[Scott Dorsey]

wrote:
I have a revox a77, when on playing mode, the speed runs too fast, also when switching between 7 1/2 to 3 3/4, the casptain motor speed doesnt change.21 volt in 3 3/4 at pin ae 1 but speed not reduced

It's likely running open loop with no servo control at all. Check for shorted
transistors in the servo circuit, also check for bad decoupling capacitors
if the machine hasn't been recapped in the past decade.

The manual has a good discussion on locating servo problems. The scope will
tell you what is going on. In a pinch, Jon Hall in Charlottesville, VA might
still be willing to work on them if you catch him on a good day.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."