Broken PCB trace and problems with EDU 09


(I’m sorry, my english is not very good. I’ll try my best)

I’ve assembled the edu09 oscilloscope kit but I’m having some problems.

During the assembly I broke the PCB trace from ‘‘HI_GAIN’’ to R18 pin (looking at the electrical diagram). I soldered a wire from the R18 pin to the IC3 pin 7 hoping it would repair the connection.

When I connect the scope to the computer, the scope is recognized and the EDU09 program says that the calibration is successful. I have these results:

Calibration results:

CH1 offset at 2V/div : 131 OK
Rounds : 4
CH1 offset at 1V/div : -1 OK
Rounds : 7
CH1 Y-position low, CH1_DAC1 32 32
Rounds : 1
CH1 Y-position mid, CH1_DAC0 128 133
Rounds : 6
CH1 Y-position high, CH1_DAC2 224 225
Rounds : 2

I’ve looked up at some threads in the forum and I’ve done these measurements with a multimeter:

Volatge readings:

1 0
2 0
3 0
4 0
5 0
6 0
7 -5.13
8 0
9 4.96
10 0
11 0
12 0
13 0
14 0
15 0
16 0

1 4.89
2 0.37
3 0
4 -5.13
5 0
6 0
7 -1.65
8 4.96

Voltage readings according to the picture:


A 1.66
B 0.43
C 4.35
D 2.56
E -2.52
F -5.13

Now when I try to use the scope I have these results:

  • With the 5v, 2v and 1v divisions, if the probes are not connected, the trace on the scope window is at zero. If I connect a 9v battery the trace measures 3v, if I connect a 1.5v battery I get no readings.
  • With the 0.5v division, with the probes not connected, the trace ‘‘jumps out of’’ the window.
  • With the 0.2v, 0.1v divisions, if the probes are not connected the trace is not at zero, it measures some kind of singal with variable ripple and DC component, around 0.8v ±0.1v.

Can someone give me an advice ?

There on pin 9 of IC1 seems to be 4.96V.
This indicates that the microcontroller IC3 may have too high VDD supply voltage.
Please check the voltage on pin 20 of IC3.
The voltage should be 3.3V.
If not, please check the voltage regulator VR1 soldering and orientation and values of R5 and R14.

On pin 16 of IC1 there should be 5V. This voltage seems to be missing.
(Maybe bad connection or bad soldering or broken trace.)

I found a bad connection at the input stage, resoldered that one and some other bad looking points and luckily now the scope seems to be working. I tested it with 9v, 1.5v batteries and a square wave from an arduino and the measures are good.

Thanks for the help and the fast reply !

No problem. Glad to see you got it resolved.