BIG PROBLEM WITH RECIVER OR TRANSMITTER
01-12-2003, 02:41 PM
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BIG PROBLEM WITH RECIVER OR TRANSMITTER
I took this radio equip from a cox airplane. The controller is a cobra. The reciver is also cox it works on 72mhz am 2 channel radio reciver. The servo is also cox and the # it saids is 80111. I took this out of the airplane that crashed but not a hard crash about 2 years ago. A year ago i tried it for the hell of it and it worked. Not a year later it dosen't work. What happens is when i connect everything only one servo works and it only works if i connect the reciver wire directly to the controller and even like that it really on flickers the servo a little. Is their a way to test the radio equip. or the broken servo???
01-12-2003, 07:19 PM
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BIG PROBLEM WITH RECIVER OR TRANSMITTER
Reapairing equipment such as this is usualy more expensive than its worth... The cheap 2 ch setups just don't have enough value.
The desctiption sounds like the crystal in the RX went bad. If it was craked in the crash, and then went through a few cycles of temperature rising and falling durring storage, the crystal coud have virtually disintigrated inisde its little metal can. When the crystal goes away... the RX is detuned and may not be able to sense the TX at all.
A cheap crystal is at least $8. If you can get one for that radio... (other crystals specified for the same frequency probably will not work... some are cut at 1/2 frequency, some at 1/3, some at 1/4... then the RX circuitry multiplies the oscillation rate.)
If the crystal is all thats wrong, it may be worth the cost... But if that doesn't fix it, then you've got that much spent, and still have a broken old radio.
The desctiption sounds like the crystal in the RX went bad. If it was craked in the crash, and then went through a few cycles of temperature rising and falling durring storage, the crystal coud have virtually disintigrated inisde its little metal can. When the crystal goes away... the RX is detuned and may not be able to sense the TX at all.
A cheap crystal is at least $8. If you can get one for that radio... (other crystals specified for the same frequency probably will not work... some are cut at 1/2 frequency, some at 1/3, some at 1/4... then the RX circuitry multiplies the oscillation rate.)
If the crystal is all thats wrong, it may be worth the cost... But if that doesn't fix it, then you've got that much spent, and still have a broken old radio.
01-13-2003, 10:27 PM
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BIG PROBLEM WITH RECIVER OR TRANSMITTER
Thanx for the information but i have another question if i put a crystal chip from another rc car will that work
01-13-2003, 10:51 PM
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BIG PROBLEM WITH RECIVER OR TRANSMITTER
72 mhz systems in the US are for AIRCRAFT ONLY.
The crystal from a car radio will be on a different frequency band. The RF deck of the RX can not tune to that far different of a crystal without being sent in to a shop (and then... its expensive if possible at all... possibly needing replacment of several components.)
The same goes for the transmitter. You can't just plug in a crystal and hope. (in fact... its illegal to play "musical crystals" in the transmitter.)
Because of people playing with changing transmitter crystals... there is a possibility that the FCC will require manufacturers to "pot" the RF deck, encasing the crystal and some other components in a non-conductive epoxy. This would make repairs of the transmitter RF decks impossible. If you don't want this to happen... spread the word that changing crystals is inappropriate.
A transmitter NEEDS to be fine tuned to match the replacement crystal, even if its the same frequency. If the original crystal was off the max limit high and the replacement is off max limit low... the transmitter could be off frequency enough that it can't even communicate with a properly tuned natrrow band reciever.
You CAN find someone with a matching radio system, trade reciever crystals and test using his transmitter... THAT would work, as long as it is in the same frequency band.
The crystal from a car radio will be on a different frequency band. The RF deck of the RX can not tune to that far different of a crystal without being sent in to a shop (and then... its expensive if possible at all... possibly needing replacment of several components.)
The same goes for the transmitter. You can't just plug in a crystal and hope. (in fact... its illegal to play "musical crystals" in the transmitter.)
Because of people playing with changing transmitter crystals... there is a possibility that the FCC will require manufacturers to "pot" the RF deck, encasing the crystal and some other components in a non-conductive epoxy. This would make repairs of the transmitter RF decks impossible. If you don't want this to happen... spread the word that changing crystals is inappropriate.
A transmitter NEEDS to be fine tuned to match the replacement crystal, even if its the same frequency. If the original crystal was off the max limit high and the replacement is off max limit low... the transmitter could be off frequency enough that it can't even communicate with a properly tuned natrrow band reciever.
You CAN find someone with a matching radio system, trade reciever crystals and test using his transmitter... THAT would work, as long as it is in the same frequency band.
