SCX Xenon lights not working

OK I've done a bit of Ohms law and I think the simplest solution to the transistor blowing is a 100 ohm resistor soldered in series with the +ve feed to the board ( this is the left hand side copper strip with the body upside down bonnet away from you).

You will need to unsolder the strip from the board, bend up a bit and then solder the resistor to remake the circuit. An alternative if you are happy to do it would be to cut out a short section of the copper strip and then solder the 100 ohm across the gap to remake the circuit.

At the moment the cars lights will get to full brightness at about 6 volts on the track. The modification will mean that you do not get full brightness until about 10 Volts. The resistor will need to be a 1/2 watt. Maplins, Farnell. RS all will have them. The resistor should drop between 3 and 5 volts depending on you supply voltage and should save the transistor.

The mod will of course only work to protect a functioning board, it will not mend a failed one.

The above is all theoretical so needs someone to try it out and confirm that the transistor does not fail and that the lights still get to full brightness albeit at a higher track voltage.

Rich

Hey Rich, Thanx a lot

We have done the mod you suggest to a new car, and have completed over 20 laps, and shock horror the lights still work. Normally scx lights give up the ghost after about 3 laps.

A pic of how we followed your instructions:
A single cut, and copper strip bent out of the way, resistor soldered, bridging the gap.


Not sure if that resistor is correct, but it works.
The lights are slightly dimmer at low throttle, but only very slightly. And if that means they are gonna work for longer, then that is a fair trade.
Nice on Rich, thanx for taking the time If this is the solution, then it is a well worth while 5 min fix.
We will keep you posted as to any developments.

Thanks Rich

I've now got three SCX cars with blown front light boards so I've been playing around with some LEDs and resistors, trying to find a cheap fix.

I had no intention of trying to repair or modify the boards, so I just removed the intact LEDs and binned the rest. I left the rear boards alone.

The LEDs I bought are rated at 3.3v, 20-30mA. I'd previously recorded a peak of 16.5v at the track from Scaley wall warts, so I did some maths (well MS Excel did the maths!) and came up with 330 ohms for 30mA or 495 ohms for 20mA needed for two LEDs in series.

The LEDs came with 470 ohm resistors so they seemed like a good starting point. I soldered the resistor to the +ve leg of one LED, then soldered the +ve of the second LED to the -ve of the first. This 'circuit' was then attached to the existing copper tabs in the body. I did my Vette and F360 like this. I also found some 560 ohm resistors, so I fitted one of those to my DBR9.

The 560 ohm resistor was a mistake. Running the DBR with no load the lights work fine, but on the track they're hardly coming on at all even at full throttle.

I did about 70 laps tonight with the C6R and it's been great, and it still works! So my cheap 'n' cheerful effort has so far lasted nearly 20 times longer than the original SCX board! The lights come on from about 1/3 throttle, gradually getting brighter with more power.

I did about 30 or 40 laps with the Ferrari and that too was fine. But, and here's the rub, it's very easy to damage the circuit. I put the Ferrari on the other lane, forgetting that I'd reversed the track power. About a second of going in reverse, and suddenly only one LED works. Oops!

So I've got some repairs to do, but I'm pleased with the results. I just need to remember to put the cars on the track the right way! The LEDs weren't expensive, £4.45 inc post for 10 LEDs and resistors from an ebay seller.

No pics yet, but I'll post some if you want 'em.

cheers,

Rob

Nice one Rob,
Yes pix would be great please. I could then think about fixing my pug.
QUOTE The LEDs weren't expensive, £4.45 inc post for 10 LEDs and resistors from an ebay seller.If you have a spare pair Rob, i would gladly PAInPAL you an amicable ammount? If you don't have spares, would you be so kind as to provide a linky, to the seller please.

Another 30 laps with the Fiat, and still working fine. Cheers Rich.

Ok, you asked...





Sorry Kev, I haven't got any LEDs left but here's the link to the seller

Rich, thanks for the diode advice What sort of diode am I looking for? Just had a quick look on ebay and I am LOST!! Wouldn't the diode cause a voltage drop and thus affect the resistor calcs though?

cheers,

Rob

Oh right, the whole front board is gone!! Super job.

