I got ADC200-50 from my friend how bought it 10 years ago and never used. I got parallel cable and power supply from local computer store, download and install software PicoFull_r5_20_8 and start the program. The led on ADC start blinking so communication was there. The problem is that it always shows just a straight line 20V and warning sign that input value exceed limit. I dind't connect even probe. I tryed different option but always the same. Can you please advise what can be the problem.