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How can a 72MHZ receiver crystal go bad?

Old 01-03-2015, 06:56 PM
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golf4two
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Default How can a 72MHZ receiver crystal go bad?

Futaba R127DF receiver on channel 45 has worked fine for many, many years in same airplane. Receiver crystal obtained from Tower years ago. Plane has been flown off and on every few months since built and is stored inside our home. Tried to fly last week but got no response from transmitter. Hmmmm.... Trouble shooting at home by checking batteries, connections, etc. No luck. Swapped in a new receiver on same channel. Works fine. Receiver problem. On a whim, pulled crystal and substituted one from another receiver. Aha, bad receiver now works fine. Put "bad" crystal in known good receiver....doesn't work. To be sure, tried same type swaps with still another receiver...same results. Conclusion is crystal went belly-up. How can that be? Didn't think anything could possibly go wrong with a crystal. (And no, no obvious corrosion or damage to it.) Ideas anyone?
Old 01-03-2015, 07:19 PM
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radfordc
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Probably a broken crystal...like this: http://commons.wikimedia.org/wiki/Fi...oscillator.jpg
Old 01-03-2015, 08:00 PM
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golf4two
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Thanks radfordrc. That's the only thing that makes sense to me. Didn't realize how fragile it might be. Think I'll try to take the case off and see what it actually looks like. Still can't figure what could possible have caused it though.
Old 01-04-2015, 11:23 AM
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Zeeb
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Umm I don't wish to further complicate you issue nor can I swear that the information is accurate. I had one of the Avionics guys at the airport where I worked tell me that crystals can also get off tune. That is the major reason that the FCC won't let anyone work on a radio transmitting device without a certification and the ability to check the frequencies and in the case of a tx, it's power output.
Old 01-04-2015, 11:59 AM
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Truckracer
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Yes, they can get out of tolerance (off frequency) and they can lose activity meaning they may resist starting to oscillate when first turned on. Other than fracture as shown in the link above, they can also get chipped on the edge from ground impact which can render them off frequency, etc. though they can still seem to work normally. Simple range tests can show serious defects.

I don't miss crystals!
Old 01-04-2015, 02:09 PM
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golf4two
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Got out the old Dremmel and did some microsurgery. Best pic I could get with my cell phone, Whatever and however it happened, they are cheap enough. Thankfully it didn't happen while in the air. Transitioning a dozen or so airplanes to 2.4 is gonna hurt the old pocketbook! Better safe(er) than sorry though. Thanks for the insight guys....once again I learned something so the day was not a total loss.

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Old 01-05-2015, 09:07 PM
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sidgates
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Crystals are the most fragile component in an R/C receiver. Vibration and sudden stops are very hard on them. Also as others have stated they can drift with age. The higher the frequency of the receiver the thinner the crystal element and the easier to damage. When I had a service shop for receivers we always checked the receiver for vibration using a hand vibrator. There was a fine line between enough vibration to check the crystal and too much that would damage it.
Old 01-06-2015, 01:32 AM
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Tommy91
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my rc tank crystals also gone bad within one month of purchase.
Old 01-10-2015, 02:08 PM
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aeajr
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Typically vibration or crashes will do in a crystal.

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