RC toy not working if the transmitter is far away from toy car

My son hav a cheap RC controlled toy car which was working well. right now the toy car in not working unless I hold the transmitter extremely close to the toy. I had checked the transmitter with another toy car of same frequency(27Mhz) & its working fine . does the toy car lost its designated working frequency?
there Is a small coil with few turns , not waxed. I read in a blog that, the changes in the turns can cause shifting of operating frequency.

awaiting comments....

Most likely it is very sensitive to being dropped and is de-tuned. So adjust it with the care of tuning a piano string.

I have another toy car receiver board which is working in same frequency range, is it ideal to replace the coil with another one ?

No, you will alter the characteristics of the replacement. These cheapo receivers use a circuit (superegenerative), that uses a tiny feedback capacitor to set the level of sensitivity. This too could change in value due to vibration and will make an enormous difference in the sets sensitivity. of course any component could have gone faulty! Try using Google- "remote control car circuits diagrams", there are a great number of circuits, try and figure out which is closest to yours.
Frank

Maybe it's just a bad/broken connection between the receiver and it's antenna.

[QUOTE=chuckey;1413152]No, you will alter the characteristics of the replacement. These cheapo receivers use a circuit (superegenerative), that uses a tiny feedback capacitor to set the level of sensitivity. This too could change in .../QUOTE]

yes exactly... I had replaced the coil. but no effect. . and put back the old one. I tried to tune the coil carefully but this also had no effect. now I need to touch the receiver antenna terminal to get things work else the toy car wont make any moves!..

Detecting the fault requires debug experience. It could be cracked trace or solder joint or anything really.

i dont have any experience in circuit debugging.; (

I removed four transistors from board(A) which I mentioned in the question to solder it in another faulty board(B), whose transistors are faulty(i m sure), now that board(B) is working well except it doesnt steer the car towards right.

I curiously connected the board(A) ( without transistors) bingoo! its working! . the four transistors I removed was used for switching the polarity for steering motor. now I connected back all the four transistors.. it worked for sometime and went back to the state I mentioned in the question :(

why does this happened!?

This is called "buckshot" fault finding,just changing components at random. Have you a DVM or a multimeter. without these you have not got any hope of finding the fault. One good fundamental step is to look at the board with a magnifying glass and carefully check the soldered joints for a dry joint. This is where the component lead is surrounded by solder but is not actually attached to the solder. You can sometimes see a small circle around the component lead and pulling the component, the lead under the board will move within this circle. Or you can just resolder all the joints!
Frank

It worked for a while? With the transistors re-installed?

On first reading, I thought one of the transistors must be shorted. Because you state it worked without transistors.

Testing them all would be a good idea. There is a simple crude test which is easy with an ohmmeter, when the transistor is out of circuit. Did you do this test on your transistors?

Or maybe the transistor's operating characteristics have changed. So it depletes the battery more quickly. Are you watching battery voltage all the time?