K8031 fails calibration.
3V,0.3V and 30mV V/DIV ranges all work correctly but 1V, 0.1V and 10mV V/DIV range have no trace, biased of scale?
Any suggestions.
Thanks.
Is this K8031 a new, just assembled or an old one?
Has it previously worked OK?
If new one, then check that the C26 is not in short circuit (a solder bridge somewhere in the circuit).
The K8031 is a few years old, and has previously worked without problem.
However the unit has not been used for some time and on attempting to re-use the unit, this fault was apparent.
On first detecting the fault I re-calibrated the unit repeating the “Test and Adjustment” procedure. The offset adjustment
was well out of adjustment in a downward direction, but could be reset to the screen center using RV1. Impossible to
balance 1V/div and 3V/div correctly, although both adjust with RV1.
The oscilloscope is now using the faulty calibration values from the file WinDso.ini.
This makes it impossible to adjust RV1 properly.
Please delete the file WinDso.ini from the folder: C:\Program Files\Velleman\PcLab2000SE
In Windows Vista the file should be deleted in this folder too:
C:\Users<username>\AppData\Local\VirtualStore\Program Files\Velleman\PcLab2000SE
After deleting the file make the offset adjustment:
• Make sure that the Y position slider is in the centre position
• Switch always between 1V/div and 3V/div setting
• Adjust RV1 until the signal remains stable in the centre of the screen
Removed WinDso.ini.
No trace on screen for 1V and 3V settings. Adjusting RV1 brings trace back on screen. Best balance between 1V and 3V settings leaves
an offset of just over one division at screen center, this - cannot be reduced.
There may be many causes to this problem.
Maybe electrolytic C23 is leaking…
What is the output voltage from trimpot RV1 compared to ground?
(I.e. measure the voltage between the BNC connector J1 shield and ground.)
Voltage between BNC connector and GND is 2.515V, rock steady with a range change between 1V and 3V/Div.
This looks OK.
Please do not try to adjust the trace to stay on the middle line of the screen.
Just adjust RV1 until trace remains stable.
I.e. no trace jump on the screen when you change between 1V/div and 3V/div.
Finally use the calibrate and exit option in the File menu to complete the calibration.
It seems the document should be:
Offset adjustment:
• Make sure that the Y position slider is in the centre position
• Switch always between 1V/div and 3V/div setting
• Adjust RV1 until the signal [color=#800000]remains stable[/color] [color=#000080]about[/color] in the centre of the screen
Success! By experiment the position to obtain balance between 1 and 3V/Div is a position approx. one division up from the center line. (2.534V).
The calibration now completes OK and the oscilloscope works correctly on all ranges.
Thanks for your assistance, much appreciated.