I have both the 576 and 577 and when I first started using the 577, I thought that it had died or had some other defect when I first noticed that "dimming dot" phenomenon. I wish the engineers on the 576 had been so perceptive and included this feature in that machine as well. Both machines are incredible in their own right. I converted my 577 D2 over to a D1 for the reason that you are explaining in your previous posts. I keep learning more every day while using these instruments. One thing that I found interesting is observing the trace of a tunnel diode. Seeing things visually makes all the difference in the world to me when it comes to understanding what is going on in a component. I appreciate your comments and learn something new from almost every one of them. I hope Peter can get his 576 in top condition.