On 2019-04-16 16:35, Alberto I2PHD wrote:

There is a suspect tantalum capacitor, which I did not replace, namely
C933, which is in the path that brings working voltage to the Delay Time Position control.... just as good measure, I
will replace that also...

Problem fixed. I replaced that suspect capacitor with a 4.7uF, 100V electrolytic, and now the delay time after which the B sweep starts is rock stable...

Now I have a suspect, which maybe somebody could confirm or deny... look at this photo of the replaced cap :

http://www.i2phd.org/public/tantalum2.2uF.jpg

Should the mark indicate the negative side of the cap, then it was soldered in reverse, with the marked side connected to +14V....
If instead it indicates the positive side, then no manufacturing errors....  I am not much familiar with the markings of the tantalum caps....

In any case, now my 475A is perfectly working, and this is what counts... :-)