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SCX Xenon lights not working

26987 Views 107 Replies 31 Participants Last post by  RACING LINE

Having recently purchased my first Xenon powered slot cars, the SCX Aston Martin and Seat Cupra, I was looking forward to some fun night racing.

I gave the cars a few daytime laps and was very impressed with the brightness of these bulbs.

Anyhow, darkness arrived, but shock the front lights on the Seat had given up and the Aston only had one working. Race abandoned due to bad light!!

Is this a common problem? Could it be just a bad connection?

Thought it would be best to ask those in the know before taking my trusty screwdriver to them!!

Any pointers would be greatly appreciated.

Many thanks and regards

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Carrera's raced against Carreras are superb. Great lights and they are dead quiet.
Plus you can get a pair for £30 on ebay very very easily.
The Ferrarir 575's are superb.
Steve A, you can check the LEDs by putting a low voltage (3V) across the LED legs.

I'm not sure about repairing the board, it looks very tight and I'm not sure my soldering skills are up the job (my DBR9 blew its lights too). I've ordered an overdrive XDS kit instead, so hopefully I'll be able to get the lights working again, and they'll be permanent.

Another thought too, really as a preventative measure to try to stop this happening again in the future. Would it be possible/ make sense to put a resistor in before the board? If the lighting board is only getting 12v then hopefully the circuit will survive. Can someone advise on values?


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It's a bit tricky to check the LED's. However if they have glowed brightly at any point then they have probably failed, if not then they are probably ok. It all depends on how the transistor failed. If it failed short circuit then it will probably have taken out the LED's, if it failed open circuit they will probably be ok.

Sorry there is not a simple answer. No I did not buy a SCX as I have a bit too much on at the moment.

However if you want send me your car I will have a look, and replace the transistor, check if the diodes are ok and send back for testing.

Regarding the 16v, 14.4v, 12v thing, are we sure we're talking about the same/right thing?

Disclaimer: I could be wrong here, since I don't have the bits in my hand!

The Scaley wall-wart does pump out 16v, but isn't that alternating, rather than "direct" as-it-were. Surely there's some rectification circuitry in the powerbase before the controller comes into play - and it's from the downstream side of the controller that voltage gets applied to the track and from there to the car.

Rectifying down 16v alternating will inevitably lose "ultimate" voltage, so reading what it says on the transformer isn't going to help (and I don't know if it says if it's peak or RMS - if I remember my terminology correctly!). And depending on the sophistication of the rectification and smoothing circuits, that loss may vary between manufacturers.

Surely, reading the constant voltage at the track with the controller fully depressed is the only sure way that you will get the maximum that will be applied across the lighting board?
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Rich G thanks for your very generous offer, I will be happy to cover all the postage and cost of transistor thingy. Please PM Address if you could have a look, but will fully understand if you have other commitments.
Seems important to find out the truth about the new SCX lights as more purchases under consideration (360 and CS6R). I imagine lights are little more than novelty to the club racer, but on our home circuit they really add something to "Le Mans racing" with my son.
From a different angle, if the LEDs are still good but the transistor is blown, could the LEDs be wired directly to the lighting output of Scaley digital saloon chip. This assumes the chip has all the required diodes, resistors and transistors etc incorporated in it. Hope this makes sense as electronics is not exactly my field (driving fast boats is my job, 40,000bhp and steering wheel 2" in diameter).
Hi Steve

Just to let you know, car arrived safely this morning.

Have had a look at the front light board and the transistor is obviously blown, it has that telltale bump in the top.
That is however what we were expecting.

SCX have not exactly designed the board for easy removal as some of the plastic parts are assembled after the board is put in. However I have just managed to extract it without removing the plastic parts.

Have tested the LED's and the good news is that they are both fine.

To be continued....

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Progress report. Removed the transistor and replaced with beefier one. Switched on but no lights.
Checked the other components and the zener diode is short circuit.

Am suprised that the zener has gone, had better do the maths on that as well. I guess if they can get one component wrong, they could get them all wrong.

Quick bit of maths shows worst case of about 50mW so should be fine assuming this was a 100mW zener, trouble is I don't understand the markings.

From the measurements that have been made looks like a 4.7V zener is needed, unfortunately it's about the only value I have not got.
I will be ordering some other components next week so will get one. However means that getting the board going will be a few days away.

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QUOTE SCX have not exactly designed the board for easy removal
concur 100% having hit 43 and bought my first pair of specs this year, soldering any thing on that board is out of my league. No hurry to return car and happy to pay for anything required to get to the bottom of the SCX malaise. Best I log off now, having upset Jexy with comment about magnets for Slot Rally GB made in jest. (The guy is a hero and hope is good work will be continued in future years).
Keeping a very low profile
Bits arrived from Farnell this morning so have completed the repair.

