Check your parts boxes - crystal needed

[N8YX]

A counter I recently bought has a faulty timebase oscillator crystal - HC18, 12.800MHz.

Anyone have a spare? The OE part was made by Tyco Electronics, and while a number of "obsolete" parts houses list them in stock I doubt they'll deal with an individual.

[kf0rt]

Nothing here -- assume you've checked Mouser, et al.

Do the obsolete thing, and you can be the kingpin of HC18 parts. Ugh.

[KC2UGV]

Nothing here... I swore I pulled a 12.8 from a mobo a few weeks back :(

[K7SGJ]

Can you adapt a SMT xtal? If so, Digikey has some for a couple of bucks.

[KG4CGC]

Can you adapt a SMT xtal? If so, Digikey has some for a couple of bucks.

Would that require a case cover of some sort? I don't even know ... what an SMT crystal would look like.

[NA4BH]

For those that are completely stupid (ME) as to what you are talking about, could you post a picture? I have a bunch of old crap around here. Would this crystal only be in a radio?

[KA9MOT]

12.900? Will it work?

[N8YX]

For those that are completely stupid (ME) as to what you are talking about, could you post a picture? I have a bunch of old crap around here. Would this crystal only be in a radio?
Here's a size reference:

5445

The -18 can either have wire leads or pins.


Can you adapt a SMT xtal? If so, Digikey has some for a couple of bucks.

I noticed the Digikey and Mouser carry devices of the required frequency, but the load capacitance (10pF series) is wrong. Needs to be on the order of 25-32pF parallel.


12.900? Will it work?

Unfortunately, no. The 12.800MHz oscillator is divided down by a series of 7493 counters to get a 2.5Hz gating frequency; if the gating window is longer or shorter than this by even a small amount then the counter isn't accurate. The trimmer circuit as designed won't allow a 12.900MHz rock to be pulled enough to work.

[K7SGJ]

Here's a size reference:

5445

The -18 can either have wire leads or pins.



I noticed the Digikey and Mouser carry devices of the required frequency, but the load capacitance (10pF series) is wrong. Needs to be on the order of 25-32pF parallel.



Unfortunately, no. The 12.800MHz oscillator is divided down by a series of 7493 counters to get a 2.5Hz gating frequency; if the gating window is longer or shorter than this by even a small amount then the counter isn't accurate. The trimmer circuit as designed won't allow a 12.900MHz rock to be pulled enough to work.

How about an osmod? The outputs are are typically high enough that loading won't be a issue, and depending on what you get, all you need is 3v, 5v, or 12v. Accuracy is quite high so the trimmers won't be necessary, wouldn't affect the frequency anyway. I don't think the clipped sine would be an issue, either. They only cost a couple of bucks and would be worth a try until you can find a rock that will work, or have to order one from ICM or Jan. You can get pure sine units, but they are higher than giraffe nuts. I'll keep looking around. I'm sure we can find something cheap or broken somewhere that uses them.

http://search.digikey.com/us/en/products/FOX914B-12.800/631-1062-2-ND/1024654

[N8YX]

I'll keep looking around. I'm sure we can find something cheap or broken somewhere that uses them.

Just checked those modules out - might work if the accuracy was 2ppm or less.

As far as the crystal application itself, the frequency was common to PLL circuits in Tram and CPI CBs, CPI accessories (an FC-70 is the counter in question) and I'm not sure what else.

I managed to snag two used rocks off eBay last night which will hopefully be operative but I'm still on the hunt for a new one.

[W9JAM]

not sure if this helps but.... http://www.af4k.com/hc50u_crystals.htm

[N8YX]

not sure if this helps but.... http://www.af4k.com/hc50u_crystals.htm
Saw that the other night, Jeremiah. If the two eBay rocks don't work I may drop this guy a line...but his prices are a tad steep.

[N8YX]

Two eBay crystals showed up today.

Picked one at random, soldered into counter and changed a couple other questionable parts while I had the iron hot...

Bingo! Operation has been restored.

Threw the counter inline with a transceiver and netted the trimmer cap as the unit read the transceiver's frequency. A break for dinner then buttoned up the case and it's done. Thanks for everyone's suggestions and junk-box inspections - luckily, I was able to get this thing back into working order cheap.

[KA9MOT]

Sweet success! Nice work!