[quote=“VEL417”]It is wrong to assume that we market ‘faulty’ kits. This particular kit has been available for over 10 years. Thousands have been sold. The circuit it a literal application of the data sheet.
We suggest that you return your kit for inspection/repair to:
Velleman Kit Tech. Dept.
Legen Heirweg 33
ALL LED’s ON PROBLEM HAS A SOLUTION VELLEMAN!
After pulling my hair out trying to figure out why the LED’s turn on full blast and stay on with the slightest turn of the potentiometer, I finally figured it out. The feedback resister and diode configuration, R2 and D1, changed the voltage drop at pin 2 of the 741 op amp (lower and lower voltage drop as you turn the pot clockwise) causing the output to go high, and thus turning on all the LED’s almost immediately. When I removed them (R2 and D1), the problem went away. The unit still detects voltage fine, and the good part is, no more ‘all LEDs are on and I can’t get them off’ nightmare! This problem has happened with at least three to four of my kits I’ve assembled out of about 20 we needed for work. I am an experienced engineer and still went nuts with this problem. It is NOT an assembly error. Not sure why some do this and some don’t, but maybe you you should just leave those components out from now on as to avoid disappointed customers.