I know nothing about those units, but is it possible that it is normal operation. Stop may mean stoping the rotation which takes time. Lifting the needle first may be required first..
Just a thought..

That may be normal operation, unless there is supposed to be some form of speed-activated electronic mute on the audio signal output. It would take huge pulses of energy to stop and start a professional turntable in 100ms or so.

I have a Thorens TD124 turntable, and that has a mechanical clutch that lifts a light rotating shell off the main flywheel, with the LP record sitting on the shell. The shell starts and stops in less than 1/10 of a revolution, but the flywheel keeps on turnin', as the old country song (nearly) has it.

Thanks, Boswell, Obviously the whole point of the EMT was the precision, such as the one concerning stop/start. But I wonder if there are some EMT owners who could come to help here ?

The main cueing feature seems to be the forward/reverse motion available by alternating pushes on the two buttons.

PS I have just found the spec on the 948: it gives a start time of 0.5 sec.

So it seems that the problem is related to the phono stage and Speed control unit because the EMT were conceived in such a
way that the sound only comes through after the sync light is green and the right speed is attained. Same for the stop button –
it should cut off the sound instantly.

Question of a technical simpleton: is this an electronic board - problem which is fine as the boards can be easily revised OR is it a hardware problem ?

Yes, that's what I was saying a couple of posts ago: the audio is muted until the turntable is up to speed. That would need one of the pairs of wires in the multiway connector.

Does the sync light come on only when the turntable is up to speed, or is a just a cue light from the control desk?

From memory it was about half a revolution, something like that - absolutely not an instant stop. What would be the point of an on-air stop. They still used green slip mats here - although I never saw very many back then. Nice engineering though.

The mute circuit was really just because speed ramping up sounds terrible on air. Many broadcast turntables of that era had bits of tape with marks showing the DJ or grams op how far to back cue the record, and of course to do that you had to be able to defeat the mute. Many presenters who used real scripts had to time the words to mark the script with the right cue point. Today’s instant start was so useful. Back timing was an essential skill back then. Happy days.

EDIT Got lost with the threads being merged - The thing with broadcast kit from the 60's-80's was not predominantly anything at all to do with audio quality, but reliability and ease of maintenance. Very often the people at home with top end hi-fi turntables had better speed regulation, an almost absence of noise, amazingly light tracking down pressure and very sensitive and fragile cartridges and stylus assemblies - things that the average DJ, presenter or grams op would break in their first use. We're talking about engineering - solid, heavy, able to withstand somebody drumming along with the music on the same surface the turntable is recessed into. We are NOT talking about sonic perfection - far from it, we're talking about workhorse products that can run 24 hours a day for weeks with little maintenance. Turntable arms designed to prevent the stylus jumping out of the groove when somebody sneezes. Your lack of mute may simply be the original owners bypassed it. Every organisation had their own preferences for many of these things. What annoyed the chief engineer most being the usual rule. If yours has the links fitted, it may just be a case of removing them to restore the mute function. Have you checked?