and composed:

photos?

Could they be transient voltage suppression (TVS) diodes? Transorbs? Mosorbs?

- Franc Zabkar

:On Sep 2, 5:19 am, Ross Herbert wrote: :> On Mon, 31 Aug 2009 05:18:42 -0700 (PDT), snipped-for-privacy@yahoo.com wrote: :>

:> :On Aug 30, 3:28 am, Ross Herbert wrote: :> :> On Sat, 29 Aug 2009 11:53:54 -0700 (PDT), " snipped-for-privacy@yahoo.com" :> :>:> wrote: :>

:> :>

:> :> :I have an alarm board with two shorted surface mount diodes. These are :> :> :about the size of a quarter watt carbon resistor only just a slight :> :> :bit fatter. They are marked: MX6AA and MX50AA. Can anyone please :> :> :identify these for me? Thanks, Lenny. :> :>

:> :> Are they glass MELF style or moulded plastic similar to either of these :>

photos?

:> :> My first guess would be 1W zeners so perhaps you can check to see if they :> have :> :> 6V and 50V ratings respectively (assuming they are not dead). :> :They are not round more like flat and they are definitly shorted. :> :Lenny :>

:> 'Fraid you are stuffed then.. Other than figuring out the function by tracing :> out the circuit around those devices and then making some intelligent :> deductions... :>

:> No manufacturer ident (on the board or the system) you can approach? : :The board is a fire alarm main board and is manufactured by GE :Security probably off shore. These diodes could be anyones I guess. :The thing is, this exact failure, that is these two diodes shorting :out has happened many times before on this security installation. It :usually occurrs after a bad lightning storm. For the time being GE has :repaired these units under warranty but the warranty period is coming :to an end. These boards are no longer in production so it also :involves sending the board out for repair and so the premises are not :protected during that period. I would have to guess that at least one :of these diodes is accross the input reversed biased to ground because :when it shorts out the unit displays "Ground fault" and the zone is :knocked out of commission. Would you think that this is probably a :zener or perhaps just a standard run of the mill diode? Lenny

I doubt it is a standard diode. More like a zener or transorb. Did you try the GESecurity website? I notice that if you have a login and password you can get access to the reference manual for some of their FA systems, eg. Fireworx;

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I talked to the area rep. No they won't tell me anything. "company secrets" or some other bullshit. The only thing to do is have them repair the board and then remove the new parts and try to put them on a curve tracer perhaps. Lenny.