MK 100 Christmas Tree Help Needed

Hello Dear Forum Members,

I recently bought and built 18 MK100 Christmas Trees as presents for family and friends.
All but one tree works exactly as they should. The one that doesn’t work as it should has the following symptoms;

LEDs 1, 3, 5, 7, 11, 13, 15 are flashing
LEDs 2, 4, 14, 16 are on but NOT flashing
LEDs 6, 8, 10, 12 are not on at all.

Looking at the circuit diagram supplied with the trees it is easy to see that all LEDs on the left hand side of the diagram have problems and the LEDs on the right hand side of the circuit are working as they should.

As I have no test equipment here is what I have done to try and resolve the problem;
Thinking C1 could be the problem – I replaced it with a new one – Result = No Change
Soldered the original C1 back on
Replaced C2 with a new one – Result = No Change
Soldered the original C2 back on

I thought, surely it must be T1 or T2 causing the problems?
I replaced T1 with a new BC 547B – Result = No Change – left the new transistor in place
It had to be T2? – I replaced T2 with a new BC 547B – Result = No change - left the new transistor in place.

Highly unlikely to be a resistor problem?

I have checked the polarity of each LED and they are all correct – I am at a loss now. I don’t mind just scrapping this tree, I realise it doesn’t cost much, but I am eager to learn as to why this could be happening I would love to be able to find the fault. Any suggestions would be much welcome.

Thanking any and all replies in advance.


Could you post pictures of the top and bottom side?


I’m not sure how you checked the polarity of the LEDs.
However one installed wrong will cause this problem.
Since you have a good working MK100 look through the side of the LEDs.
You will see a flag inside match the working one with the non working unit.
As VEL337 asked you should post a clear picture.
An open trace will cause this type of failure as well.

Thanks Wrong-Way. I did check the LED 3 times, but I will check them again.

Thank you VEL337.

This is my first time on this forum so please bare with me if I make any mistakes. I have provided links to pictures of the FRONT and BACK of the tree with the problem. Sadly in my festive season tradition I sprayed all the trees I built in Green before adding the LEDs so the front picture will not be much help in viewing the components.


bazaar553 uploaded this image to


bazaar553 uploaded this image to

Thanks again.


Addding new photos below …


Happy New Year to All,

Dear VEL 337 now that you have seen the pictures, any ideas on this issue please.?

Thank you.


Hi Alfonz

Happy New Year to you too.

The solderings look OK
Apart from the cut trace
Please check those

I saw that line too… I thought maybe the track line developed a fault while being made.

So, to test this I soldered a link wire on to the bottom pin in the red circle to the 3rd pin from the top of the tree basically re-creating the track link between those two points.

Result = Made no difference…

it is a total mystery why only one half of the circuit work fine but not the other…

Would you like me to post it out to you for a closer look…? I would love to know what the fault is…?



Detail pictures are always welcome =)

Or maybe I will just give up on this.? :frowning_face:

Sorry VEL337 - I meant - mail out the actual circuit board to you .?

That’s also possible.
Here’s the address:
Please return the unit to:

Velleman Projects Repair Dept. c/o VEL337
Legen Heirweg 33
9890 Gavere

Thank you VEL337 I will do that tomorrow. Al

Dear VEL 337
Thank you for sending back the circuit board.
There was no message with it. Would you be able to tell me what you found to cause the problem for future reference please.?
Thanks again. Al


I checked with the repair departement. And apparently there was a broken trace.
It was fixed and sended back.

Best Regards,

I’m having a similar problem with an MK 100 I built yesterday and which worked perfectly until today.

LEDs. 1,3,5,7,9,11,13,15 flash

6,8,10,12 are permanently on

2,4,14,16 off

What should I check? My soldering is good - I’ve been building electronics for more than 50 years!!