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Car remote Keyfob.

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RMIM

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I opened up my car remote keyfob (it’s for a car alarm that has remote start and 2 way pager) as the battery terminal was a bit dodgy – then 2 my horror a component dropped out. I loved that system (a mannix sm700). It still seems to come on, not sure if it actually still works as I took the car alarm out of my old car and had plans to fit it in my new car.

Anyway – the component that fell out looks like a watch crystal

**broken link removed**

but has 20.9 COY stamped on the can.

What is it? Where can I get a new one?

It will be hard to solder the old one back on as the legs have broken, leaving nothing to work with.

Thanks
 
The device is probably a 20.9 MHz cylindrical crystal used in the transmitter frequency control circuit. Here on this side of the pond, one supplier is Bomar Crystal -- I know that you won't be able to purchase just one, but perhaps a "sample" might be available??
 
Thanks for the reply ChrisP - a crystal sounds like an easy/cheap enough thing to buy - trouble is I can’t seem to find 20.9Mhz! Why would the UK not stock it? Can I use a similar fq without having to alter something in the receiver? Maybe I will try ebay in the US.
 
Thanks for the reply ChrisP - a crystal sounds like an easy/cheap enough thing to buy - trouble is I can’t seem to find 20.9Mhz! Why would the UK not stock it? Can I use a similar fq without having to alter something in the receiver? Maybe I will try ebay in the US.

It's a special crystal for a special purpose - you MUST use the correct frequency, or the fob won't work.
 
thanks for the reply.

Where to get one though?

No idea, special crystals are difficult to find - usually you would buy them from the manufacturer of the item you're trying to repair, or from the source of the chip that requires it. Prersumably neither are available to you, or even known?.
 
No idea, special crystals are difficult to find - usually you would buy them from the manufacturer of the item you're trying to repair, or from the source of the chip that requires it. Prersumably neither are available to you, or even known?.



I see, I had no idea it worked like that – I thought all these types of component were readily available. Oh well looks like I have to buy a whole new alarm. (They don’t seem to sell this model of alarm anymore, so I can’t buy a new fob.)

I suppose I could try to perform some type of surgery on the component – but the amount of metal showing are like pin pricks.
 
It might be possible - I'd start by mechanically fixing the old crystal (glue), then putting solder balls onto the legs, connecting to little offcuts of resistor-lead connecting the crystal to the board.

It should be possible (I hope) if there is a little bit of leg left.

Andrew
 
I see, I had no idea it worked like that – I thought all these types of component were readily available. Oh well looks like I have to buy a whole new alarm. (They don’t seem to sell this model of alarm anymore, so I can’t buy a new fob.)

A couple of points...

1. As Nigel said, if you replace the crystal, the replacement must be an exact match if you want the fob to "talk" to the alarm system successfully. The reason for this is because the crystal is the means of "setting" the frequency of the transmitter in the fob. These devices are usually locked in at a given comm freq with no tuning adjustment capability provided in the circuit. The actual transmitter freq is usually marked on the fob. Here in the states, such marking is required by our Federal Communications Commission (FCC). Further, these devices are usually licensed for operation at specific freqs, with pretty rigid attenuation required either side of the assigned freq.

2. Here in the states, almost any remote fob is available "à la carte" at most better auto parts jobbers. Take the fob to your local parts jobber and see if they don't have a replacement listed. Note that it most likely will not be listed per application - rather, they should be able to cross reference the fob manufacturer's model/part number. Lacking that, many remotes can be identified (i.e., matched) simply by freq and function(s)...

Good luck - and let us know how you make out with this - whichever course you end up following... :)
 
Keyless Remote FOBs

If you didn't already find one, check out this site, they are quick. I got mine there.
:eek:
 
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