[Radioroslyn]

What does your A voltage volt look like? Are you 6v or better? Why did you replace the chopper?? Old one missing or bad?? You may what to check the B current to see that it is like, would expect maybe 45-50 ma with a single end output stage or 70-80ma with P/P. If you have the old chopper I'd cut it open  and clean/file the contacts to see if the S/S one is doing something goofy.

Terry
ps Welcome back Bob!