RC10Talk - The Net's Largest Vintage R/C Community

Hey,

I have a 410-Mxc with a bad FET I think. Works great until about half throttle then the power drops off considerably and the motor starts doing the "funky chicken". I have tried to find some schematics but Novak holds them pretty close. I am not bad with electronics but trying to trying to fix this without schematics is going to be a challenge.

Does anybody have any experience fixing these or schematics or advice for checking the FETs?

All the forward FETs are tied together in parallel. I would think that if you loaded the motor down, ie, put it in a car or some way to load it up(maybe a slave motor), and apply throttle, you might be able to tell a difference in temperature in the row of FETs. If they all heat up except for one, I'd suspect that one. If only one get's smokin' hot, then I'd suspect that one also. The gate drive could also be messed up in some way.

someone here wrenched on his own custom speed controls. i can't remember his name. let me see if i could dig him up.

Well with the transmitter off the speedo goes to full throttle and runs strong. So the FETs are probably ok. It must be something in the control circuit.

Does anyone know the control voltage from the receiver?

the control signal from the receiver for a standard servo goes from 0 to 5v in a pulsed fashion. About 50 cycles per second, and the pulse width varies from 1 to 2 milliseconds with 1.5millseconds being 'center'. lots of variability there, and also, this is for an analog servo. it's certainly possible that the receiver is messed up, OR the control circuit in the esc is bad in some way. try putting a servo on channel 2 and see if it can be controlled smoothly. that will determine if it's the receiver or the esc.

Ok. Bummer. I was hoping it was an analog voltage so I could hook up a power supply for troubleshooting. I know the RX is OK. I have been checking all my speedos with the same receiver and this is the only one thats acting up.

have you taken the case off? I've found that sometimes just an inspection of the PCB can give you clues to what's happening. broken component or lead or dark mark or smoke mark leads to what's bad. You might find that the power wire or control wire, or even ground wire is barely hanging on by a strand or two.

Yes I have. Everything looks OK.