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Old Aug 03, 2013, 02:21 PM
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Joined Aug 2013
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Crystal change RC boat

Complete newbie here folks, here's the situation,

Recently went to Turkey, and whilst in a town bought my son an RC boat in a toy shop. Now having returned home to England, we discovered it does not work. Returning it is obviously not an option, and don't really want to chuck 40 down the drain.

Having examined it, I have found the handset has a sticker of 49MHz on it and the sticker on the inside of the boat has 27MHz on it. Now when I touch the antenna on the metal of the propellers and move the control it works, so it seems to be they have mismatched crystals, stopping the radio control working.

I have now taken the handset apart and found the 49MHz crystal, and after taking the board on the boat apart I cannot identify the crystal on the board, does anyone recognise any of these that would be the crystal? I am planning to buy a new pair of crystals and re solder them on to the existing crystals positions, providing I can identify the boat crystal.

Picture of the boat board:



Thanks for any help guys
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Old Aug 03, 2013, 06:25 PM
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EloyM's Avatar
SantaAna CA
Joined Aug 2003
316 Posts
Nothing looks like any crystal used in RC equipment.
However, you can not replace a 27 MHz crystal with one on 49 MHz in either a transmitter or receiver. They are designed for a certain band and sometimes will accept a crystal in the same band. Sometimes though, they require retuning to work properly.
Also crystal for one brand of equipment will seldom work in equipment of another brand
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Old Aug 03, 2013, 11:01 PM
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United States, FL, Wildwood
Joined Jul 2005
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The reason you can't find the crystal is because there isn't one. The older radios have crystals in them, but the newer ones use an integrated chip with a phase lock loop oscillator. That big IC chip is the oscillator and has a tunable coil external. If the tx and rx frequencies are not matched, the radio system will not work. What you have is an inexpensive, "toy" rc. Those radios are completely proprietary and cannot be changed. I would recommend chucking the radio system and upgrading to hobby class equipment. The only other option is to find a transmitter that is on the matching frequency of the receiver.
In your case, you will need to find a transmitter that is designed to work on 27MHZ. It appears that whoever sold this to you, mismatched the boat and transmitter. 27MHZ transmitters are still fairly common and inexpensive, however, you need to get the exact frequency of the receiver. There are many differing frequencies that are used in the 27MHZ band. I know this sounds confusing, but that is the reason the "toy" class rc's are under $100.00. You get what you pay for! If you like the style of the boat, you might be better off getting some hobby grade radio set used perhaps from e-bay. I hope this helps.
Good luck!
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Old Aug 04, 2013, 05:14 AM
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Blackpool, Lancs
Joined Feb 2006
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The 49MHz band is "legal for toys" but has never been used for model control. The real olde way of tuning involved a tuned inductance/capacitance circuit not involving a crystal, the modern equivalent being the phase locked loop. It is likely that the system, rather than precision tuning, just works on a combination of dumb luck and more of the same, without conforming to any known standard.
A check of the board in the boat will probably show a combined radio and control. This means that unless you can find a transmitter of the exact same type but in the right band, the entire system will need changing since it will be using its own protocols and nothing available on the market will match. The upside of upgrading is that it will be controllable.
It might be possible to find someone with the required knowhow and test gear to retune one end or the other to the right band, preferably the RX end, because that would leave you operating in the "approved" 49MHz band, and you would not find your signal being swamped by other users on 27 or 40 MHz.
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Old Aug 04, 2013, 08:48 AM
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Thanks for the help guys, spent a fair few hours googling last night and realised about the chip instead of the crystal on the receiver. I also found the boat is a davy jones spray boat and that there are two colours the white model which runs on 49mhz and the blue model (my sons) which runs on 27mhz. I gather that in the shop at some point the controls have got mixed up since there were white models on the shelves next to the blue.

I know that the 27MHz frequency has 6 channels, since the crystals are available in 6 bands of the frequency, and I've found someone who sells the 6 different channels of 27MHz in a set, so i'm gonna go ahead and buy them and solder each onto the board, and one of them should be picked up by the receiver chip.

Thanks for input anyway fellas, appreciated :-)
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Old Aug 04, 2013, 08:02 PM
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Toronto, Canada
Joined Nov 2004
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Most of the toys offered with dual bands for control do not use individual channels, but use the whole band. Individual frequency crystals will usualy not work with them and at the price of crystal sets you would be better to buy a proper hobby RC set.
Regards,
Gerald..
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Old Aug 05, 2013, 05:13 AM
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Blackpool, Lancs
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Conventional model control systems with a crystal each use a narrow band (or channel) within that main band. The control signal comprises of a series of pulses to give, in turn, each information channel to that particular receiver, or anything else on the same channel. The toys, on the other hand, to ensure low costs, do not. To transmit, they are broadly tuned to somewhere in the stated band and send a weak signal. To receive, they pick up anything that is going on in roughly their band. The signals do not correspond to any generally used standard.
If you can get the RX to accept the 49MHz signals, that will leave you with a working boat. If you mod the TX to use 27MHz, you will have an illegal outfit unless you can get it calibrated and certified. The setting of the core in the coil (top left in your picture) combined with one or more of the capacitors near it will be the local oscillator that the PLL uses as a reference. The capacitor(s) in conjunction with other components in that bit of circuit will set the general band - the coil will act as a fine tune. Whether its the same coil on both 27 and 49 - who knows?
If you really must swap crystals around, have a look for a crystal socket with the right pin spacing. Crystals are not generally amenable to soldering - one of the things that they really don't like is excess temperature, like heat coming up the leg from a soldering operation.
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Old Aug 06, 2013, 10:17 AM
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Ok thanks people. Think I'm going to forget it, just a bit cheesed off it was a waste of money that I thought I might be able to fix by getting the boat to pick up a 27mhz signal from the transmitter.

Not to worry, such is life
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Old Aug 09, 2013, 06:18 AM
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I have found with these cheap R/c toys i always plan on purchasing 2 of them. One to use and another for spare parts. Then you also have 2 sets of parts also to test to see what is wrong.
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Old Aug 11, 2013, 08:00 AM
RC boat Rock Star
Kalamazoo, MI
Joined Apr 2004
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Remember CB radios? They worked in the very same 27 Mhz band.The older ones has crystals inside and some were placing the RC X-tal's inside them and talking on those frequencies, calling them the "funny" channels. We as RCer's only used the 6 legal channels assigned to us. Getting close enough to a CBer at the lake, especially with one who was using an amplifier could make you lose control over your boat as they could bleed over onto other channels.
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Old Aug 14, 2013, 07:51 PM
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bgnome's Avatar
Richmond Virginia
Joined Oct 2009
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Just for giggles, here is a as example of schematic usuage of the RX-2b and TX-2b IC chips. and glancing at the OP's picture of the RX of his model seems to be pretty simular to what is offerd up in the GP schematic.

link to rx/tx-2b chips scematics
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Old Aug 14, 2013, 07:57 PM
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bgnome's Avatar
Richmond Virginia
Joined Oct 2009
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for the external link adverse and for general topic fumbling.. here are the scematics directly..

this is the Transmitter..



this is the receiver:

.

here is the direct pin out for a TX-2B chip


and for a RX-2B
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