Troubleshooting RC Model Truck

[timtenor]

I just bought a used All Bright Hummer RC model for my daughter, and it quit working after one day. I need to get a good book on troubleshooting RC models, so that I can diagnose and repair it. I've done some online searches, but haven't found anything useful.

[Rodney]

I,m not familiar with that particular name of RC equipment. Is it on the 27MHZ channels, the 72MHZ or 49MHZ? Is it AM or FM? Are the servos PWM or just bang-bang? Have you checked out the batteries, make sure they are fresh and polarity correct. Do you have an oscilloscope or just a regular VOM? need much more info to answer your query.

[timtenor]

It's frequency is 49 MHZ. I don't know at the moment if it's AM or FM, I'll have to look at the controller when I get home. I have several multimeters and a scope. The problem symptom is that there is no response from the truck when the controller's controls are actuated. The batteries are fresh in both the controller and the vehicle. The indicator light on the controller shows that commands are being sent, that is, they light up if you shift gears, turn left or right, on try to move forward/back. Of course, I don't know if the transmitter is actually working, or if the vehicle's receiver is faulty. The controller's inputs are simple switches, so this is essentially a bang bang controller.

[toejam]

Try finding allbright's website. I got there using google i think. They may help you more than yuu would expect.

[keymaker]

Is the antenna on the transmitter or in the vehicle messed up??

[timtenor]

The antenna appears to be fine on both items. I have the truck completely disassembled, and have traced the wire to where it's soldered on the board. All of the connections appear good.

[keymaker]

wait
take it bakc
get a new one<p>
sorry thats the best I can do
I'm loaded
:-=)

[rshayes]

You might try making up an RF probe for one of the voltmeters. This would allow you to see if there is really any output from the transmitter. As it is, you don't know which unit to troubleshoot.

[keymaker]

waiit a minute
I am even drunker now
THe amazing part is how clearly I think when I am like this<p>
Here's whas't wrong:
One of the crystals is unplugged or not seated, well<p>god blessme

[Rodney]

You can easily check to see if the transmitter is transmitting RF. Just wrap a wire around the antenna a few turns and connect the ends to your scope input ne side to ground and the other to the hot input. You should see the RF input on the scope. If it is AM, you will see the signal change, if FM you will only see the RF input as a steady high frequency signal. If you are outputting RF at the transmitter, connect the scope to one of the outputs of the reciever. You should see the commanded pulse there if the receiver is working. Check for the signal in front of the actual actuators on the truck.

[Edd]

Sir Tim:
If that unit was in the $70-120 range it typically would use a common/simple am superregenerative receiver design. Was the unit initially operative when you got it ? Its common for the 49 Mhz unit to use 6 different frequencies. e.g.49.830/845/860/875and/890 MHz via plug in xtal swapping. A very select few use a slide switch to rapidly shift to another two or three open frequencies. Is there any chance that this is the case and some rug rats errant little finger toggled it from the mated xmit freq? Is the transmitters control utilizing the joystick configuration or possibly the Traxxas style with pistol grip and trigger and with a small steering wheel on the side.
You may not have one...nor access to...but in the past I typically have used a scanner to quickly check the transmitters functionality. Its hard to misinterpret that tone and its distinctive shift as a change is made with a control manipulation. There are some other units out there that might be brought into play for detection of the xmit signal.
Like using one of the older portable phones that was on the 49Mhz band, Baby room receivers used that freq also, using an older ..(or cheaper)..FM receiver that was not synthesized in the osc circuit and has continuous tuning so that you can seek out the xmitters second harmonic at ~99-100 Mhz. Don’t question the AM/vs/FM intercompatibility…as with that xmitter antenna right against the receiver medium… its carrier is going to swamp that unit and the distinctive modulation will be compatible with both modes. Also you mentioned an ol' silly scope .Take a fully leaded 1N34 germanium…ideally..with its anode to gnd and a .001 cer cap shunting it and the cathode going to a 1x scope probe into the scope at 5mv vert sensitivity. (Okay
a 1N914/4148 on the det diode as next best choice…since you probably wouldn’t have a sm sig Schottky diode) You then use this as a RF sniffer/detector probe against the Xmitter whip as you enact a transmission with a command.<p>Next there would be the receiver proper itself working, considering that by now you had confirmed a functioning Xmitter.
In the past I have checked receivers and even GDO’s by monitoring an Audio sample from the output of the superregen detector of the receiver.That could be with a scope probe or my preference, an audio amp, plus initially its easier to detect aurally
As you were searching for one point amongst a potential 4 or so. Typical receivers are in a plastic box with a cover and all of the PCB’s foil plane is exposed easily upon opening.To familiarize you with a super… ckt use the submitted URL for ref:
http://members.shaw.ca/novotill/RcCarsSimple/
Behold…….its no graphical Picasso but will certainly suffice for our purposes.
On second examination…….. maybe it really IS more Picasso(esque) after all!
Drop down to the pages very bottom schematic,
Most all circuits use this basic RF front end, with slight variances.
The left (2S) C1815 is the RF amp/det isolation stage then the right (2S)C945 is where the detection takes place.What you need to do is have the unit receiver operational and couple an audio amplifiers input thru a shielded line to a short lead length .01ufd cap to the collector of that ‘945…or what number your unit might be using…no difference. The resultant sound should be just like you hear from a FM or TV receiver off of any station….white noise. Activate your transmitter and enact a command and you should hear the tone and its shift acoustically in the received signal.Once you have initially familiarized yourself with this technique…no problem to step up to the scope probe and watch the “grass” until you activate the xmitter and then you can observe the demodulated signal. Past this point, for economy,lately the further processing is usually via a dedicated 14 dip servo driver(s) chip. Much simpler from the old days of discrete and companion H-bridges for indiv servo
driving.
Realizing a different configuration on your receiver and having to enact identification by reverse engineering, keep this in mind. Find where the rec ant wire goes into your receiver PCB and trace the foil til it gets the closest connection into a transistor. That transistor should be the RF amp transistor OR possibly THE detector itself if this was a cheepeee unit. If a RF amp was utilized, expect the next closest xstr to be the detector.Its for certain that the probing of their CBE’s with the cap isolated audio probe will certainly reveal it.
An audio amp..? one might commandeered by connection of a shielded line from a pocket radio from ground to the wiper of the vol control and the rec set off station on AM mode…also there’s the battery powered computer aux speakers with their internal amps, etc
Hopefully this little Ruh-Cee tutorial might guide you onwards to your solution. <p>Then there’s this hub that will put you into the wide wide world on this RC site:
http://s.webring.com/hub?ring=rc_car <p>Pls excuse any typos, as this was processed via voice recog with minimal editing!<p>Plus this was timely with no redundant info on feedback to you only prior to [February 02, 2004 07:20 PM ](which seemed to be the timing of keymakers state of pseudo sobriety)<p>73's de Edd
[email protected] .........(Interstellar~~~~Warp~~~Speed)
[email protected].........(Firewalled-Spam*Cookies*Crumbs)
<p>[ February 03, 2004: Message edited by: Edd Whatley ]</p>

[markcox]

Wow nice reply ed! <p>I used to have some rc cars I remember if you touch the antennas together (can and Control) it would make the car go crazy. Might tell you if it recieving at all. Did you check for crack in the board of the transmitter? Maybe it got droped?<p>Sorry for the lack of technical info im just learning!<p>Mark