Troubleshooting 72MHz RC Systems

Sometimes, you plug everything together and it just doesn't work. In this case it's good to be able to figure out what part is broken. Here is a step-by-step guide to help you figure it out. I assume that your radio is transmitting, and if it's not there really is no way to know. If none of this stuff works, you can assume that your transmitter is at fault, but that's usually the last thing to go wrong. This guide only applies to 72MHz systems with electric motors, and assumes that all your parts are quality parts. If you have low-quality parts, the first thing you want to do is replace them with higher quality parts and see if that fixes the problem.

First, plug everything together like in this video:
RC Wiring

OK, now what is the problem:

Servos don't move and motor won't start:
1. Possibly "transmission not received" - see below
2. Check the battery with a voltmeter - should be 4.2 volts per cell if using Lipo, and 1.2 volts per cell if using Nicad/NiMH. Charge it up if it's not fully charged.
3. Make sure the ESC is properly programmed for your battery type.
4. Try using a receiver battery on the receiver. If this works then you probably have a bad ESC, or the ESC does not have a battery eliminator circuit (BEC) or the BEC is not functioning. Replace the ESC with a new one that has a BEC.
5. Try reversing the plugs into the receiver on the servos and ESC. They won't work if plugged in backwards, but it won't harm them.


Servos work but motor won't run:
1. Check all the connections with an Ohm-meter. Make sure they are tight and conducting.
2. Make sure the motor isn't shorted or damaged. The easiest way is to try another motor that you know works properly. The other way is to test it with an ohm-meter or testing lights. For brushed motors, you should be able to run current through the leads and there should be no current between the leads and the housing. For brushless motors, there should be connectivity between each of the three leads to the other two, and no connectivity between any of the leads and the housing.
3. Try reversing the throttle channel on your radio

Motor runs but servos don't work:
1. Try reversing the plugs on the servos into the receiver.
2. Try different servos.
3. Try the same servos in different channels.
4. Try replacing the ESC - if this solves the problem then your ESC is bad, or it does not have a battery eliminator circuit (BEC) and you will have to use a different ESC, or use separate battery to power the receiver.
5. Try using a receiver battery plugged into the receiver. If this works, then again, your ESC is bad or its BEC is not functioning or it doesn't have a BEC.

Motor starts and stops or servos randomly move:
1. This is almost always a sign of "transmission not received"
2. Make sure the transmitter is on full charge. Some radios will have a very weak signal when the battery is down to 60-70% charge. Make sure it is charged up all the way.
3. Pull the antenna up on the transmitter and see if this helps. Make sure the antenna is screwed tightly into the base.
4. If you've done all that and the signal is still not received, continue in this list.
5. Check the receiver antenna. It should be fully extended, with no loops, and should not be touching any metal parts. It should be firmly soldered to the receiver.
6. Check the receiver crystal. It should be pushed all the way in and taped in place so it doesn't jiggle loose. Loose crystals are a common problem.
7. Check to make sure the channels are correct. Your radio will have a channel number on it somewhere, like "72.150" and the receiver crystal should have the exact same number marked on it. If these numbers are different, nothing will work and you will have to replace the crystal with one for the correct channel.
8. Replace the receiver and crystal with another one. If this does not solve the problem then it is likely that your transmitter is bad. Send it in to the manufacturer and have them fix it. You can not service your radio per FCC regulations. Don't even try it. To confirm that the radio is bad, you would need another one on the same channel, which you are sure works properly, and test to see if the signal is received from that one.


This guide only covers the most common problems, and there are many other things that can go wrong. If you haven't checked all this stuff though, please check it before you post a question on a forum. I will add things to this guide when I discover them, so please let me know if there's a problem you can't fix.

Over and out!
Jasmine