Calibration failure EDU09

Calibration results:

Results are

CH1 offset at 2V/div : 77 FAIL
Rounds : 51
CH1 offset at 1V/div : -46 OK
Rounds : 51
CH1 Y-position low, CH1_DAC1 202 0
Rounds : 33
CH1 Y-position mid, CH1_DAC0 202 77
Rounds : 51
CH1 Y-position high, CH1_DAC2 201 255
Rounds : 32

Voltages on IC2 are incorrect. No -5v produced , so I assume no drive from oscillator to T1 and T2.

Supply voltages to IC3 apperar OK.

Please check the voltages A…F.
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

If voltage ‘A’ is about 1.6V, the drive from oscillator can be OK.



Thanks for the helpful diagrams : I will send the voltages soon Ragnar

My readings are:-

A 1.64
B 0.51
C 3.39
D 4.93
E 0.35 positive
F 0.69 positive

Does this help to locatise the fault ?

Thanks for your assistance Ragnar

The voltage C = 3.39V seems strange.
Please check the voltage on the base pin (middle pin) of T3.
There should be same voltage as C.

Check also the transistor types are correct:
T1: BC337
T3: BC327

Check all soldering joints of the transistors and components around them.

I’m sorry, the voltage on gave on C was a typo : it should have been 4.49. I have now remeasured all the leads of the two transistors ( they are in the correct positions ) they are :-

T3 e 4.98 b 4.43 c 4.98 I identify the collector as the left pin on the diagram you sent me.

T1 e 0.31 b 0.51 c 4.98 I identify the collector as the left pin on the diagram you sent me.

I have examined the soldering. I will try re-soldering the transistor connections.


Re-soldered the connections and tried to calibrate it. Success !!

Thanks for all the help . I will now have to see how to use it : it did get a small record from my finger on the live input.

No problem!
Glad to hear the issue is resolved.