MK109 Dice can't count

I did a check and my MK109 does more 2s and 3s than any other number because there are two ways to show 2s and 3s. I checked all the diodes for polarity. Is there an explanation how the display operates as I cant figure it out! Cheers

Please post clear and high detail pictures of the solder and component side of the PCB


Sorry but I don’t know how to put up pictures. I have carefully checked diode polarity and soldering. I did probe IC2 pins and did the following chart.

 Q1  Q2  Q3

1 1 0 0 LD4
2/ 0 1 0 LD1+LD7
2\ 0 0 1 LD3+LD5
3/ 1 1 0 LD1+LD4+LD7
3\ 1 0 1 LD3+LD4+LD7
4 0 1 1 LD1+LD7+LD3+LD5
5 1 1 1 LD1+LD7+LD3+LD5+LD4
6 0 0 0

2/ and 2\ refer to the two ways to display a 2. Thus it can be seen that 2\ is actually a count of 4 and 3\ is a count of 5.

I have the same experience: 3’s and also 2’s are counting much more frequent than others. Is there a easy solution to this?
And is there some documentation how this circuit actually works?
Thanks, Gerard

Hi Gerardq

Having stared at the schematic which I got from the Velleman site … _mk109.pdf I believe the design is flawed!
I think it works as follows.
With a binary count of 1 IC2 Q1 goes high and lights LD4 to display a 1
With a binary count of 2 IC2 Q2 goes high and lights LD1 and LD7 to display a 2
With a binary count of 3 IC2 Q1 + Q2 go high and lights LD4, LD1 and LD7 to display a 3
Here is where it goes wrong:-
With a binary count of 4 IC2 Q3 goes high and lights LD5 and LD3 which displays another 2
It doesn’t get any better!

The use of ZD1 and T1 is I think to light all LDs for a six as there is no other way to light LD2 and LD6.

I think the solution is either throw it away and start again or design a game that has a dice with two 2s and two 3s!