SCX Xenon lights not working

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?

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).
Regards
Steve

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....

Rich

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.

Rich

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.

Rich