Edu08 occiloscope

When switched on the screen lights up with instructions to press the menu button which I do but nothing happens.i have checked the switch and it is working OK.

Please check the voltage on pin 17 of SK1 on the top board.
When no button pressed, there should be 0V.
When Menu button is pressed, there should be about 0.98V.

You can use the black test lead as GND reference.


Pin 18 (as circled on the picture) is 0.98 volts when menu is 17 is 3.34 volts when pressed

Seems to be OK.
Yes, I meant the circled pin of SK1.
Next test:
Check the voltage on pin 3 of IC3 on the bottom board.
Check on IC leg to identify possible IC socket defect.
When Menu button is pressed, there should be 0.98V.

Pin 3 on ice is 0.98v when menu pressed.
If it’s any help zd1 reads --1.05 instead of --5.0v

It seems the microcontroller IC3 is not recognizing the input “command” from the button. IC3 may be defective.

This may indicate the ZD1 is not OK or the charge pump around T1 and T4 is not working properly.

You may use this image as a reference to check the voltages:
The circuit diagram is for EDU09 but it is quite similar to EDU08.
There are different reference designators.


The voltages should be:
A = 1.67 V
B = 0.44 V
C = 4.40 V
D = 3.09 V
E = -2.61 V
F = -5.22 V

Thanx for your reply.voltages as follows.
A 0.00
B 0.45
C 3.62
D 2.94
E no c30
F --1.09

E C26 --1.08
Sorry for the confusion

It seems there may be excessive load on the -5V supply.
Please remove IC1 and IC2 and measure again the voltage over ZD1.

Voltage over zd1 is now --4.5v

It seems the charge pump is too “weak” for some reason.
The output voltage should be -5.2V.

Please check the battery voltage.
Should be 6V when the power switch is turned to ON position?

Fitted new batteries. Read 6.05v when turned on.
Voltage over zd1 still --4.5v

OK, no problem with the battery.
Would you please check again the voltages A and C.
For EDU08 they should be about:
A 1.67 V
C 5.1 V


A reads 1.66
C reads 4.02
This is with ic’s 1 & 2 fitted

For some reason the voltage C is too low.
Please check voltages G and H.
They should be about:
G: 5.9 V
H: 6.0 V

G reads 5.80
H reads 5.86

The G and H voltages are OK.
The voltage on point C should be about 0.7V lower than on point G.
Due to the base to emitter threshold voltage of about 0.7V of T4, the voltage on point C should be about 5.1V.

The charge pump problem seems to be very tricky…
Also the original problem concerning the menu button press is not yet resolved.

You can return the kit for inspection/repair to your local Velleman dealer or direct to:

Velleman Projects Tech. Dept.
Legen Heirweg 33
9890 Gavere

What are your charges for this?

Here you’ll find info about the warranty on kits.