Velleman project?

Question:I recently purchased a "Soldering starter kit" which contained a soldering iron and two electronic kits, one of which was an LED switch thing that lights up two LED's, one lights up first and then the other (it has another name but I can't remember what the hell it is)...and that worked flawlessly, the other kit however, the MK103 featured here http://www.velleman.be/ot/en/product/vie... refuses to work, I've checked and rechecked all my soldering and can see NO problems whatsoever yet it still won't work, it lit up briefly when I knocked something but it refuses to do it anymore, what could be the problem? I'm REALLY frustrated by this so any help would be appreciated.

Answers:
Congratulations in getting into real electronics , Don't be disappointed by you small set back.

When trying to debug a circuit it is useful to do two things first.
Determine what is working and what isn't., and , , never assume anything.
Whatever part of the circuit you can not guarantee is working then you have take it that it is NOT working.
What you think is not working will need careful examination.

If you are very sure that the led's did light up even for a moment you can conclude that LD1-LD4 are correct.
As probably would be R5 , R12 , T4 and R9., and of course your battery polarity.

Unfortunately from this point it is hard to guess where any fault could be.
So you now have to check every part methodically.

Get some tippex or nail polish and put a little dot on each components as you gaurantee it is rite.
That way you will see your progress and you wont miss a part or waste time checking things twice.

Look on the tracks side of the board for bridged tracks or dry joints.
These are common , very common if the board artist made the tracks too close together.

Check the resistors 1 by 1 to be SURE that each one is in its correct spot.
In that kit you have 47ohm and 47Kohm resistors and these look very similar on the color coded bands , so particular attention to these ones ., likewise the 100k and 10k ones.
It would be an easy mistake to accidently swap these ones around.

Then move onto the capacitors , and double check to see that the electrolytic capacitor is around the rite way.(it probably is)

Finally the transistors.
Check to be absolutely sure that the 3 BC547 transistors are in their right spot and that the CBE legs are in their right holes.

Double check to see that the T4 BC557 is likewise correct , but it probably is if it did light up for a moment.

I hope things work out for you..

gW:-)

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