Fitted a BZV55 series zener, 4.7v 400mW (Farnell 305-0919)

I do not know why the zener had failed, worst case dissipation is only 50mW and it should see nothing like that. The transistor failing would not put additional load on the zener. Also the zener had failed short circuit so that would not have caused the transistor to blow. A mystery.

Fitted a ZXTN2031 (Farnell 108-4421) in place of the failed BC817

There is no mystery here why the original device failed. It is rated at 250mW and even with 12 V on the track will be dissipating 280mW at 16 volts the dissipation will be up to 600mW.

The replacement is rated at 1W however in practice will be less than that because of the very small heatsinking from the circuit board. (I would prefer a higher rating, but this was the best I had) Hopefully will be ok, I ran it for 30 mins on the bench at 16 Volts and it was Ok, but it needs Steve to thrash it round the track for awhile.

A question for anyone with the body off. The pictures earlier in this thread show the transistor as a 6C which translates to a BC817. The device I removed from Steve's car was burnt so I could not read the marking. Would be interested in what marking is on other transistors.

So final thought. I don't know if people from SCX read this forum? If they do then there is a major problem with your light board, I would expect you know this by the number of returns you get.

A comment would be nice, failing that if anyone has a suitable name / address I will drop them a line.

Final Final thought. The connections for the lights and the floating motor all just use copper to copper strip contacts. To my eye this looks like "Optimistic Technology". Do people have any problems.

Steve will put the car in the post tommorow.

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I got a new SCX Aston yesterday, very nice car, but...I went to true my tires in the normal way (setting car backward on track with sandpaper under it, while holding both with one finger) and the the front lights went POOF! The rears still work fine. This is on a Scaley Sport with stock power. Also there was a bad burning smell. They were nice and bright for the first few laps before truing. I don't really care about lights that much, or I'd return it, but I have some very old SCX cars with lights that work fine. Is the reverse power a problem for this system? I didn't see any obvious melted stuff on the board. Why does the front board need all those little gizmos, while the rear light board has almost none?
The easy answer PeteN is - yes, reversed the lights didnt like it or rather, the basic as a caveman board didnt.You have burnt the resistors most likely
Basically SCX lights are so bright because there is no protection between track and the LEDs which is why they burn out so fast on crashing etc. Power surge does it, or overload when in reverse.
I will say it again at the risk of repetition...

Replace the SCX board with aftermarket like Overdrive or Slot.I which DO provide circuit protection, you won't regret it.
Swiss it's as if you have ignored the whole thread.
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Why do the rear lights still work and have an almost empty board? Why can't they just get some of the rear lights in clear for the front?? By the way, the car handles beautifully!
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QUOTE (RichG @ 21 Sep 2006, 18:21) <{POST_SNAPBACK}>Swiss it's as if you have ignored the whole thread.

Probably because I did
Missed the entire first page sorry chaps!

I'll go away again
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OK, I don't think the reverse polarity had any thing to do with it. I ran the other SCX car that I bought with the Aston, the new Seat Red Bull touring car, and the head lights burned out within 10 laps running only the normal direction (non mag). Burned smell again, tail lights still work fine, same as Aston. This time they flickered for a couple laps, then were gone. I must assume the Scaley power (16v?) is a touch higher than the SCX (14.8v?) and the headlight circuit is just built with very little safety margin? Shame, car handles very well with an interesting new motor pod design.
QUOTE (PeteN @ 22 Sep 2006, 15:57) <{POST_SNAPBACK}>I must assume the Scaley power (16v?) is a touch higher than the SCX (14.8v?) and the headlight circuit is just built with very little safety margin?

Why dont you read the thread Pete?

So Rich, is there an easy fix that us mere mortals can use?

I put the meter across my scaley-powered track and got 16v, even 16.5v, at full throttle. Would a resistor placed before the light board work to protect it? Or does it need a more in-depth fix? I think fixing blown boards is probably beyond most of us, but if there's a relatively simple way of preventing it happening we'd appreciate it.

I just bought the SCX C6R, great car, really good fun to drive. But the lights lasted 4 laps and then went 'pop'!


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Good question Rob.

There is a bit of me that says you should all send them back to SCX and get them to do something. The board is not fit for purpose and my calculations show that I would expect it to fail in most circuits, not just higher voltage ones.

Does someone have a name or a contact at SCX? If so I will drop them a line explaining the problem. Although I feel they must know of it already, surely some people must return cars?

To your question, a simple solution. Probably first thing to try would be a series resistor. My concern is that by the time you had put in a suitable value to protect the board, the lights would be a bit dim. I will need to do some maths. An alternative might be a series zener, as this would drop a constant voltage.

When I get home at the weekend I will give some thought to a simple mod.

It would be very much appreciated, Rich!
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