Velleman K7105 - Calibrating the vertical amplifier


I am following the instructions, as described in the K7105 user manual, to calibrate the vertical amplifier but it appears to be impossible to “adjust the CALIBRATE potentiometer (RV3) until the RMS readout shows the same value as the multimeter.” The manual advises adjusting the Y-position until the waveform appears “completely within the display” to enable the mVr value to appear, but the waveform I am seeing is way too big to fit on-screen so the mVr reading never changes from “…mVr”. I am, therefore, unable to match the mVr value with that which is shown on my multimeter.

I have, as instructed, the time/div set to 1ms/div and the volt/div set to 50mV/div

Can anyone assist with this issue?

Most likely, the problem is due to an assembly problem.
This is a rather complex circuit and the unit has been obsolete for a quite a while now, so I’m afraid we are unable to solve this problem through this forum.
However, we can still service the unit. Should you wish to have it inspected, please return it to:

Velleman Projects Tech Dept.
Legen Heirweg 33
9890 Gavere

US residents: Please call (817) 284 77 85