Cheers for the pix, and linky, Rob.

I think i will be able to manage that. Nice one Rob.

QUOTE you should consider putting a series diode with the 470 ohmRich, Do you know where i might find these on the net, please? Any linkys?

found these one's, are they any good??
If so, How much would the resistor value want to be with these in series?

edit: I see Rich listed this model in the last post. sorry.
My resistor Q still stands though.

If anyone wants a few, just drop me a PM. I don't think i will need 100
Rob, i will fire some your way, once i receive them.

Using Robs figures which were
2 LED's in series =6.6V
Input Voltage 16.5V
20 mA
Series resistor = 495 ohms
Nearest value = 470 ohms

Add the volt drop of the diode 0.7V
New series resistor = 460 ohms
Nearest value 470 ohms

Back where we started.

If the LED current was allowed to rise to 28mA then series resistor would be 390 ohms, choice is yours.

Rich

Thanks Kev, much appreciated

And thanks for the calcs Rich. The voltage drop would seem give the LEDs a bit of a safety margin too, which has to be better.

cheers,

Rob

The latest stage of this little saga - on Rich's advice Zipp bought some diodes, and cos he's a nice guy he sent me some! Thanks again mate

So I had to try a couple out, didn't I? Here they are fitted to the Vette and 360. I put the arrows in cos the diodes are tiny



I haven't tried them on the track yet, but the lights work fine at 9-12v, and nothing went pop when I reversed the current so I think that's a successful test!



Total component cost is under £1 per car, so I think I'm going to be adding lights to a few more!
Rich, we need a capacitor next so we can have permanent lights

cheers,

Rob

Neat job. Now you'll end up cutting up all your best collectable cars to fit lights (I did!) First Fly Viper with lights (Viper A1) First Ninco car with lights (Green Merc DTM) etc etc. now worthless but they have lights

What an inspiration this thread has proven to be. Just bought 20 white LEDs frm the source mentioned by Taxi, awaiting diodes. Impatient to get this project off the ground, my understanding is that the diodes are just there in case the car is placed the wrong way on the track. So my very limited knowledge of electricity (electronics?) suggests LEDs use very little current, what if a 12v battery is placed in the car?
This would then require a switch to turn lights on and off. where would you source a tiny switch suitable for a slot car? again answer is on another thread. Carrera have very kindly put one ready on all of their cars, and they run better if the guide is wired directly to the motor.
So put all the info from the various threads together
1. Cheap Carrera Bentley (TK max Canterbury have Le Mans Heroes set @ £29.99).
2. Buy 20 white LEDs (arrived with resistors).
3. Unsolder guide wires from switch and attach to motor terminals directly.
4. Find old small 12v battery (smaller than AAA) in cupboard.
5. stick it all together. Battery hot glued infront of driver's footwell. Wires from switch attached soldering one end to battery terminal (does this damage battery?).

IT WORKS
Even for a non electrical person like me.
Result bright permanant lights, should not blow if used on scaley track, car can be found after crash and would be ideal for night photography

Down side, car now weighs in at 107gms.

Thank you Slot forum, at least 4 threads have come together to inspire me to give this a try.

Will fit some of the LEDs without battery due to weight when diodes arrive.
Now if I fit 4 LEDs at front can I do that without resistor, and will it lead to meltdown (or more likely snow blindness as 2 are bright).

Here you go -

Replacement lights
3mm white LEDs
470 ohm resistors
1N4001, 1N914 or 1N4148 diodes

I bought my LEDs here, he supplies them with the correct resistors too.

Try here for the diodes

The 'preventative' resistors are 100ohm, the first seller lists them as well.

For permanent lights try the excellent Overdrive kits, from Pendle, MRE etc

cheers,

Rob

Hi Guys,

Read this thread with great interest. I have two SCX cars, Solberg Subaru WRC and Ford Fiesta JWRC, both of which suffer from "dodgy" lights!!!

So I've just bought the above parts from Ebay and will hopefully be able to follow the piccies and finally get this annoying prob sorted?

Definitley will not be buying SCX again until this is finally sorted by them!!

Thanks so far for all the helpful advice.

Nitemare