I'll (quickly) describe what happened to me on my HL King Tiger. After an hours run on grass and sidewalks the tank started acting up. Would go forward and back but not turn. "Ah the boards burned up" i figured. I assumed that if the transmitter ever went bad it would act like and off and on switch, simply quit sending signals and, no movement from the tank. Well this isn't the case and it took buying ANOTHER tank for me to find this out (the hard expensive way, by upgrading the KT from the older TK01 board used in the non S and S, to RX18 before i really needed to-i don't really mind if the tank doesn't have smoke and sound).
Image above shows the NON smoke and sound transmitter. This one works with HL tanks which will be fitted inside with the circuit board designated "TK01" (it says as much right on the board). The visible difference is it has a switch, shown by arrow, to change frequencies.
And above is the SMOKE AND SOUND transmitter (this works with the RX-18 board, this board is different since it is enclosed in a two piece plastic box into which, electrical plugs for the tanks functions fit. Many people add a fan to their rx18 box by gluing, you can also buy a special circuit board box with fan equipped from welsh dragon in the UK- for about $50 US).
Arrow in the image shows the holes, where the crystal gets plugged in. Crystals come in pairs, a similar crystal of the same frequency gets plugged into the receiver board of the tank.
Unfortunately these two transmitters do not interchange and there is no way to convert one to another as far as I know.
....So my new tiger 1 arrives and i already have charged batteries in my old transmitter from the King tiger; they are the exact same types of transmitter so, i tried to use the old one on the new tiger. Lo and behold the tank started going bonkers same as the KT had-could not turn, could not stop, had to reverse to avoid crashing etc. So i took the new transmitter from the tiger and of course THAT one worked fine!
Instead of spending maybe over $100 on transmitters, duplicate wiring sets, fans, wiring, RX18 units etc. i could have fixed the KT with a $45 transmitter from Aliexpress...
It did cross my mind the transmitter could be bad but i just ASSUMED..it was the circuit board (and it wasn't). And this was an expensive assumption!
Of course a lot of people will not have the luxury of a spare transmitter to test their tank if it quits; and i'm not sure how you'd test the transmitter anyway but I'm guessing it could be done with a regular old multimeter. I guess you could remove the screws, pop the back and measure voltage at the contacts as you move the stick, perhaps that might work. But a lot of the contacts inside the transmitter are hidden-you'd have to take the entire thing apart not just the back.
And here's what you will see if you try to take the transmitter apart:
Ready to try to tear into that and fix it? Neither am I! New ones are $30 on aliexpress...
Some other things i noticed about transmitters:
NEVER SLAM THE BOX TO GET THE BATTERIES OUT....I'm thinking this could have damaged the internals. To change the batteries always pry them out, with ANYTHING (but probably a wooden or plastic object might be best). Never slap the transmitter box on purpose, try not to drop it, put it away where it is not likely to fall or get kicked by someone. After learning the hard (read EXPENSIVE) way I now know, transmitters are delicate-ask me how i know... "Handle like eggs" as the old saying goes!
Also if your batteries seem to fit in loosely, don't forget, the contacts in the battery bay could be too loose and not giving the transmitter full power-whether the light is on or not. I'd shim them with a piece of copper wire or something if any of them seem loose.
This can be checked by removing the battery door on the transmitter, and trying to drive the tank. If it wont go, reach underneath and manipulate the batteries a little- roll and push them a bit and see if the tank now responds even for a moment. If the tank then works-some of your batteries are probably making poor contact in there and perhaps stretch the spring, or shim the contacts with something perhaps a bit of copper wire or the like.
MODIFYING THE TRANSMITTER FOR BETTER BATTERY CONTACT
After being bothered by intermittent transmitter performance here is what i did. There are plastic battery divider bits added to the battery bay of the HL transmitter, that separate one battery from another, in the middle of each row. Well in my opinion THESE CAN CAUSE POOR BATTERY CONTACT and transmitter malfunction (whether the light is on, or not!)
As describe above, i figured this must be the case, as when the tank would conk out, i would remove the battery cover, and fiddle with the batteries while watching the tank. Pressing this battery or that one invariably brought the tank back to life.
So i decided to just get rid of those battery dividers as they serve no purpose! I used a dremel. The results are not pretty but i didn't cut too deep and mangle the transmitter. I believe you could do the same thing, with an exacto blade, just chip away at the plastic.
Now i am STILL having trouble sometimes but much less. I figure a piece of thin foam rubber sheet in the battery lid may press down on the batteries..
