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rc car no longer accelerating? Answered

alright, so ive got this rc car, it runs off of a 7.2v battery pack and has variable speed and turning. it is not a hobby-grade car, but it is still something id like to hold onto.
today, when i tried to drive it, i discovered it could not accelerate, forwards or reverse. it can steer fine, but trying to accelerate does nothing.

ive ruled out the controller and the motor, which means the h-bridge and associated circuitry must be to blame.
i tested the battery in another car of the same model (not mine), and all was well there.

the h-bridge must be PWM controlled in order for there to be variable speed, so heres what im figuring:
the motor is making a clicking noise when i pull the trigger on the remote, looking at the motor, it is turning very little and then stopping and then doing this again, at a fast rate. when it stops turning for that split seond it returns to the original position, because it has turned so little. i know the motor itself is fine, because i connected the battery straight to it and it spun up and turned the wheels.
i have a feeling the issue lies within the PWM control. i cannot guarantee the receiver chip is fine but it seems kind of odd that it would be the part to fail; regardless i cannot find a datasheet using the numbers on the chip.
if i were to try and look for an issue/failed part somewhere, where might you guys think i should start? there are a number of transistors on the board around the h-bridge, some capacitors, and a lot of resistors as well. i checked all the resistors inside the h-bridge and they are all the same value as the bands indicate, andthere are no corroded or cold solder joints. i plan to test the h-bridge on its own once i find a diagram i can reference to, that way if the h-bridge works i can rule it out and narrow the possibilities.

if you need any more information please let me know.

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steveastrouk
steveastrouk

8 years ago

You really need access to an oscilloscope to check it, but I think the Hbridge is dead.