PCS100/K8031 - Calibration problem

Hi there,

I’ve built this oscilloscope, but when I try to calibrate it following the instructions (section 23. Test and adjustment), it doesn’t play ball.

Offset adjustment works okay, and I manage to tweak RV1 until the signal remains stable on the screen.

However, when I try to do the “transient adjustment and calibration” step, I select 1v/div, but the signal doesn’t fit into the scale on my screen so I can’t adjust CV1 because I can’t see the signal top.

If I skip this step and try to adjust RV2 to change the RMS value, I see that changing RV2 has no effect on the RMS value.

Any ideas?

Cheers,

Tony

It seems that the input attenuator is not working properly. Either there is faulty relay (RY2 closed all the time?) or some of the relay control signals ATT0 … ATT3 is not changing its state as it should. Please check the signals ATT0 … ATT3 from the relay pins. All of those should change state when you go through all the V/div ranges.
Check the relay soldering.

Thanks VEL255 I’ll try that. I also discovered that RV2 is dead (i.e. short-circuit) so that obviously needs to be fixed as well. Need to buy a 500ohm variable resistor now!