Calibration fails: CH1 offset at 1V/div : 201 FAIL

Edukits EDU09
1

Hi,

I have assembled the EDU09 oscilloscoop, but the calibration failed. In the calibration log I found:

Calibration results:

CH1 offset at 5V/div : 161 OK
CH1 offset at 1V/div : 201 FAIL
CH1 Y-position low 32
CH1 Y-position mid 67
CH1 Y-position high 67

What did I check:
Check T1, T2 and T3
voltage over the zener diode ZD1: about 5V
E (voltage C30)= -2.6V
F (voltage C31)= -5.2V
Corrected the orientation of the 8 pin IC : was placed the wrong way around because of the missing notch.

In other post I read about no connection between C30 and C31. But how to check?

Please help me out.

regards, gGuzz

2

The charge pump seems to work OK.
The problem is IC2 (the 8 pin IC).
Please check the voltage on pin 1 of IC2, should be about 1.65V
On pin 7 there should be about -1.65V.
On pins 2, 3, 5 and 6 should be 0.0V.

3

Thank you for the quick reply.

I am not shure on how to measure these voltages, where should I reference the 0 V?
I measured between
pin 2-1: 2,67 V
pin 2-7: -1,55 V

pin 2-3: 0 V
pin 2-5: 0 V
pin 2-6: 0 V

pin 2-8: 5 V

4

You can reference the USB connector shield (soldered to the ground plane).

Anyhow it seems the voltage on pin 1 of IC2 is too high.

Please check the resistor values: R18, R19, R23, R25 and R27.

5

This tip pointed me into the right direction. R27 and R28 were swapped.
The kit is working.

Thanks for your support!

Calibration results:

CH1 offset at 5V/div : 132 OK
CH1 offset at 1V/div : 0 OK
CH1 Y-position low 32
CH1 Y-position mid 128
CH1 Y-position high 223

6

Hi,

I get the same trouble regarding the calibration.

Calibration results:

CH1 offset at 5V/div : 161 OK
CH1 offset at 1V/div : 201 FAIL
CH1 Y-position low 24
CH1 Y-position mid 24
CH1 Y-position high 24

I checked IC2 as that’s said above. And I measured pin 8 and 4. I found 10,30 V. But, I think the good must be around 5V. What about you ? Which voltage did you find regarding pin 8 and 4 ?

7

[quote=“chri$”]Hi,

I get the same trouble regarding the calibration.

Calibration results:

CH1 offset at 5V/div : 161 OK
CH1 offset at 1V/div : 201 FAIL
CH1 Y-position low 24
CH1 Y-position mid 24
CH1 Y-position high 24

I checked IC2 as that’s said above. And I measured pin 8 and 4. I found 10,30 V. But, I think the good must be around 5V. What about you ? Which voltage did you find regarding pin 8 and 4 ?[/quote]

Here’s my result during the checking:

pin 1: around 3,3 V
pin 7: 1,74 V (between 5 and 7)
-2,55 V (between 6 and 7)
between 2 and 3 = 4,32 V
between 5 and 6 = 0,24 V

8

It seems the voltage on pin 1 of IC2 is too high.
Have you checked the resistor values: R18, R19, R23, R25, R27, R9 and R10 ?

Here are the voltages on the pins of IC2 to GND (e.g. SK2).
The PC program is not running when measured.
IC2 pin 1: 1.64V
IC2 pin 2: 0.00V
IC2 pin 3: 0.00V
IC2 pin 4: -5.1V
IC2 pin 5: 0.00V
IC2 pin 6: 0.00V
IC2 pin 7: -1.63V
IC2 pin 8: 5.05 V

Please check and post the results.

9

Good afternoon,

Thanks for you reply. So I measured voltage of pins ic2 and resistor:

R18: 0,32 V
R19: 0,33 V
R23: 1,51 V
R25: 0,35 V
R27: 1,70 V
R9: 0,08 V
R10: 0,08 V

PINS:
1: -0,56 V
2: -0,05 V
3: 0 V
4: -5,21 V
5: -0,23 V
6: 1,6 V
7: -5,12 V
8: 5,09 V

10

There are some strange results.
You measured -5.12V on pin 7 and -0.05 on pin 2.
The resistor R23 is between the pins 7 and 2.
You measured 1,51V over R23. This is very strange result (should be about 5 V).

There ais also other strange result:
Pin 5 is directly connected to GND.
You measured -0,23V between the pin 5 and GND - this should not be possible!

Can you please measure once again all the voltages on all pins of IC2 to GND.

Have you checked IC2 is in right position?

11

I’ve put the red probe on the pins and the black on the GND.

12

[quote]I’ve put the red probe on the pins and the black on the GND.[/quote]This is OK.
A good GND is the shield of the USB connector or SK2 terminal of the input cable.

13

Regarding R23, I’ve found 4,55 V. Maybe, I confused myself before. But I’ve still found strange results about pins ic2.

14

Can you please list the voltages on all pins of IC2 to GND?

15

The most are the same:

1: -0,55 V
2: -0,05 V
3: 0 V
4: -5,22 V
5: -0,23 V
6: 1,54 V
7: 0,64 V
8: 5,11 V

Another trouble, it’s about R23. Now its voltage is 0,64 V.

16

The R23 voltage is now OK.
Anyhow, why there is still -0,23 V on pin 5.
This pin should be connected to GND, voltage should be 0,00 V !

17

Otherwise, I have a question regarding L1. The first time I’ve switched on the kit, it was burning a little. So, there are some burn. But, the kit work. (I think that problem overcame because i connected IC2 in the wrong side). So, its voltage is around 5V, right ? (What I found L1 = 5,11V Both sides of its pins and what i saw according to the pictoral diagram from page 17).

18

I got the problem. that’s R3, No voltage. Even if according the ohm test, the component is okay.

19

[quote]So, its voltage is around 5V, right ? (What I found L1 = 5,11V Both sides of its pins and what i saw according to the pictoral diagram from page 17).[/quote]Yes, the L1 seems to be OK.

[quote]I got the problem. that’s R3, No voltage. Even if according the ohm test, the component is okay.[/quote]Seems to be OK too. There should be no voltage over R3.